Republic of Latvia Cabinet Regulation No. 329 Adopted 30 June 2015

Regulations Regarding the Latvian Building Code LBN 224-15, Land Amelioration Systems and Hydrotechnical Structures

Issued pursuant to
Section 5, Paragraph one, Clause 3
of the Construction Law

1. The Regulation approves the Latvian Building Code LBN 224-15, Land Amelioration Systems and Hydrotechnical Structures (hereinafter - the Latvian Building Code LBN 224-15).

2. The Ministry of Economics shall, in cooperation with the relevant technical committee for standardisation, recommend to the national standardisation body a list of standards that need to be developed, adapted, and applied in connection with this Regulation.

3. The national standardisation body shall publish a list of Latvian national standards to be applied for the purpose of enforcement of the Latvian Building Code LBN 224-15 on the website www.lvs.lv.

4. The building designs which have been drawn up or submitted for agreement thereupon to the building authority in accordance with specific procedures prior to the date of coming into force of this Regulation in accordance with the requirements of the laws and regulations applied at the relevant time need not be revised in accordance with the Latvian Building Code LBN 224-15.

Prime Minister Laimdota Straujuma

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Approved by
Cabinet Regulation No. 329
of 30 June 2015

Latvian Building Code LBN 224-15, Land Amelioration Systems and Hydrotechnical Structures

1. General Provisions

1. The Building Code prescribes the requirements for the design of land amelioration systems and hydrotechnical structures and for the hydrological calculations of surface water bodies.

2. Terms used in the Building Code:

2.1. protecting dike - a ground hydrotechnical structure for the protection of a territory against flooding;

2.2. dam - a hydrotechnical structure for retaining runoff and regulating water level;

2.3. discharge gate - a device of a hydrotechnical structure used to close an opening;

2.4. inverted filter - a device of a hydrotechnical structure for preventing filtration deformations in soil, consisting of two or more layers of water-permeable soil of varying coarseness, arranged in increasing order of soil particle size in the direction of the filtration flow;

2.5. estimated hydrological parameters - hydrological parameters (flow rates, water levels) calculated with a specified exceedance probability which serve as the basis for determining the most important dimensions of land amelioration systems and hydrotechnical structures and for water resource planning;

2.6. irrigation - artificial supply and distribution of water to replenish soil moisture reserves during the plant vegetation period;

2.7. irrigation norm - the amount of water or the thickness of the water layer to be supplied by irrigation to maintain the optimal soil moisture regime for the crop to be irrigated throughout the vegetation period;

2.8. irrigation system - a set of amelioration structures (specialised structures) and devices for land irrigation;

2.9. reach - a section of a surface water body adjoining a water retaining structure (dam) and located on each side of it, the upper side being the upper reach and the lower side being the lower reach;

2.10. flow rate - the amount of water that flows through the active cross-sectional area of a watercourse or structure per unit of time;

2.11. throughput capacity - the flow rate that can be discharged by the watercourse bed or a hydrotechnical structure at the required water flow depth and under other conditions;

2.12. dam - a hydrotechnical structure for the distribution, regulation of water flow or impoundment;

2.13. stream bed gradient - the ratio of the difference in bottom elevations of a section of a watercourse bed to the length of that section;

2.14. two-way land amelioration system - a drainage system which may also be used for land irrigation;

2.15. drain - a sub-surface structure of a land amelioration system or hydrotechnical structure for collecting and conveying soil and filtration water, constructed as a pipe or hollow body made of soil, local or industrially manufactured materials;

2.16. drain well - a structure of the drain system for the precipitation of the silt entering the drainage, for connecting collectors, for sharp changes in the longitudinal gradient and route alignment of collectors, for introducing surface runoff or water inflow into the drain system, and for visual inspection of drainage operation;

2.17. filter - a structure of the drain system to increase the efficiency of drainage operation in terrain depressions and in low-permeability, trampled soils which protects the drain pipeline from the entry of suspended solid soil particles into the drain;

2.18. drain collector - a drain pipeline that collects the soil or filtration water received by the drainage pipes and conveys it into an open bed;

2.19. drain system (drainage) - a set of hydraulically connected and subordinate drains which collects and conveys soil or filtration water to an open bed through a single source;

2.20. ecological flow - the portion of water inflow which, under any operating conditions of the dam hydrotechnical node, must be conveyed into the lower reach of the hydrotechnical node;

2.21. fascine - a cylindrical bundle tied from branches or twigs, used for strengthening the beds, embankments, or excavation slopes of land amelioration systems or hydrotechnical structures;

2.22. ditch - a structure of the land amelioration system which collects surface and groundwater runoff from the area to be ameliorated and lowers the groundwater level (surface drainage trench), encloses the area to be ameliorated from the surface water and groundwater of the surrounding area (contour ditch, interceptor ditch);

2.23. bed - a natural or artificially created depression in the land surface in which water flows or accumulates;

2.24. bed roughness - the totality of bed irregularities which creates resistance to water flow and cause its pressure losses;

2.25. hydraulic radius - a parameter characterising the water flow, namely, the ratio of the active cross-sectional area of the bed to a parameter characterising the water flow which is the length of the contact line between the water and the bed from the water line on one bank to the water line on the other bank (the wet perimeter);

2.26. hydrotechnical structures - structures subject to water pressure and serving for the use of water resources or for the prevention of the harmful effects of waters;

2.27. engineering protection - protection of the coastal area of a water body against flooding or overwetting;

2.28. outlet - a structure of the drain system for discharging the drain collector into an open bed;

2.29. port and marine hydrotechnical structures - hydrotechnical and navigation structures at sea, in ports, shipbuilding enterprises, and in navigable watercourses and water bodies where special requirements for navigation are established;

2.30. canal - an artificial surface water body that collects and conveys runoff from land amelioration systems, other territories, or surface water bodies.

2.31. peat field ditch - a surface drainage trench of the peat deposit drainage system;

2.32. colmatage - the filling of soil or filter pores or the deposition of fine soil particles and chemical compounds on the surface of soil or filter pores during the water filtration process, reducing the permeability of the soil and filter, as well as the artificial elevation of the land surface with imported or dredged soil;

2.33. large-diameter collector - a drainage system pipeline through which drainage runoff from the drain system and surface waters is conveyed, with a diameter equal to or greater than 300 mm;

2.34. land amelioration system - a set of amelioration structures (specialised structures) and devices for regulating the land water regime;

2.35. slope gradient coefficient - the ratio between the horizontal and vertical projections of the embankment or entrenchment slope;

2.36. drainage system - a set of amelioration structures (specialised structures) for land drainage;

2.37. runoff - the terrestrial stage of the natural water cycle which occurs over the land surface (surface runoff), through the soil and rock layers (subsurface runoff);

2.38. runoff layer - the volume of runoff from a unit of catchment area, expressed in millimetres of water layer;

2.39. diverting ditch - a drainage system structure that receives water inflow from the regulatory and boundary grid of the drainage system of a single property and conveys it to a water drain, water body, or the sea;

2.40. spring flood - the phase of the hydrological regime of a surface water body, characterised in spring by a high water level resulting from snow and ice melt;

2.41. alluvial area - the part of a watercourse valley which is periodically flooded during spring or other flood;

2.42. hydrological verification parameters - hydrological parameters (flow rate, water levels) calculated with a specified exceedance probability for verifying the main dimensions of water retaining and drainage structures and for the operation of the structure under extreme conditions;

2.43. spillway - a water drainage structure over which water flows across a crest, forming a free-flowing surface;

2.44. exceedance probability - the number of cases, expressed as a percentage of the total number of cases, in which an estimated hydrological parameter or hydrological verification parameter is exceeded;

2.45. polder - a drained area that is separated from rising waters, but runoff is conveyed from the protected area by pumping;

2.46. polder basin - an area from which surface and groundwater runoff is conveyed from the polder area, as well as from the adjacent area;

2.47. polder area - an area which, prior to the construction of protecting dikes, was flooded during an estimated spring or other flood and is protected from overwetting and whose runoff is pumped by a pumping station;

2.48. confluence - a drain system structure for connecting drain collectors;

2.49. covered well- a drain well located below the land surface level;

2.50. stop plank - a beam inserted horizontally in the opening of a hydrotechnical structure to block the opening and to regulate the water level;

2.51. gully - a drain well for introducing surface runoff and inflow from a contour ditch or road ditch into the drainage system, as well as for visual inspection of drainage operation;

2.52. water drain - a natural or regulated watercourse (a river, stream), as well as a specially excavated bed collecting and conveying runoff from several land amelioration systems, other areas or surface water bodies. Derivation channels excavated for hydropower purposes are not considered water drains;

2.53. water intake structure - a facility for taking water from a surface or groundwater water body;

2.54. water resources - the volume of water potentially available for use at a specific time and location (area);

2.55. surface runoff drainage chute - a drainage system structure (a furrow, pipe, fascine) for conveying surface waters from the area to be drained into a ditch, diverting ditch, or water drain;

2.56. surface water collector - a drain system structure for collecting surface runoff and introducing it into the drainage system.

3. The Building Code does not apply to:

3.1. port and marine hydrotechnical structures;

3.2. water drainage structures with a throughput capacity greater than 1000 m³/s;

3.3. Class A hydrotechnical structures of hydroelectric power plants.

4. Land amelioration systems and hydrotechnical structures shall be designed in accordance with this Building Code and other legal acts in the fields of construction, land amelioration, and environmental protection.

5. In the design of land amelioration systems and hydrotechnical structures, the standards published by the national standardisation body on the website www.lvs.lv shall be applied.

2. Hydrological Calculations

6. The possibilities for constructing land amelioration systems, as well as the parameters and stability of engineering protection, hydrotechnical, and transport structures in populated areas shall be determined depending on the hydrological regime of surface water bodies.

7. In the hydrological calculations of land amelioration systems, engineering protection, hydrotechnical, and transport structures and surface water bodies, estimated flow rates Q (m³/s), water levels H (m), stream velocities v (m/s), and runoff modules (l/s × ha) with annual exceedance probability in percent (Annex 1 to this Building Code) shall be used.

8. The estimated hydrological parameters shall be determined as follows:

8.1. by mathematical statistical methods based on direct hydrometric observations if hydrometric observations have been carried out in the designed catchment area and data are available with at least 25 years of continuous observation series. For determining the statistical parameters of the series, the method of moments (with appropriate justification, other methods may be used, for example, empirical assurance curves for processing water level data) and the Pearson III probability distribution, while for maximum flow rates - the Gumbel probability distribution shall be used;

8.2. by empirical formulas and isoline maps compiled by summarising the hydrometric observations carried out, if no observations have been made in the catchment area to be designed;

8.3. using statistical methods for the extension of the observation series if the continuous observation series in the catchment area is shorter than 25 years. The statistical extension of observation series may be used if the correlation coefficient between flow rates during the coinciding runoff formation phases for the series to be extended and the reference station is no less than 0.75.

9. The maximum spring tide flow rate with a 1 % exceedance probability Q1 % (m³/s) shall be calculated, using the following formula:

Q_{1 %} = K_{1 %} × δ × δ₁ × δ₂ (A + 1)^{- 0.14} × A, where (1):

K_{1 %} - the parameter characterising the swiftness of the spring tide with a 1 % exceedance probability; its values are specified in Map 1 of Annex 2 to this Building Code;

δ - the coefficient accounting for the regulatory effect of water bodies;

δ₁ - the coefficient accounting for the maximum flow rate depending on the forest area in the catchment area;

δ₂ - the coefficient accounting for the maximum flow rate depending on the bog area in the catchment area;

A - catchment area (km²);

9.1. the coefficient δ shall be calculated by multiplying the individual impact coefficients of all water bodies in the catchment area:

δ = r₁ × r₂ ... r_i ... r_n-1... r_n, where (2):

r_i - the impact coefficient of the i-th water body (lake) which is applied to the calculation section;

9.2. the impact coefficients of each water body on the maximum flow rate in the calculation section shall be determined, using the following formula:

ri = 1 -	14.2 × Si0.355 × Ai0.73	, where (3):
	H11 %0.5 × A

A_i - the catchment area for the i-th water body (km²);

A - the catchment area in the calculation section (km²);

S_i - the surface area of the i-th water body (km²);

H1_{1 %} - the spring tide runoff layer (mm) with a 1 % exceedance probability the values of which are specified in the Map 2 of Annex 2 to this Building Code;

9.3. the forest impact coefficient δ ₁ is calculated, using the following formula:

δ₁ = (A_m + 1) ^{- 0.22}, where (4):

A_m - the relative forest area in the basin (%). If the relative forest area is less than 5 %, then a value of A_m = 5 % is assumed;

9.4. the bog impact coefficient δ ₂ is calculated, using the following formula:

δ₂ = 1 - 0.7 × lg (0.1 A_p + 1), where (5):

A_p - the relative bog area in the basin (%);

9.5. the flow rate with a different exceedance probability is obtained by applying the following transition coefficients:

9.5.1. Q_{2 %} = 0.88 × Q_{1 %};

9.5.2. Q_{3 %} = 0.82 × Q_{1 %};

9.5.3. Q_{5 %} = 0.74 × Q_{1 %};

9.5.4. Q_{10 %} = 0.63 × Q_{1 %}.

10. The maximum flow rate of summer or autumn floods Q_{p %} (m³/s) shall be determined, using the following formula:

Qp % = q200 ×(	200	)0.22 δ × δ2 × λp % × A, where (6):
	A+1

q₂₀₀ - the summer-autumn flood maximum runoff module (m³/s × km²) with a 1 % annual exceedance probability for a catchment area of 200 km² at δ = δ ₂ = 1, as determined in the Map of Annex 3 to this Building Code;

λ _{p %} - the coefficient for transition from the maximum flow rate with a 1 % exceedance probability to other probability values:

λ _{1 %} = 1.00; λ _{2 %} = 0.85; λ _{3 %} = 0.77; λ _{5 %} = 0.67; λ _{10 %} = 0.55;

A - catchment area (km²);

δ - the coefficient accounting for the regulatory effect of water bodies;

δ₂ - the coefficient accounting for the regulatory effect of bogs;

10.1. the coefficient δ shall be calculated, using the following formulas:

δ = (1 + 0.4 × A_ez)^-1, where (7):

A_ez - the reduced water body area (%);

Aez = ∑	(100 × Si ×Ai)	, where (8):
	A2

n - the number of water bodies,

i - the sequence number of the water body,

S_i - surface area of the water body (km²),

A_i - catchment area of the water body (km²);

10.2. the coefficient δ ₂ shall be calculated, using the following formula:

δ ₂ = 1 - 0.5 × lg (0.1 × A_p + 1), where (9):

A_p - the relative bog area in the basin (%).

11. The long-term annual average runoff layer (mm) shall be determined, using the Map of Annex 4 to this Building Code. By dividing this runoff layer value by 31.56, the long-term average runoff modulus q (l/s × km²) shall be obtained.

12. The summer half-year average runoff modulus q_v (l/s × km²) shall be determined, using the Map in Annex 5 to this Building Code.

13. The minimum 30-day flow rates Q for summer and winter low-water periods_{min. 30 d.} (l/s) shall be calculated, using the following formula:

Q_{min. 30 d.} = a × (A - c)^1.22, where (10):

A - catchment area (km²);

a and c - parameters depending on the geographical location of the basin, as well as the geomorphological and hydrogeological conditions:

13.1. depending on the geomorphological and soil conditions, four zones shall be distinguished in the territory of Latvia (Map 1 in Annex 6 to this Building Code):

13.1.1. clay plains (R₁);

13.1.2. moraine and sandy plains (R₂);

13.1.3. moraine uplands (R₃);

13.1.4. marginal zones (R₄);

13.2. if the catchment area is located in several zones, the proportional distribution among the respective zones shall be determined; in the general case: R₁ + R₂ + R₃ +R₄ = 100. After the distribution of the catchment area by zones, the parameters a and c shall be calculated, using the following formulas:

a = g × (a₁ × R₁ + a₂ × R₂ + a₃ × R₃ + a₄ × R₄), (11)

c = b × (a₁ × R₁ + a₂ × R₂ + a₃ × R₃ + a₄ × R₄)^-1, where (12):

g - the parameter of climatic conditions for the formation of minimum runoff which is determined, using the Map 2 and Map 3 of Annex 6 to this Building Code;

a₁, a₂, a₃, a₄, b - parameters as given in Table 1 of Annex 6 to this Building Code.

3. Agricultural Land Amelioration Systems

3.1. General Requirements

14. Agricultural land amelioration systems shall ensure the optimal water-air regime in the soil required for crop cultivation and field management.

15. For overwetted soils, drainage (drain or ditch) systems shall be designed. If the soil moisture under natural conditions does not meet the water requirements of crops, irrigation or dual-action land amelioration systems shall be designed.

16. The drainage of agricultural land by using systematic drainage is the most effective and radical method for land improvement and long-term increase of soil fertility. In light (sand or multilayer) soils, the design of a surface drainage trench network shall also be acceptable, but drainage shall be designed for land intended for intensive use and in clay soils.

17. Areas with complex hydrogeological conditions shall be drained, using several methods, or it shall be recommended not to use them as agricultural land. If the drainage of areas for agricultural use is designed in several stages, then in the first stage of drainage a diverting ditch, barrier ditches, and main surface drainage trenches shall be excavated only in distinctly overwetted places. In the second stage, the remaining drainage ditch network or drainage shall be installed.

18. Simultaneously with the construction of land amelioration systems, the regulation of surface runoff, deep loosening of the soil, and the necessary agrotechnical measures shall be designed.

3.2. Water Drains and Diverting Ditches

19. For the collection and removal of runoff from the area to be drained, water drains and diverting ditches shall be designed. A water drain is usually a direct continuation of the diverting ditch outside the area to be drained.

20. The diverting ditch shall begin at the outflow of the drain system, the confluence of two surface drainage trenches, contour ditches, or road ditches.

21. The water drain and the diverting ditch shall ensure:

21.1. the discharge of the estimated flow rate - the maximum spring tide flow rate with a 10 % exceedance probability - through the selected cross-section, without flooding the surrounding fields, or, depending on the grass species, allowing temporary flooding of grasslands for no longer than 10 to 30 days;

21.2. the discharge of the estimated flow rate - the maximum summer-autumn flood flow rate with a 2 % exceedance probability - through the selected cross-section, without flooding the surrounding fields and pastures;

21.3. the discharge of the verification flow rate - the maximum summer-autumn flood flow rate with a 10 % exceedance probability - through the selected cross-section, without flooding the surrounding meadows or forests;

21.4. that the average water levels in the water drain or diverting ditch during the summer half-year guarantee the collection and conveyance of the estimated flow rate of the drainage network (drainage, surface drainage trenches, contour ditches, road ditches) without water impounding level.

22. If the watercourse in its natural state is unable to meet the requirements laid down in Paragraph 21 of this Building Code, its regulation shall be designed by increasing the bed cross-section or longitudinal slope, reducing the bed roughness, or protecting the surrounding areas from flooding with a protecting dike and runoff pumping by constructing a polder.

23. The throughput capacity of the bed of a water drain or diverting ditch shall be determined by a hydraulic calculation of the bed, and the adequacy of the selected bed parameters for the conveyance of the estimated flow rate shall be verified in accordance with the requirements of Paragraph 21 of this Building Code. The cross-section of the designed bed shall be stable, and the estimated flow rate therein shall not develop a greater tractive force or stream velocity than is permissible for the relevant soil or reinforcements of the bed:

23.1. in the case of a steady water flow, the following formula shall be used:

Q_ap. ≤ Q = ω × v_vid, where (13):

Q_ap. - the estimated flow rate (m³/s);

Q - the bed throughput capacity (m³/s);

ω - the active cross-sectional area of the water flow (m²);

v_vid - the average stream velocity (m/s);

v_vid = C √R × i, where (14):

C - the speed (Chézy) coefficient (m^0.5/s);

R - the hydraulic radius of the active cross-sectional area (m);

i - longitudinal gradient of the bed bottom;

23.2. the numerical values of the Chézy coefficient C, depending on the bed roughness coefficient, shall be determined, using formula No. 15 or special auxiliary calculation tables.

C = 1 / n × R^1/6, where (15):

n - the roughness coefficient the values of which for the design of water drains and diverting ditches shall be assumed as follows:

n = 0.035-0.040 - if the estimated flow rate of the water drain is less than 3 m³/s;

n = 0.030-0.0325 - if the estimated flow rate of the water drain is from 3 up to 25 m³/s;

n = 0.025-0.0275 - if the estimated flow rate of the water drain is greater than 25 m³/s;

n = 0.040 - for a diverting ditch.

The lower n values shall be used if the soil is without stones or gravel, and the higher values - if the soil contains them.

24. Water drains, diverting ditches or their sections may become silted over time, become overgrown with aquatic plants or shrubs, or otherwise lose their water intake and drainage capacities. In order to restore the bed parameters and to ensure the required water levels, reconstruction or restoration works of the water drain or diverting ditch shall be designed.

25. The routes of diverting ditches shall be designed in conjunction with the design of detailed drainage, irrigation, and road networks, with forming the fields of rational shape and size, as well as taking into account the specific engineering geological and hydrogeological conditions in the area to be ameliorated.

26. Two straight sections of the diverting ditch route shall be connected by a curve the radius of curvature r (m) of which shall be assumed as r = 5 × B, where B is the width of the bed at the water level (m) at the estimated flow rate.

27. Two straight sections of the water drain route shall be connected by a curve the minimum radius of curvature of which is calculated, using the following formula:

rmin =	v2 × R4/3	, where (16):
	(v02 - v2/2) × cos φ

v - stream velocity (m/s) at the estimated flow rate;

v₀ - permissible stream velocity (m/s), as determined using Tables 1 and 2 of Annex 7 to this Building Code;

R - hydraulic radius (m);

cos φ - cosine function of the slope angle of the outer (concave) slope of the bed. For trapezoidal beds with a slope gradient coefficient m = 1.5, cos φ = 0.832, but with m = 2, cos φ = 0.894. For beds with parabolic, circular segment and combined cross-sections, cos φ = 1.

28. The permissible stream velocities v₀ (m/s) in unprotected and protected beds, depending on the soil characteristics and water depth in the bed at the estimated flow rate, shall be determined, using Tables 1 and 2 of Annex 7 to this Building Code.

29. In cases where it is necessary to reinforce the straight sections of the bed, if v > v₀, the radius of the curve shall be calculated depending on the permissible stream velocity v corresponding to the selected type of reinforcement₀ (Table 2 of Annex 7 to this Building Code). For reconstructed water drains with the design flow rate greater than 5 m³/s, the radius of curvature shall be within the range from 5 × B to 20 × B, adapting to the existing bed route in situ, where B is the bed width at the water level (m) at the estimated flow rate.

30. For the selection of the type of bed reinforcement for the concave (outer) slope of a curve, the effective stream velocity on the outer slope v₁ (m/s) shall be calculated, using the following formula:

v1 = v √

0.71 + 55 × R4/3/r1

, where (17):

v - stream velocity in the straight section at the same active cross-sectional area (m/s);

r₁ - the freely selected or existing radius of curvature of the bed (m). If the calculated v₁ is greater than the permissible velocity in the straight section v₀ (Table 1 of Annex 7 to this Building Code), then the outer (concave) slope of the curve shall be reinforced. If the radius of curvature calculated, using the formula No. 16, exceeds 20 × B or is negative, then a suitable bed reinforcement shall be selected for which the radius of curvature is within the specified limits, but no less than 5 × B.

31. The depth and cross-section of water drains and diverting ditch beds shall be such as to meet the requirements of Paragraph 21 of this Building Code, and the bottom elevations of the incoming drain outlets shall be at least 0.5 m above the bed bottom and 0.2 m above the average water level of the summer half-year. At the upstream ends of diverting ditches, the elevations of drain outlets may be designed 0.3 m above the bed bottom.

32. If the drains discharge into a water body, then the marks of the drain outlets shall be at least 0.2 m above the normal water impounding level in the water reservoir and the average water level in the lake or pond.

33. When connecting two small basin diverting ditches with a catchment area of less than 0.5 km², the bed bottom marks shall be designed at the same mark level. If the diverting ditch to be connected is shallower, then in its lower part the bed bottom gradient shall be increased or reinforced.

34. A small basin diverting ditch shall be connected to a bed with a permanent water flow so that the bottom of the diverting ditch is at the same mark as the average water level of the summer half-year in the receiving bed.

35. When connecting beds with a permanent water flow, they shall be connected so that the water levels at the estimated flow rates are at the same mark.

36. The parameters of the cross-sections (depth, bottom width) of water drains and diverting ditches shall be determined by hydraulic calculation, and the slope coefficients shall be accepted depending on the soil conditions:

36.1. m = 1.5 in clay and heavy loam soil;

36.2. m = 3.0 in silty sand soil;

36.3. m = 2.0 in other soils;

36.4. m = 1.5 in forests, regardless of soil conditions.

37. The cross-section of diverting ditches shall be designed as trapezoidal with a minimum bottom width of 0.4 m and a slope coefficient in accordance with Paragraph 36 of this Building Code.

38. If the catchment area of the water drain is from 50 up to 100 km² or if the hydraulic calculation determines that the bottom width of the trapezoidal cross-section of the water drain is greater than 2.0 m, a parabolic or circular segment cross-section shall be designed.

39. In places where there is a large difference in stability between the upper and lower soil layers or also a large difference between the spring flood and summer half-year average flow rates, a composite double trapezoidal cross-section shall be designed.

40. The stability of bed slopes in light (sand, loamy sand) soils shall be verified by calculating the slope stability coefficient η, using the following formula:

η =	(γ - 1) × (1 - P) × cos α × tg φ	, where (18):
	P × tg α + (γ - 1) × (1 - P) × sin α

γ - specific density of soil (t/m³);

P - soil porosity (%);

α - bed slope gradient angle;

φ - internal friction angle of water-saturated ground. If the coefficient η is greater than 1, then the ditch slope is stable; if the coefficient η is less than 1, then the slope is unstable and reinforcements shall be designed.

41. Deformations of slopes caused by groundwater flow shall be prevented by installing bed reinforcements or bank drainage to intercept the groundwater flow. Bank drains with a pipe diameter of 75 mm or greater shall be installed no further than 1/4 of the drain spacing and no closer than 4 m from the bed baulk.

42. If bed instability is caused by stream velocities due to an increased bottom longitudinal gradient of the water drain or diverting ditch, the bed shall be reinforced along its entire length, or the longitudinal gradient shall be concentrated in short, specially reinforced bed sections by designing a rapid or drop structure.

43. The bed slopes shall be reinforced 0.1 to 0.2 m above the water level in the case of the estimated flow rate.

44. At locations of concentrated surface water inflow, surface runoff discharge chutes shall be installed.

45. The minimum longitudinal gradient of the diverting ditch bottom shall be 0.5 ‰. The minimum longitudinal gradient of the water drain bottom shall ensure the mean stream velocity of at least 0.1 m/s for the average flow rate during the summer half-year.

46. The depth of the water drain and diverting ditch in peatland, if the peat layer is deeper than the designed bed bottom mark, shall be designed, taking into account the settlement of the peat surface and the bed bottom (base). The bed longitudinal gradient shall be designed so that, after peat settlement, the bed attains a uniform bottom longitudinal gradient.

47. For transport and movement between different areas to be drained, as well as for the management of land amelioration systems, culverts, bridges, footbridges, and plank-ways shall be designed.

48. The throughput capacity of culverts in land amelioration systems and surface water bodies shall be determined by hydraulic calculation or using hydraulic parameter nomograms prepared by the pipe manufacturer, with the estimated flow rate filling up to 3/4 of the pipe diameter or up to 5/6 of the height of a rectangular pipe (in a non-pressure regime). If a partial pressure regime (the water depth before the culvert exceeds the culvert diameter or height by 20 to 40 %) or pressure regime (the water depth before the culvert exceeds the culvert diameter or height by more than 40 %) is intended, special foundations shall be installed under the pipes and end walls, and if, according to the filtration calculation, it is necessary to extend the filtration path, diaphragms shall be constructed, taking into account that:

48.1. the minimum diameter of a culvert in surface drainage trenches and contour ditches, if the culvert length does not exceed 10 m, is 0.3 m;

48.2. the minimum diameter of a culvert in diverting ditches and water drains is 0.5 m, if the culvert length does not exceed 10 m, and 0.8 m, if the culvert length is 10 to 15 m;

48.3. the mark of the roadbed surface shall be such as to ensure, depending on the material and dimensions of the pipe, the minimum pipe cover of 0.5 m and, in a non-pressure operation mode, it shall be at least 0.5 m higher than the estimated flow rate water level in the culvert, but in a partial pressure or pressure operation mode - at least 1.0 m higher than the water impounding level;

48.4. to reduce the risk of culvert silting, the longitudinal gradient of the culvert bottom shall be designed to be no less than 0.005 m and no less than the stream bed gradient of the bottom upstream of the culvert.

49. The mark of the underside of the span of bridges, footbridges, and plank-ways shall be at least 0.5 m above the estimated flow rate water level and 0.75 m above the highest water level during ice drift.

3.3. Boundary Grid

50. To enclose the agricultural land to be drained from surface runoff and incoming groundwater from surrounding areas (forest, bog, elevated relief areas), contour ditches and interceptor ditches shall be designed.

51. A contour ditch for intercepting surface runoff along the forest boundary shall be designed regardless of exposure of the forest to cardinal directions if the land surface rises upon entering the forest, but along the northern, north-eastern, and eastern edges of the forest also in cases when the land surface does not rise upon entering the forest.

52. An interceptor ditch shall be designed to capture groundwater in the alluvial area where it transitions to a surface elevation, on slopes and other relief break locations, as well as in places where artesian water is possibly present.

53. The contour ditch and the interceptor ditch shall be discharged directly into the diverting ditch, water drain, or water body and in certain cases also into a gully from which the runoff is conveyed to the diverting ditch via a separate collector drain.

54. The cross-sections of the contour ditch and the interceptor ditch shall be designed in a trapezoidal shape, with a bottom width of 0.4 m and a slope gradient coefficient m = 1.5, but in sand and loamy sand ground - m = 2.0. On a slope, the upper slope of the interceptor ditch may be made flatter, and the spoil heap on the lower side of the slope may be formed as a rampart.

55. The depth of the contour ditch and the interceptor ditch in mineral soils and shallow peatlands up to 0.8 m deep shall be designed in the depth from 1.1 to 1.2 m, in deep peatlands - from 1.2 to 1.3 m. If the depth of peat is from 0.8 up to 2.0 m, then the depth of the contour ditch and the interceptor ditch shall be designed up to the mineral soil base.

56. The longitudinal gradient of the bottom of the contour ditch and the interceptor ditch shall be designed within the range from 0.5 to 5.0 ‰.

3.4. Regulating (Detailed Drainage) Network

57. For the detailed drainage of agricultural land, a regulating (detailed drainage) network (drain or surface drainage trench systems) shall be designed.

58. The drain system shall consist of drainage pipes and collectors with drainage structures which collect excess soil water and convey it to the drainage network (diverting ditch, water drain, or water body).

59. Depending on the hydrogeological and topographical conditions of the area to be drained and the type of land use, systematic (continuous) or localised (selective) drainage shall be designed as follows:

59.1. for the drainage of uniformly overwetted bog soils, humic gley and gleyed mineral soils in conditions of little relief variation, systematic drainage shall be designed in which drainage pipes are arranged throughout the area to be drained at regular or nearly regular intervals;

59.2. in hilly terrain, for the drainage of inter-hill depressions, individual spring areas, and overwetted spots, localised drainage shall be designed in which drainage pipes are arranged irregularly, in separate groups with variable drain spacing, not covering the entire area to be drained.

60. In areas where inflow of surface water or groundwater from adjacent areas is expected, at spring or artesian water discharge sites, at the lower part or foot of slopes, and in places where the land surface gradient exceeds 3 %, cross-drainage shall be designed, i. e., so that the drainage pipes form a narrow angle with the contour lines of the relief.

61. In areas with a small average land surface gradient (up to 3 %), longitudinal drainage shall be designed so that the drainage pipes are approximately perpendicular to the contour lines of the relief.

62. The optimal longitudinal gradient of drainage pipes shall be from 1.0 to 1.5%. If the land surface gradient is greater than 0.5%, drainage pipes shall not be designed with the minimum (Table 2 of Annex 8 to this Building Code) or artificial longitudinal gradient.

63. Clay and polymer material (plastic) drain pipes shall be used for drainage. For the drainage of peat soils deeper than 1.5 m, wooden box or brushwood fascine drains may be used. Plastic pipe drains shall not be used in places where the concentration of iron compounds in the groundwater is greater than 3 mg/l.

64. Under normal hydrogeological conditions, 50 mm diameter clay or 63 (65) mm diameter plastic drainage pipes shall be designed. In places where inflow of artesian or surface water from adjacent areas is expected, in inter-hill depressions, at the foot of hills, and in spring areas, the diameter of drainage pipes shall be increased by one grade - by designing 75 mm diameter clay or 90 (80) mm diameter plastic drain pipes.

65. The spacing between drainage pipes shall be calculated depending on the mechanical composition of the soil to be drained and its physical and chemical properties:

65.1. in homogeneous mineral soils, the drain spacing E_p (m) shall be calculated, using the following formula:

E_p = E_n × K_ū × K_v × K_k × K_i, where (19):

E_n - normative drain spacing (m). In cohesive soils (clay, loam) E_n shall be determined, using the graph in Figure 1 of Annex 8 to this Building Code. In non-cohesive soils (sand, loamy sand) E_n shall be determined, using the Nomogram 2 of Annex 8 to this Building Code;

K_ū - the coefficient depending on the degree of water abundance in the relevant area (Map 1 of Annex 8 to this Building Code);

K_v - the complex coefficient of local conditions (Table 1 of Annex 8 to the Building Code);

K_k - the coefficient depending on the chemical properties of mineral soils (Table 2 of Annex 8 to this Building Code);

K_i - the coefficient depending on the type of use of mineral soils:

for arable land - 1.0;

for pastures - 1.1;

for meadows - 1.2;

for orchards - 0.6 to 0.7;

65.2. in layered soils, the standard drain spacing E_n (m) shall be determined, using the following formula:

En=	E1 × h1 + E2 × h2 + E3 × (h3 + 0.2)	, where (20):
	t - a+0.2

E₁ - the standard drain spacing (m) corresponding to the upper homogeneous soil layer;

E₂, E₃ - the standard drain spacings (m) corresponding to the other homogeneous soil layers;

h₁ - the thickness of the upper soil layer excluding the arable layer (m);

a - arable layer (m);

h₂, h₃ - the thicknesses of the other soil layers (m). 0.2 m shall be added to the thickness of the lowest layer;

t - drain depth (m) (t = a + h₁ + h₂ + h₃);

65.3. if the thickness of the homogeneous non-cohesive soil layer is less than the drain depth plus 0.2 m or if the terrain is hilly, then E_n (m) shall be determined, using Graph 1 of Annex 8 to this Building Code for cohesive mineral soils;

65.4. in peatlands with a peat layer thickness up to 0.6 m, the drain spacing E_p (m) shall be determined in the same way as for mineral soils, but taking into account the peat depth after its initial subsidence. If there is a low-permeability mineral soil beneath the peat and, after initial subsidence, the thickness of the peat layer is from 0.3 to 0.6 m, the nominal drain spacing determined for the bog base shall be adjusted by a coefficient from 1.1 to 1.2. If the peat depth after initial subsidence is 0.3 m or less, the nominal drain spacing determined for the bog base shall be accepted;

65.5. in peatlands with the thickness of the peat layer greater than 0.6 m, the drain spacing E_p (m) shall be determined, using the following formula:

E_p = E_n' × K_ū × K_h' × K_a' × K_k', where (21):

E_n' - the standard drain spacing (m) under atmospheric feeding conditions in lowland bogs which, depending on the botanical composition of the peat and with a poorly filtering mineral (clay, loam, loamy sand) base, is specified in Table 3 of Annex 8 to this Building Standard, but with a well-filtering mineral (gravel, coarse sand, sand) base (Table 4 of Annex 8 to this Building Standard);

K_ū - the coefficient depending on the degree of water abundance in the relevant area (Map 1 of Annex 8 to this Building Code);

K_h' - the coefficient depending on the hydrogeological conditions of the bog (Table 5 of Annex 8 to this Building Code);

K_a' - the coefficient depending on the hydrological conditions of the bog (Table 6 of Annex 8 to this Building Code);

K_k' - the coefficient depending on the concentration of iron compounds in the bog groundwater (Table 7 of Annex 8 to this Building Code).

66. In hilly terrain, the calculated drain spacing shall be differentiated depending on the land surface gradient, the mechanical composition of the soil, the degree of gleying, and the type of land use. In sand and loamy sand ground without signs of gley, drainage shall not be designed.

67. Drain systems shall be designed according to the arrangement of drainage system elements indicated in Table 8 of Annex 8 to this Building Code in relation to the calculated mutual spacing E_p of the drainage pipes.

68. Drainage pipes shall be connected to the collector as vertically as possible, but at an angle of no less than 60°.

69. Drain collector routes shall be designed straight, without unnecessary bends, along the shortest route to the diverting ditch, water drain, or water body.

70. Drain pipe routes in the vicinity of trees and shrubs shall be routed in order to ensure the following minimum distances:

70.1. 30 m - up to coniferous trees;

70.2. 20 m - up to broadleaved trees;

70.3. 15 m - up to willows, osiers, alders;

70.4. 10 m - up to other shrubs and berry bushes;

70.5. 7 m - up to fruit trees.

71. The construction depth of the collector must ensure the possibility of connecting drainage pipes at the designed depth. Above the surface of the collector pipe, there shall be at least 0.9 m of soil cover, and above a large-diameter collector - 0.8 m.

72. At crossings of the drain collector with other pipelines, the gap between the pipes in the vertical plane shall be at least 0.3 m. When crossing a road or other shallow ditch with a collector, the gap between the top of the collector pipe and the bottom of the ditch shall be at least 0.6 m.

73. The designed drain depth and spacing shall ensure the optimal groundwater depth required for field cultivation and the proper development of agricultural crops according to the drainage requirements. The average designed drainage requirements (m) for different types of land use are specified in Table 9 of Annex 8 to this Building Code. The lower values of the drainage requirements shall apply to sand and loamy sand ground, and the higher values - to clay soils and peatlands.

74. The construction depth of the drain shall be the vertical distance between the land surface and the level of the bottom edge of the drain. The average construction depth of drainage pipes, depending on the type of land use, soil composition, and water content coefficient, is specified in Map 1 of Annex 8 to this Building Code.

75. For the dimensioning of drain systems by means of hydrological calculations, the water conveyance intensity - runoff modules - shall be determined as follows:

75.1. the drain runoff modules for arable land and pastures (l/s × ha) are specified in Map 1 of Annex 9 to this Building Code. The value of the drain runoff module for meadows shall be determined as 80% of that specified for arable land. In inter-hill depressions without significant artesian water inflow, the drain runoff module specified in the map shall be increased by 20 %;

75.2. surface runoff from agricultural land shall be calculated depending on the catchment area of the receiving structure and the maximum daily precipitation intensity with a 10 % exceedance probability. The precipitation intensity for arable land (l/s × ha) is specified in Map 2 of Annex 9 to this Building Code. The surface runoff module (l/s × ha) for arable land, depending on the mechanical composition of the soil and the average land surface gradient of the catchment area, shall be determined, using Table 1 of Annex 9 to this Building Code. The surface runoff module from meadows and pastures shall be determined as 70 %, and from forest and bog - as 60 % of that specified for arable land;

75.3. surface runoff from areas with low-permeability surfaces (asphalt, concrete, paving, etc.) and from the roofs of buildings and structures shall be calculated by using the numerical value of precipitation intensity (l/s × ha) specified in Map 2 of Annex 9 to this Building Code, multiplying it by the area of the covered surface (ha) and by a coefficient of 0.85.

76. By means of the graphical-analytical or analytical calculation method for the hydraulic calculation of the drain system collector, depending on the determined runoff modules and using special nomograms or tables for the hydraulic dimensioning of drains, such drain parameters (cross-section and stream bed gradient) shall be selected as to ensure timely removal of drain and surface runoff in an optimal flow regime:

76.1. the maximum permissible flow speed in drain pipes in non-cohesive soils shall be 1.5 m/s and in cohesive soils - 2.0 m/s;

76.2. the minimum longitudinal gradients of drainage pipes and collectors are specified in Table 2 of Annex 9 to this Building Code;

76.3. the longitudinal gradient of large-diameter drain collectors shall ensure a flow speed of no less than 0.30 m/s.

77. In order to protect drain pipes from mechanical silting under all possible construction conditions and throughout the service life of the drainage and in order to ensure sufficiently intensive water inflow into the drain, the drain pipes or their joints shall be covered with a natural or synthetic filtering material in conformity with the following:

77.1. synthetic filter material shall not be used in clay, loam, and peat soils, as well as when constructing drains in water-saturated flowing soil;

77.2. plastic drain pipes wrapped with straw may be used in clay, loam, and peat soils, but shall not be used in sand soils;

77.3. synthetic material film shall not be used as bedding under clay drain pipes.

78. If the groundwater in the area to be designed has an increased concentration of bivalent iron compounds, additional measures shall be taken to prevent clogging of clay pipe drains with iron compounds:

78.1. if the concentration of iron compounds is from 3 to 8 mg/l, then:

78.1.1. the minimum longitudinal gradient of the drains shall be increased to at least 0.4 %;

78.1.2. the longitudinal gradient of the drain collector in the downstream section of 10 to 15 m in length shall be increased to at least 1.0 %;

78.1.3. the mutual spacing of the drains shall be reduced by 10 %;

78.2. if the concentration of iron compounds in the groundwater is greater than 8 mg/l, it shall not be recommended to design drainage. Drainage may be ensured, using previous drainage ditches, and only after three to five years if the concentration of iron compounds has decreased below 8 mg/l, drainage may be designed.

79. In order to ensure normal operation and control of the drain system, drainage structures (drain outlets, drain wells, gullies, filters, surface water receivers, and other structures) shall be designed in conformity with the following:

79.1. for the discharge of the waters of each drain system into a diverting ditch, water drain, or water body, a drain outlet shall be used;

79.2. drain wells shall be designed in the following cases:

79.2.1. if more than three collectors are connected within one node of the drain system;

79.2.2. if the collector route turns by more than 60°;

79.2.3. if the water flow speed in the collector decreases to the minimum permissible speed;

79.2.4. every 500 metres if the collector is longer than one kilometre;

79.3. the height of the aboveground part of an open drain well shall be at least 0.2 m, but no more than 0.5 m;

79.4. above the cover of a covered well, there shall be a soil layer at least 0.6 m in thickness;

79.5. in heavy, low-permeability soils, filter columns, filters, drain embedments, or drain trench backfills made of well-filtering materials (for example, wood chips, light-expanded clay aggregates, gravel, straw) shall be used in local land surface depressions;

79.6. in places with particularly pronounced, intensive groundwater inflow, drain trenches shall be backfilled to the thickness of the water-bearing layer with gravel or wood chips, and drains shall be covered with fascine or compressed straw bales;

79.7. for the collection of surface runoff from shallow, pronounced relief depressions in the areas to be drained and for its introduction into the drain system, surface water collectors shall be designed;

79.8. for the conveyance of surface waters into surface water bodies, reinforced chutes shall be designed.

80. Surface drainage trench systems or individual surface drainage trenches shall be designed as temporary if preliminary drainage of the areas is required (Paragraph 17 and Sub-paragraph 78.2 of this Building Code).

81. In sand and loamy sand soil and in peat bogs up to 2 m deep on a mineral soil base, surface drainage trench systems may lower the groundwater level in the soil with sufficient intensity; however, in heavy, low-permeability mineral soils, the main task of surface drainage trenches shall be to collect and convey the surface runoff into the diverting ditch.

82. Surface drainage trenches shall be designed obliquely to the relief contours so that the ditch crosses the main direction of surface water flow and groundwater flow.

83. The minimum longitudinal slope of surface drainage trenches shall be 0.5 ‰, whereas the maximum - 5 ‰.

84. The bottom width of surface drainage trenches shall be 0.4 m, the maximum length shall be 1500 m, but the main parameters shall be selected depending on the relief, situation, and soil conditions of the area to be drained in accordance with Table 3 of Annex 9 to this Building Code. The average depth of surface drainage trenches in peat bogs shall be determined, taking into account the subsidence of the peat layer.

3.5. Surface Runoff Regulation

85. By regulating surface runoff, the faster conveyance of surface waters from the areas to be drained into the regulating and boundary grid, water drain, diverting ditch, or water body and infiltration into the soil base layer shall be promoted; the possibility of water accumulation in depressions and other low-lying parts of the area to be drained shall be prevented, and soil compaction shall be reduced.

86. When carrying out the grading of areas, the creation of surface runoff furrows, the filling of small closed depressions, pits, ditches, oxbows, and the levelling of boundary lines and steep banks, it shall be ensured that, after soil movement and settlement, the designed drain depth is maintained.

87. When creating runoff furrows, the possibilities for land cultivation and drain systems shall be assessed, the slopes of the furrow sides shall be formed with a gradient of 1:10 or flatter, a longitudinal slope of no less than 0.1 %, and a depth no greater than 0.4 m. The routes of runoff furrows shall not coincide with the routes of drain collectors.

88. Subsoil deep loosening shall be suitable in heavy gleyed clay and loam soils with a filtration coefficient less than 0.2 m/d, in depressions of mineral soil with hilly relief, and in soils with an ortstein horizon.

89. Deep loosening may be carried out after the construction of drains and when the soil has an optimal moisture content:

89.1. the working direction of the deep loosener shall be perpendicular to the direction of drainage pipes, and the spacing between the slits in clay and heavy loam soils and soils with an ortstein horizon shall be 0.8 m, in other soils - 1.6 m;

89.2. the loosening depth shall be at least 0.2 to 0.3 m less than the drain depth.

3.6. Dual-operation Land Amelioration Systems

90. In order to create the optimal air and moisture regime for crops in the active soil layer during the vegetation period in areas to be drained, drainage systems may be used for groundwater level regulation, and dual-operation land amelioration systems may be constructed.

91. Dual-operation land amelioration systems shall be designed:

91.1. in flat areas where the land surface gradient is less than 0.5 ‰;

91.2. in sand, loamy sand, and lowland bog peat soils where the filtration coefficient is greater than 0.5 m/d;

91.3. if it is possible to provide water resources of at least 0.5 l/s × ha during the low-water period.

92. Depending on the water resources available for irrigation, soil permeability, and crops to be grown, subsoil moistening with dual-operation land amelioration systems may be carried out:

92.1. by maintaining the groundwater level conditionally constant throughout the vegetation period;

92.2. by cyclically raising and conveying water, maintaining an elevated groundwater level periodically from three to six times during the vegetation period.

93. The optimal groundwater level (m) to be maintained in the drained area during the vegetation period by raising the water may be determined, using the data in Table 4 of Annex 9 to this Building Code.

94. In case of cyclic groundwater level regulation, the water level shall be raised to 0.3-0.4 m above the land surface and maintained unchanged for three to four days.

95. If, during the summer half-year, the flow in the diverting ditch is sufficiently high, by constructing water level retention structures therein, it shall be possible to raise the water level and to introduce water into the regulating network either continuously throughout the vegetation period or cyclically. Water from the regulating network through the joints or perforations of the drain pipes and the beds of the surface drainage trenches, under the influence of pressure, shall infiltrate into the soil and raise the groundwater level to the optimal depth.

96. The minimum 30-day flow in the diverting ditch during the summer half-year with a 75 % exceedance probability Q (l/s) shall be greater than the water consumption of crops and evaporation from the soil which is characterised by the average daily irrigation hydromodule q_m (l/s × ha) (Table 1 of Annex 10 to this Building Code):

Q ≥ q_m × F, where (22):

F - area to be moistened (ha).

97. If, during the summer half-year, the inflow in the diverting ditch is insufficient to raise the groundwater level, the required water shall be supplied from a water source - a watercourse or water body. For the supply of water, a gravity pipeline or pressure pipeline shall be designed.

98. In order to use the regulating network of the drainage system for groundwater level regulation:

98.1. the diameter of the drain pipes shall be increased by at least one grade;

98.2. the spacing between the drainage pipes and surface drainage trenches shall be reduced by 30 to 40 %;

98.3. the length of the drainage pipes shall be reduced up to 150 m;

98.4. the perimeter of the drain pipes shall be covered with a filtering material along their entire length;

98.5. water level regulation structures shall be installed in diverting ditches, surface drainage trenches, or drain wells;

98.6. materials that allow for prolonged inundation shall be used for the reinforcement of beds;

98.7. observation wells (boreholes) shall be installed for monitoring groundwater levels.

3.7. Irrigation Systems

99. Irrigation systems shall be designed to optimise the soil moisture and nutrient regime required for the development of agricultural crops, primarily vegetables, cultivated grasslands, and intensive fruit and berry crops during the vegetation period.

100. During periods of moisture deficit in the vegetation period, the water required for crop development (with or without dissolved nutrients) may be supplied by special equipment or machinery, either by spraying artificial rain (irrigation) or by supplying water at low intensity through a network of small-diameter pipes via special water outlets - drippers - directly into the root zone of the plants (drip irrigation).

101. The required irrigation regime of the irrigation system - irrigation rates and timing - shall be determined for an average dry vegetation period in which the climatic water consumption deficit is calculated with a 75 % exceedance probability, taking into account that:

101.1. irrigation requirements depend on the intensity of evaporation and transpiration, the amount of precipitation, the moisture reserves in the soil at the beginning of the vegetation period, soil properties, agrotechnics, and the characteristics of the crop;

101.2. the timing and rates of irrigation depend on the moisture deficit during the vegetation period, the biological characteristics of the irrigated crops, and the moisture capacity of the active soil layer;

101.4. the average irrigation requirements of agricultural crops in various agroclimatic regions of Latvia (Map 1 of Annex 10 to this Building Code) are summarised in Table 1 of Annex 10 to this Building Code, but in each specific case they are determined by the water balance equation of the active soil layer.

102. Watercourses, water bodies, or groundwater resources with sufficient water resources may be used as a water source for the irrigation system, provided that:

102.1. for crop irrigation, water with a mineralisation level of up to 1.5 mg/l, an active reaction (pH) above 5.5, and a water temperature above 10° C may be used without restrictions;

102.2. the suitability of water for crop irrigation is also determined by the ratio of sodium to calcium cations in milliequivalents which must be less than one;

102.3. the drip irrigation system includes special filters for separating fine mechanical impurities and hydrobionts (e.g., algae) from the intake water, as well as, where necessary, special devices for reducing iron hydroxide, carbonates, and other salts in the water.

103. The type of water intake structure shall depend on the water source, the chosen irrigation method, and the equipment. The pumping station shall ensure the supply of water at the required pressure according to the water consumption of all simultaneously operating irrigation devices or drippers, including losses in the supply network. The maximum pressure developed by the pumps shall not exceed the permissible pressure for the pressure pipes.

104. The water consumption of the irrigation system Q_s (l/s) shall be determined, using the following formula:

Qs =	24 × F × qm	, where (23):
	t × k

F - system area (ha);

q_m - average daily irrigation hydromodule (l/s × ha) the values of which are determined in accordance with Table 1 of Annex 10 to this Building Code;

t - system operating time (h);

k - equipment utilisation time coefficient.

105. Irrigation systems, depending on the type of pumping stations, pressure pipelines, and irrigation equipment used, shall be designed as stationary, semi-stationary, or mobile systems:

105.1. in mobile systems, all elements, including the pumping station, are mobile;

105.2. in semi-stationary systems, one of the main elements of the system may be stationary;

105.3. in stationary systems, all system elements are stationary.

106. Depending on the working pressure, capacity, jet range, and type of spraying required for the irrigation equipment, the material and layout of the irrigation system supply network shall be selected.

107. The water supply network of stationary irrigation systems shall be designed according to a hydraulic calculation as a pressure pipeline with the necessary fittings (hydrants, gate valves, water outlets, non-return valves, safety valves, water meters, and other fittings) in conformity the following requirements:

107.1. all branches of the pressure pipeline shall be equipped with gate bolts;

107.2. at points of change in elevation of the pressure pipeline in the vertical plane, where air accumulation in the pipe is possible, air release valves shall be provided;

107.3. for emptying the pressure pipeline, water outlets shall be designed at the lowest points of the pipeline, and its longitudinal slope in the direction of the outlet shall be greater than 0.1 %;

107.4. if the turning angle of the pressure pipeline in the horizontal or vertical plane, as well as at the ends of the pipelines exceeds 10°, concrete supports shall be designed;

107.5. if the calculated pressure in case of hydraulic shock exceeds the permissible value for the relevant pipeline, anti-shock valves shall be installed;

107.6. the height of the hydrant for connecting irrigation devices shall be ensured in accordance with the requirements of the device to be connected but, if hydraulically extendable hydrants are not used, it shall not be less than 0.5 m above the land surface.

108. When designing the layout of the irrigation system, the necessary safety zone along power lines shall be ensured. The water jets of irrigation equipment, taking into account possible wind-induced deviation, shall not allow droplets to fall closer than 10 metres from the horizontal projection on the land surface of the outer conductor of a 20 kV power line and not closer than 20 metres from a higher voltage power line.

109. When designing drip irrigation systems, the calculated daily water supply volume W (m³/d) shall be determined, using the following formula:

W = 0.864 × q_m × F × P, where (24):

q_m - average daily irrigation hydromodule (l/s × ha) in accordance with Table 1 of Annex 10 to this Building Code;

F - area of the irrigation system (ha);

P - proportion of the irrigation system area in which the plant root zone is located, determined as the area of the projection of the aboveground parts of the plants onto the land surface (%). If the aboveground parts of the plants completely overlap the entire area, then P = 100 %. In intensive orchards (for example, containing dwarf apple, plum trees, cherry trees), P ranges from 30 to 60 %.

110. Water consumption Q of the drip irrigation system_s (l/s) shall depend on the area of the system, the arrangement, number, and flow rate of the drippers which shall ensure moistening of at least 25 % of the plant root zone area.

111. In drip irrigation systems, main, distribution, and irrigation pressure pipelines shall be designed from polymer material pipes. Downstream of the system filter on the pipeline, the use of corrosion-prone metal fittings and valves shall not be permitted. For connecting pipes, plastic compression fittings, weldable plastic fittings (for polyethylene pipes), or adhesive fittings (for polyvinyl chloride pipes) shall be used.

112. The layout of the drip irrigation pressure pipeline network shall be determined depending on the topographical conditions of the area, the arrangement of irrigated crops, the number of irrigation subsystems, the required working pressure, and the flow rate. The system parameters shall be determined by hydraulic calculation of the pipelines.

113. The main pipelines in semi-stationary drip irrigation systems and also the distribution pipelines in stationary systems shall be constructed underground, ensuring the emptying and venting of the pipelines. The minimum depth of pipeline construction from the land surface to the top of the pipe shall not be less than 0.8 m. Dripper pipes shall be placed in the planting rows above the land surface, but in mulched areas - also under the mulch.

4. Forest Land Drainage Systems

114. Forest land drainage systems shall ensure a technically and silviculturally justified, site- and forest-type-specific degree of drainage, whereby the drainage effect does not decrease by more than one site quality class with increasing distance from the main surface drainage trench and which shall ensure the establishment of the necessary forest infrastructure, including the required network of forest roads.

115. The formation of the forest road routes and roadbeds shall be designed simultaneously with the design of the regulating drainage network.

4.1. Regulating Network

116. The regulation of moisture in forest land shall be ensured by the regulating network - surface drainage trenches, runoff furrows, and road ditches. In areas of deep peat and springs or in closed depressions, it shall be recommended to excavate temporary drainage ditches - pioneer ditches - prior to the construction of the permanent regulating network.

117. The routes of surface drainage trenches shall be designed, assessing the following:

117.1. forest growth conditions and forest types;

117.2. forest management elements (for example, compartment block rides, felling site directions, timber transportation possibilities);

117.3. relief;

117.4. soil and hydrogeological conditions;

117.5. the existing hydrographic network;

117.6. the existing and planned road network.

118. Within the boundaries of wood compartments, surface drainage trenches shall be designed up to the compartment block rides and shall be directed into the diverting ditch or road ditch running along the highest edge of the firebreak:

118.1. in order not to impede surface runoff, the spoil heap of the ditch shall be formed on the lower side of the surface drainage trench and shall be brought closer to the road or the carriageway of the compartment block ride;

118.2. the surface runoff shall be conveyed through the ditch spoil heap by means of pipes or fascines.

119. In forest clearings and in low-permeability soils, runoff furrows shall be designed to facilitate faster conveyance of thaw and precipitation water along the lowest points of the relief to the surface drainage trenches.

120. The mutual distances (m) between surface drainage trenches shall be determined differentially depending on forest growth conditions and forest type, soil and hydrogeological conditions in order to ensure a similar degree of drainage within the same site quality class in accordance with Table 1 of Annex 11 to this Building Code.

121. The average depth (m) of surface drainage trenches shall be determined depending on soil conditions in accordance with Table 2 of Annex 11 to this Building Code.

122. The depth of surface drainage trenches in peatland after peat settlement shall not be less than 1 m.

123. The bottom width of surface drainage trenches shall be 0.4 m, and the slope gradient coefficient shall be determined in accordance with Table 3 of Annex 11 to this Building Code.

124. The minimum longitudinal gradient of the bottom of surface drainage trenches shall be 0.5 ‰.

125. Surface drainage trenches shall be connected to the diverting ditch at an angle of 60 to 90°, and the connection shall be formed with a curve for which a radius of approximately 5 m is assumed.

126. The average depth of runoff furrows shall be designed to be 0.4 m.

127. The parameters of road ditches shall be designed according to the parameters of surface drainage trenches. However, if it is necessary to provide soil for the formation of the roadbed, the width or depth of the road ditch may be increased.

4.2. Boundary Grid

128. Contour ditches shall be designed along the contour of the area to be drained, with parameters corresponding to those of surface drainage trenches.

129. In peatlands with a peat depth of less than 2 m, the bottom of the contour ditch shall be deepened into the mineral soil base.

4.3. Drainage Network and Water Drains

130. For diverting ditches of small basins (where the catchment area is less than 0.5 km²), the bed bottom width shall be designed to be 0.4 m, with a slope gradient coefficient m = 1.5. For larger diverting ditches and water drains, the cross-section shall be determined by hydraulic calculations (Paragraph 23 of this Building Code).

131. In order to ensure the stability of the beds of diverting ditches and water drains, the bottom longitudinal gradients shall be designed to be as uniform as possible over the longest possible section, and the calculated stream velocity shall be verified. In forest land, the calculated stream velocities in the beds may be higher than in similar beds in agricultural land:

131.1. the permissible maximum stream velocities in unreinforced beds of forest land with a hydraulic radius of less than 0.5 m are specified in Table 4 of Annex 11 to this Building Code;

131.2. the permissible maximum stream velocities in reinforced beds are specified in Table 2 of Annex 7 to this Building Code;

131.3. in the curves of diverting ditches and water drains, the permissible maximum stream velocities shall be reduced by 20 %.

132. The bends in routes of diverting ditches and water drains shall be formed with a curve the minimum radii of which, depending on the hydraulic radius, may be accepted in accordance with Table 5 of Annex 11 to this Building Code.

133. The stability of the beds of diverting ditches and water drains shall be verified by calculating the stream velocity at the maximum spring tide flow rate with a 5 % exceedance probability.

5. Peat Deposit Drainage Systems

134. Peat deposit drainage systems shall be designed in order to ensure suitable conditions for drying the upper loosened layer of the peat deposit, as well as the groundwater level required for the operating field preparation, peat extraction and transportation mechanisms - according to the drainage requirements.

135. Depending on the type of peat deposit and the method of extraction, the average drainage requirements shall be assumed as follows:

135.1. in raised bogs (by the layer extraction method) - 0.8 to 1.0 m;

135.2. in lowland and transitional bogs - 0.6 to 0.8 m.

136. The drainage of the peat deposit shall be ensured by a regulating network - peat field ditches, and also surface drainage trenches, road ditches, and drainage.

137. The regulating network shall be designed, assessing the following:

137.1. the nature of the relief of the bog surface and the mineral soil base;

137.2. the configuration of the deposit and the existing hydrographic network;

137.3. the hydrogeological conditions of the bog;

137.4. the technological scheme of peat extraction.

138. Peat field ditches for draining peat deposits in raised and transitional bogs shall be designed with an average distance between the axes of the peat field ditches of 20 m, an average depth after bog subsidence 1.7 to 1.8 m, a bottom width 0.3 to 0.4 m, and a slope gradient coefficient of 0.25.

139. Peat field ditches for draining peat deposits in lowland bogs shall be designed with an average distance between the axes of the peat field ditches of 40 m, an average depth after bog subsidence 1.4 to 1.6 m, a bottom width 0.3 to 0.4 m, and a slope gradient coefficient 0.25 to 0.5.

140. The minimum longitudinal gradient of the bottom of peat field ditches shall be 0.3 ‰.

141. The length of peat field ditches shall depend on the peat extraction and transportation technology. In milled peat fields, the optimum length of peat field ditches shall be 500 m.

142. For the drainage of peat stockpiles and road strips, drainage with an average construction depth of 1.8 m, an average distance between drainage pipes in raised and transitional bogs 10 to 12 m, and in lowland bogs 20 to 24 m is recommended to be designed.

143. For the collection and conveyance of water from peat field ditches and contour ditches to the diverting ditch, collecting ditches shall be designed with an average depth after peat subsidence from 2.3 to 2.5 m, a bottom width from 0.4 to 1.0 m, a slope gradient coefficient in raised and transitional bogs 0.5 to 0.75 and in lowland bogs 0.75 to 1.0:

143.1. the minimum longitudinal gradient of the bottom of collecting ditches shall be 0.5 ‰;

143.2. for the retention of suspended peat particles in the lower part of collecting ditches, a sedimentation basin shall be constructed with a minimum deepening of 0.7 m below the ditch bottom, a length of 50 m, and a surface width from 15 to 20 m.

144. For culverts in peat field ditches, plastic pipes, clay drain pipes (on a wooden mat) with a nominal diameter of 100-150 mm, or wooden boxes of 100 × 150 mm shall be used. A wire screen with the maximum mesh size of 30 × 30 mm shall be installed at the upstream end of the culvert.

145. Diverting ditches, water drains, and the boundary grid shall be designed in accordance with the regulations regarding the design of drainage for forest land.

146. In deep raised bogs, peat field ditches, drain construction trenches, collecting ditches, contour ditches, and diverting ditches are recommended to be constructed in several excavation stages by digging preliminary drainage starter trenches.

6. Territorial Engineering Protection and Polder Systems

147. Engineering protection and polder systems shall be designed for protecting against flooding or overwetting populated areas, agricultural and forest land, and other existing territories in alluvial areas of watercourses, on the shores of the sea, or the banks of water bodies.

148. The causes, nature, and duration of flooding or overwetting of territories, the intended use of the territory and economic efficiency shall determine the engineering protection measures to be designed (regulation of the watercourses, colmatage of the territory, drainage or establishment of a polder):

148.1. by regulating the watercourse - straightening and deepening the bed - it is possible to control alluvial area flooding, the amount of deposited sediment and to accelerate the conveyance of water from the flood-plain in the alluvial area period (Sub-section 3.2 of this Building Code);

148.2. if it is not possible to ensure the necessary conditions for the use of the territory by regulating the watercourse or if it is not expedient from the point of view of environmental protection, the territory shall be enclosed by protecting dikes, with the interception, conveyance, or detailed drainage of filtration and surface waters;

148.3. if the drainage of such territories and the abstraction of incoming waters requires mechanical lifting of water either permanently or during certain periods, a polder shall be designed.

6.1. Protecting Dikes

149. By damming a watercourse or water body, the alluvial area or adjacent territories can be protected from complete flooding (non-flooded protecting dikes) or from flooding during summer-autumn floods, allowing the area to be flooded during the spring tide (flooding protecting dikes).

150. The height of protecting dikes above the estimated water level shall be calculated, taking into account the wind-induced surge height, the wave run-up height on the dike slope, and the height reserve of the protecting dike:

150.1. the estimated water level for a non-overflowing protecting dike shall be determined as the water level in the watercourse at the maximum flow rate of spring tide with a 1 % exceedance probability, and the height reserve of the dike shall be assumed as 0.5 m;

150.2. the estimated water level for an overflowing protecting dike shall be determined depending on the purpose of use of the protected territory, and the height reserve of the dike shall be assumed as 0.3 m, except in the cases specified in Paragraph 154 of this Building Code.

151. The throughput capacity of the bed of a dammed watercourse shall be calculated, using the formulas for non-uniform hydraulic flow, and the narrowed active cross-section, altered water levels, and stream velocities shall be determined in the dammed section, as well as downstream and upstream of the dammed section.

152. The minimum distance of the protecting dike from the watercourse bed shoreline in stable mineral soils shall be at least 5 m, in unstable mineral soils and peat - at least 10 m, but no less than twice the height of the protecting dike.

153. The cross-section of the protecting dike shall be designed as trapezoidal, with slopes of varying gradients and a crest width of at least 3 m. If also a road is planned on the protecting dike, the crest width of the dike shall be determined according to the type of road:

153.1. the average gradient of slopes for protecting dikes up to 3 m in height shall be determined on the basis of Annex 12 to this Building Code;

153.2. for protecting dikes higher than 3 m or those permanently washed by water, stability and filtration calculations of the dike cross-section shall be performed;

153.3. the stability of wet slopes of protecting dikes shall be verified for permissible stream velocities (Paragraph 28 of this Building Code);

153.4. the dry slopes of protecting dikes shall be protected from the effects of precipitation by reinforcing it by sowing grass, turfing or using other anti-erosion materials.

154. In suitable locations of flooding protecting dikes, special regulators or specially reinforced lowered sections of the dike shall be installed through which water can be introduced into the protected area at the beginning of the flood phase and discharged at the end of the flood phase.

6.2. Collection and Conveyance of Filtration and Incoming Surface Waters

155. In order to lower the artificially raised groundwater level in areas adjacent to the water reservoir and to protect them from overwetting, a bank drain, interceptor ditches, or systematic drainage of the area shall be designed.

156. The bank drainage shall be constructed along the edge of a water reservoir as a single drain or several drains with a filter material embedment above the drain.

157. The construction depth and diameter of the drain pipes, depending on the soil filtration properties, shall be determined by calculating the intensity of filtration water inflow:

157.1. the minimum diameter of drain pipes shall be 100 mm;

157.2. the maximum construction depth of drain pipes shall be determined depending on the pipe material.

158. Manholes shall be created at the bends of a drain pipe and at intervals of no more than 50 m in straight sections.

159. In suitable hydrogeological conditions, vertical drainage may also be used by constructing boreholes or a row of wells along the water reservoir bank from which the incoming water is pumped out.

160. An interceptor ditch may be constructed along the water reservoir bank for the collection and conveyance of filtration waters and surface runoff waters (Paragraphs 50, 51, 52, 53, 54, 55, and 56 of this Building Code).

161. Low-permeability soils in areas adjacent to the water reservoir may be drained by systematic drainage, reducing the designed drain spacing or increasing the drain diameter near the bank (Paragraph 64 of this Building Code).

162. The water collected by the bank drainage, interceptor ditches, or drain system shall be discharged into the lower reach of the water reservoir or pumped into the water reservoir.

163. If water flows onto the alluvial area or areas adjacent to the water reservoir from relatively higher areas, it may be rained by a bypass channel outside the protected areas and discharged into the lower reach of the water reservoir or another water drain.

6.3. Polders

164. The drainage system of a polder shall include flood protection dikes, bypass channels, a storage basin, a boundary and regulating grid, a pumping station, and regulators. The polder system may comprise all the structures referred to in this Paragraph or only some of them, but shall consist of at least flood protection dikes and a pumping station.

165. Depending on the protected territories, polders shall be classified as follows:

165.1. coastal polders - protect coastal territories from sea surges;

165.2. alluvial area polders - protect the alluvial areas of watercourses or territories adjacent to water bodies from spring tide or summer-autumn flood waters;

165.3. lowland polders - protect territories adjacent to water reservoirs from the impact of impounded water levels in the water reservoirs. This also shall include engineering protection systems, and also flood-free territories the drainage waters of which are conveyed by pumping.

166. Depending on the hydrological regime, polders shall be classified as follows:

166.1. winter (non-flooded) polders the areas of which are completely enclosed by protecting dikes to protect from the estimated spring tide water levels. The estimated water level shall be accepted as the maximum spring tide water level with a 1 % exceedance probability in the watercourse or water body or the highest sea surge water level observed over a long-term period;

166.2. summer (flooded) polders the areas of which are enclosed by protecting dikes from the estimated summer-autumn flood water levels. The estimated water level shall be accepted as the maximum summer-autumn flood water level with a 5 % exceedance probability, if the polder areas are used for the cultivation of spring crops, vegetables, technical or fodder crops, and with a 10 % exceedance probability, if the areas are used for meadows and pastures. Flooding of areas during the spring tide is expected.

167. The amount of water to be pumped by the winter polder pumping station shall be determined by analysing the spring tide water balance with a 10 % exceedance probability, assessing the inflow intensity, volume, the possibilities for water to accumulate in the soil of the polder basin, in beds and terrain depressions and allowing for a limited operation (insufficient drainage) period of the polder drainage systems 7 to 10 days in arable land and 10 to 14 days in meadow and pasture areas.

168. The amount of water to be pumped by the summer polder pumping station shall be determined by the duration of the spring flood recession phase in the water drain or by the summer-autumn flood runoff with a 10 % exceedance probability from the polder area. In the calculation of the pumping station capacity, the most unfavourable case shall be assumed. In the calculation, limited operation of the polder drainage systems shall not be permitted.

169. The selection of pumps shall be determined by the calculated amount of water to be pumped and the maximum geodetic head of the pumps which is defined as the difference between the maximum estimated water level in the watercourse (water body, sea) and the lowest operational water level in the polder storage basin:

169.1. the highest operational water level in the polder shall ensure the required drainage standard at any point of the usable polder area. The highest operational water level shall be the water level in the polder storage basin at the pumping station when pumping begins (the pumps are switched on);

169.2. the lowest operational water level shall be the water level in the polder storage basin at the pumping station when pumping is stopped (the pumps are switched off).

170. In order to avoid instability of the slopes of the storage basin and the drainage network structures, the pumping capacity and operating regime shall ensure gradual rate of water level reduction in the storage basin and the drainage network. The rate of water level reduction shall not exceed 0.1 m/h.

171. For the accumulation of low-water period runoff from the polder basin and for optimising the operating regime of the pumping station, a pumping station storage basin shall be designed. Natural depressions, water bodies, specially excavated basins, or the widening and deepening of a section of the main diverting ditch bed near the pumping station may be used as a storage basin.

172. The useful volume of the storage basin V (m³) shall be calculated, using the following formula:

V = 0.25 × t_c ×Q, where (25):

t_c - the shortest permissible pump operating cycle (s);

Q - the capacity of the smallest pump at the pumping station (m³/s).

173. If soil conditions permit, the bottom level of the storage basin shall be designed at least 1.5 m below the lowest operational water level in order to prevent intensive overgrowth of the storage basin with aquatic plants and to promote sediment deposition.

174. The slopes of the storage basin shall be designed to be flatter than those of the water drain or diverting ditch, with an average slope gradient of at least 1:3. The slopes above the highest operational water level may be stabilised with grass seeding or turfing.

175. The bottom line of the storage basin shall be designed without longitudinal gradient, with a minimum bottom width of at least 4 m.

176. The inlets of the diverting ditches into the storage basin shall be introduced above the highest operational water level. The connection between the storage basin and the main diverting ditch in the interval between the highest and lowest operational water levels shall be designed over a section in the length of 20 to 30 m, and this section shall be reinforced.

177. In order to reduce bed silting and deformations in summer polders during inundation, the routes of diverting ditches and surface drainage trenches shall be designed in the direction of spring flood water flow, and the calculated drain spacing shall be reduced on average by 10 to 15 %.

178. In summer polders, the design shall provide for floodwater inlets-outlets or special water overflow sections in the protecting dike (Paragraph 154 of this Building Code). In water overflow sections, the crest level of the protective embankment shall be designed 0.2 to 0.3 m lower, while the embankment slopes shall be gentle (on average 1:8 to 1:20) and reinforced.

179. The water inlet and outlet throughput capacity Q (m³/s) shall be calculated, using the following formula:

Q = 2.5 × V / t, where (26):

V - the volume of water to be introduced into the polder (m³) - up to the crest level of the protective embankment;

t - the time in seconds during which the water level rises in the watercourse or water body from the water inlet threshold level up to the crest level of the protective embankment.

7. Drainage Systems of Populated Areas

180. In order to ensure a groundwater level in populated areas which is appropriate for the functional zoning and permitted use specified in the territorial plan, the design shall provide for the enclosure of the relevant territories or zones from incoming surface waters, lowering of the groundwater level, or land colmation, and also, if the territory is located in alluvial areas of watercourses, on the seashore or on the shores of water bodies - the measures specified in Chapter 6 of this Building Code:

180.1. in the built-up areas of populated places, the groundwater level shall be at least up to 2 m, and in the areas of stadiums, parks, squares and other green spaces - at least up to 1 m depth from the designed land surface level;

180.2. in populated areas, especially those with high building density, developed storm drain networks, and reinforced surfaces, the rainwater runoff may exceed the spring flood runoff volume calculated for determining the parameters of land amelioration systems and surface water bodies. In such territories, the rainwater runoff volume shall be additionally calculated, compared with the spring flood runoff volume, and the greater of the two shall be adopted;

180.3. the estimated flow rate of the rainwater runoff shall be calculated in accordance with the Building Code for sewerage structures or, depending on the average rainfall intensity and runoff formation conditions, by using the simplified method:

Q_max = ψ × F × q × 10^-3, where (27):

Q_max - estimated flow rate (m³/s);

Ψ - runoff coefficient (ψ = 0.95 for asphalt concrete and concrete surfaces; ψ = 0.45 for paving; ψ = 0.30 for compacted gravel surfaces; ψ = 0.20 for ordinary soil areas; ψ = 0.10 for lawns).

F - runoff catchment area (ha), for each type of surface separately;

q = 0.13 × α - runoff modulus (l/s·ha) with a recurrence probability of 2 times per year;

α - average rainfall intensity coefficient (Table 1 of Annex 2 to this Building Code).

181. Incoming surface waters shall be intercepted by contour ditches or chutes which are designed along the upper contour of the area to be drained and discharged into a water drain, water body, or surface water sewer system. The parameters of contour ditches shall be adopted according to the parameters of the boundary grid of agricultural land drainage systems.

182. To promote and organise surface runoff from built-up areas, roads, streets, and squares, the areas shall be graded to provide a slope of at least 3 to 6 ‰ towards street and road chutes and stormwater collection wells.

183. For the interception of the surface runoff from low-rise built-up areas and parks and its conveyance to sewerage treatment facilities, it shall be permissible to use storm drain ditches, road ditches or chutes.

184. If the groundwater level is elevated in a low-rise built-up area, in conformity with the territorial plan, surface drainage trenches or drains shall be designed along the plot boundaries, and also foundation or ring drainage for buildings. The runoff from drainage systems shall be discharged by gravity or pumping into storm drain ditches, road ditches or chutes, and also into a water drain or water body.

185. The parameters of surface drainage trenches shall be determined by the relief and soil conditions of the area, but shall be limited by the depth of the water drain or surface water sewer system and the possibilities for ditch placement in the built-up area. The bottom width of surface drainage trenches shall be assumed as 0.4 m, and the slope gradient coefficient from 1 to 1.5. If it is necessary to reduce the area occupied by ditches, steeper slopes may be designed and reinforced. The permissible minimum longitudinal gradient of the bottom of surface drainage trenches shall be 0.5 ‰.

186. For the interception of the surface runoff from built-up areas and its conveyance to sewerage treatment facilities, storm drain engineering structures may be used.

187. If the groundwater level is elevated in a built-up area, continuous drainage of the territory, foundation or ring drainage for buildings shall be designed. The drain runoff shall be discharged by gravity or pumping into the storm drain system wells and into a water drain or water body.

188. The drain spacing for continuous drainage of the territory shall be determined in accordance with the territorial plan, depending on the required lowering of the groundwater level, the layout of structures, and the possible construction depth of the drain pipe. The diameter of the drainage pipes shall be at least 75 or 100 mm, and the minimum longitudinal gradient at least 0.3 %.

189. If the main cause of overwetting in the built-up area is pressurised water saturating the low-permeability soil layer at the level of the building foundations, foundation drainage shall be used. Beneath the building, up to the collecting drain and along the external walls, a base of gravel or coarse sand with a thickness of 0.2 to 0.3 m shall be constructed, and drain pipes shall be installed in the vicinity of the building walls.

190. For the protection of individual buildings or groups of buildings against elevated groundwater level, ring drainage shall be used which surrounds the protected object on all sides or only on the side with the greatest inflow. The drain pipe shall be constructed along the external contour of the building at least 0.3 m below the footing level of the building foundation and shall be covered with a gravel layer at least 0.3 m in thickness. If the groundwater inflow is particularly pronounced, drains may also be installed beneath the basement floor of the building at intervals of 4 to 8 m and at least 0.5 m below the basement floor level.

191. For foundation and ring drainage of buildings, clay or plastic drain pipes, and also perforated pipes made of other materials with a minimum diameter of at least 100 mm may be used. The minimum longitudinal slope of the drain pipe shall be 0.3 %.

192. The distances from the drains to the nearest structures shall be determined in accordance with the Building Code regarding the placement of utility networks, but not less than as specified in the legal acts.

193. At the downstream end of the drainage system bed, before entering the surface water sewer system, it shall be recommended to construct a sediment basin and, for the inlet opening to the sewer well (chamber), to install silt retention screen. The gaps between the screens shall not exceed 40 mm.

194. If the groundwater level in the territory of populated areas is too high and cannot be lowered by the previously specified measures or if it is otherwise not feasible, an area colmatage project may be designed - raising the land surface level of the territory by importing soil or by dredging using a hydromechanisation method. When carrying out colmatage, the collection and drainage of surface runoff from the colmataged area shall be ensured so that it does not flow onto the surrounding areas, and a free runoff path from the surrounding areas shall also be provided.

8. Hydrotechnical Structures

195. For the use of water resources, prevention of the harmful effects of waters, and also ensuring the operation of land amelioration systems, hydrotechnical structures shall be designed to perform the following functions:

195.1. regulation of runoff and water levels (water reservoirs, ponds, dams, drainage structures);

195.2. use of water resources (hydroelectric power plants, watermills, pumping stations);

195.3. connection of watercourse water levels (rapids, weirs);

195.4. protection of the surrounding territories against flooding and overwetting (protecting dikes);

195.5. conveyance of watercourses over various obstacles and terrain depressions (culverts, aqueducts);

195.6. strengthening the banks of watercourses and water bodies and regulation of streams (dams, groynes, breakwaters, bank reinforcements, embankments);

195.7. ensuring and protecting fish migration (fish passes, fish protection devices).

196. When designing hydrotechnical structures, various hydrotechnical structures may be combined into a single hydrotechnical node, and they may be used for different purposes (for example, land drainage, fisheries, water supply, recreation, hydropower engineering).

8.1. Basic Calculation Requirements

197. For the design of hydrotechnical structures, estimated flow rates with the exceedance probability specified in Annex 1 to this Building Code (%) shall be used.

198. Hydraulic calculations shall be used to determine the throughput capacity and other parameters of hydrotechnical structures.

199. The height of runoff and level regulation dams and the throughput capacity of drainage structures shall be calculated at two upper reach water levels, assuming the greater of the two:

199.1. at the normal impounding level during the discharge of the estimated flow rate with all drainage structure openings fully open;

199.2. at the highest impounding level during the discharge of the verification flow rate with all drainage structure openings fully open.

200. The design and verification of calculations for hydrotechnical structure constructions shall be carried out in accordance with the building codes for the design of concrete, steel, and masonry structures, and also in the field of geotechnics.

8.2. Regulation of the Runoff and Water Levels

201. Water retaining and drainage structures (for example, dams, regulators, spillways, outlets) shall allow to regulate runoff and water levels and to accumulate water in reservoirs or ponds.

202. Depending on the purpose of use of the water reservoir (pond), they shall be classified as agricultural, fishery, hydroelectric, water supply, recreational, and multipurpose water reservoirs (ponds).

203. Depending on the structural design, there may be watercourse or lake reservoirs, excavated ponds, or mixed-type water reservoirs (ponds).

8.2.1. Water Reservoirs

204. The construction intention documentation of the water reservoir shall specify:

204.1. the water reservoir at the normal water impounding level which is the highest permissible water level in the water reservoir that is ensured by the hydrotechnical node (drainage structure) under normal operating conditions and occurs in the water reservoir when the estimated flow rate is discharged through fully opened drainage structure openings or over the spillway crest. At the normal water impounding level, the surface area, total volume, and other parameters characterising the water reservoir shall be determined;

204.2. the water reservoir at the highest impounding level which is temporarily permissible in the water reservoir during spring flood periods and which occurs when the test flow rate is discharged through fully opened drainage structure openings;

204.3. the lowest impounding level of the water reservoir which is the lowest water level in the reservoir and up to which, under normal operating conditions of the hydrotechnical node (drainage structure), the lowering of the water reservoir level (lowering of the normal water impounding level) is permissible;

204.4. the useful volume of the water reservoir which is the part of its total volume between the normal and the lowest water impounding level that is used for regulating runoff to ensure the required water consumption and regulated flow rate in the lower reach.

205. In the water reservoir, permanent and temporary flooding, overwetted, and shallow water zones form:

205.1. a permanent flooding zone forms in the water reservoir from the bed up to the normal water impounding level, the development of agricultural crops and trees, and also other economic activities is not possible therein, except for fishery and recreation;

205.2. a temporary flooding zone forms during floods between the normal and highest water impounding level, and the evolution of grasslands and certain tree species is possible therein;

205.3. an overwetted zone forms in the area adjacent to the water reservoir, and the groundwater level is elevated therein as a result of water impounding. The impact of overwetting shall be predicted depending on hydrogeological conditions but, as a guideline, it may be 1.5 to 2 m above the normal water impounding level;

205.4. a shallow water zone shall be considered the area of the water reservoir where the water depth at the normal water impounding level is less than 0.5 m.

206. Hydrological and water management calculations shall be used to determine the required useful volume of the water reservoir which, taking into account possible evaporation from the water surface and filtration losses, the required flow rate to be maintained in the watercourse, and other economic and environmental protection requirements, ensures the necessary water consumption and planned usage possibilities.

207. The main criterion which is required for the preservation of the natural biological resources and ecosystems of the watercourse and by which the water management balance is assessed is the flow rate to be maintained in the watercourse (in the lower reach of the drainage structure). In order to preserve the natural state of the watercourse downstream of the water reservoir as much as possible during low-water periods, if permitted by the volume of natural inflow, evaporation, and the lowest water impounding level in the water reservoir, the construction intention documentation shall specify and ensure, by technical means, a permanent watercourse:

207.1. the minimum guaranteed flow rate which is accepted as the minimum flow rate for a 30-day summer period with 95 % assurance;

207.2. in watercourses of particular importance for fisheries, based on the opinion of the fishery expert assessment on the impact of the operation on fish resources, the regional environmental authority may, when issuing technical design requirements, set an increased ecological flow rate (up to the minimum 30-day summer flow rate with 50 % assurance);

207.3. in order to ensure the preservation and protection of the natural biological resources and ecosystems of the watercourse, the regional environmental authority may, based on the opinion of an environmental expert registered in accordance with the procedures specified in the laws and regulations regarding the impact of the operation on the state of the environment, set an ecological flow rate.

208. The construction intention documentation of the water reservoir shall forecast the impact of the water reservoir on the groundwater regime, bank stability, and shoreline transformation. If necessary, protective measures shall be designed - grading and reinforcement of bank slopes, construction of drainage and other anti-filtration structures.

209. Prior to water level impoundment, the bed shall be prepared in which the following shall be carried out:

209.1. felling of vegetation (trees and shrubs), removal and extraction of stumps from the permanent flooding zone;

209.2. felling and removal of vegetation in the temporary inundation zone that does not tolerate temporary flooding;

209.3. removal and extraction of peat with the potential for floating from the permanent flooding zone or weighting it down with a soil embedment;

209.4. deepening of potential shallow water zones;

209.5. sealing of boreholes and artesian wells.

8.2.2. Excavated Ponds

210. Under favourable hydrogeological conditions, surface runoff and groundwater inflow may be accumulated in excavated (partially cut-and-fill) ponds.

211. If the inflow to the excavated pond is provided by groundwater or the inflow of surface waters is insignificant in the water balance of the pond, the average, highest, and lowest water levels of the pond shall be forecast depending on the pond bed soil conditions, the natural groundwater level, planned consumption, and evaporation from the pond water surface.

212. The slopes of an excavated pond shall be designed in accordance with the requirements for the slopes of diverting ditches and water drain slopes or shall be flatter.

213. If a pond is constructed in permeable soil and the average water level in the pond is expected to be higher than the natural groundwater level or if filtration through the bed or slopes of the excavated pond exceeds the permissible limit, anti-filtration protection of the pond bed and slopes shall be designed, using artificial colmatage, clay, peat (with a degree of decomposition of 50 % or more), plastic film, and other low-permeability materials.

8.2.3. Dams

214. Soil dams for water level impoundment shall be designed as non-overflow structures; however, for the drainage and regulation of water inflow, a drainage structure shall be constructed within the body of the dam. Concrete (reinforced concrete) dams shall simultaneously serve for water level impoundment and for the conveyance of water into the lower reach.

215. The type of embankment soil dam, depending on the properties of the foundation soil and the depth of the impermeable soil layer beneath the dam, may be determined in accordance with Table 2 of Annex 13 to this Building Code.

216. Any soil may be used for the construction of a soil dam, except for soil in which:

216.1. the admixture of water-soluble chloride salts is greater than 5 % or the content of sulphate-chloride salts is greater than 10 % of the mass of the embanked soil;

216.2. the content of partially decomposed organic matter, e.g. plant or tree residues, is more than 5 % or the amorphous mass of fully decomposed organic matter is more than 8 % of the mass of the embanked soil.

217. The optimal soil for the construction (embankment) of the body of an earth dam shall be loam and loamy sand. When using clay, it shall be protected against frost penetration by an embedment layer of sand, loamy sand, or gravel. The body of a sand dam shall be provided with anti-filtration structures.

218. For the construction of a soil dam (dredging) using hydromechanisation methods, sand soil shall be the most suitable, whereas clay soil shall not be suitable for the dredging of homogeneous dams.

219. The most suitable soil for anti-filtration in a soil dam shall be clayey soil with a filtration coefficient less than 0.1 m/d and a plasticity index greater than 0.05. For the screen and the upstream blanket, peat covered with mineral soil may be used, with its degree of decomposition is 50 % or greater.

220. The elevation of the dam crest shall be determined, taking into account wind-induced surge, wave run-up, and height allowance at two water levels in the upper reach:

220.1. the normal water impounding level when wind-induced surge and wave run-up are calculated at the maximum wind with a 4 % exceedance probability;

220.2. the highest water impounding level when wind-induced surge and wave run-up at maximum wind are calculated with a 50 % exceedance probability;

220.3. in both calculation cases, the height allowance is 0.5 m.

221. If a road or railway is planned over the dam, the elevation of the roadbed surface above the highest water level in the upper reach shall be determined by the laws and regulations governing road or railway construction.

222. The minimum width of the dam crest shall be 4.5 m. If a road or railway is planned over the dam, the width of the dam crest shall be determined by the laws and regulations governing road or railway construction.

223. The gradient of the dam slopes shall ensure slope stability which depends on the mechanical properties of the dam body and foundation soil, and also on the forces impacting the slope and the height of the dam, and this shall be verified by a dam stability calculation for cylindrical slip surfaces.

224. The dam slopes shall be protected against the effects of waves, ice, water flow, atmospheric precipitation, and other harmful factors.

225. The filtration stability of the dam body and anti-filtration devices shall be calculated at the highest water pressure (highest water impounding level). In general case, the actual average pressure gradient J_est (m) shall be equal to or less than the calculated (with safety factor γ_n) average critical gradients indicated in Table 1 of Annex 13 to this Building Code.

226. In order to reduce filtration flow through the dam body or foundation and to increase the stability of the lower reach slope of the dam, anti-filtration structures made of low-permeability material - such as a dam screen, upstream blanket, diaphragm, core, or pile planking - shall be designed, taking into account the following:

226.1. the minimum thickness of the screen and the minimum width of the top of the core shall be 0.8 m;

226.2. the elevation of the screen surface shall be higher than the highest water impounding level, including wind-induced surge and wave run-up height;

226.3. the elevation of the core surface shall be higher than the highest water impounding level, including wind-induced surge;

226.4. the minimum thickness of the upstream blanket shall be 0.5 m.

227. In order to prevent the outlet of filtration flow in the frost penetration zone of the lower reach slope of the dam, to lower the position of the filtration depression curve, and to divert the filtration flow into the lower reach without slope deformations, the drainage of the dam shall be designed as follows:

227.1. if the lower reach slope of the dam is not permanently flooded, pipe drainage with a filter material embedment may be used. The minimum diameter of the drainage pipes shall be 200 mm;

227.2. if uneven settlement of the dam foundation is possible or the lower reach slope of the dam is permanently flooded, a stone drainage prism or backfill may be used. The surface of the drainage prism shall be at least 0.5 m above the highest water level in the lower reach.

228. Between the drainage prism or backfill, core, screen, and the dam body, including a fine sand base, an inverted filter shall be constructed as follows in order to prevent clogging of the drainage by fine soil particles and the occurrence of suffosion in the dam body:

228.1. the minimum thickness of each layer of the inverted filter shall be 0.2 m;

228.2. the average size of the fractions of the individual layers of the inverted filter, drainage, and transition shall gradually increase in the direction of the filtration flow, and their non-uniformity coefficient k_{60, 10} (the ratio of the average size of the ground fraction the mass of which together with finer fractions is 60 % of the total mass to the fraction the average size of which is 10 % of the total mass) depending on the protected ground material shall be less than or equal to:

228.2.1. 15 - for fine sand;

228.2.2. 20 - for sand and gravel;

228.2.3. 25 - for broken stone;

228.2.4. 50 - for clay soils.

229. In order to prevent dangerous filtration along the contact surface between the dam body and the foundation:

229.1. the topsoil shall be removed from the dam foundation, tree and shrub roots or the soil layer occupied by them shall be excavated, as well as the soils specified in Paragraph 216 of this Building Code shall be removed. A low-permeability soil tooth, diaphragm, or pile planking shall be constructed in the dam foundation;

229.2. if the dam is constructed on a rocky foundation with a weathered surface layer, the weathered layer shall be removed, and low-permeability soil teeth, diaphragm or foundation cementation or clay injections shall be used in the dam foundation.

8.2.4. Drainage Structures

230. Drainage structures (regulators, spillways, and outlets) shall be designed for the discharge of inflows which cannot be accumulated in the water reservoir (pond) for conveyance to the lower reach, to regulate water levels in the water reservoir and lower reach, or to empty the water reservoir.

231. For the drainage of spring flood and flood waters, it shall be advisable to design automatically operating drainage structures - spillways which are usually of the shaft type or have a wide practical profile.

232. The parameters of the drainage structures shall be determined by the conditions for the discharge of the estimated and check flow rates specified in Paragraphs 197 and 199 of this Building Code.

233. The drainage structure shall ensure the possibility to lower the water level in the upper reach to a level required for the inspection and repair of other structures of the hydrotechnical node.

234. The design of the drainage structure shall ensure the dissipation of the energy of the conveyed water in order to prevent a dam washout.

235. Assessing the rate of rise of spring and other flood and high water levels, ice, frazil ice, and floating debris conditions and the requirements for ecological flow rate conveyance, a scheme for the operation of discharge gates of the drainage structure shall be developed in the construction intention documentation.

236. Upstream of the working discharge gates on the upper reach side and, if the lower reach may be flooded, also in the outlet section of the lower reach, provision shall be made for the possibility of inserting repair-emergency gates (stop planks).

8.3. Use of Water Resources

237. Water intake structures and supply structures shall ensure unobstructed intake of the required amount of water from the water source and its conveyance to the hydromechanical equipment, as well as the possibility to isolate equipment for inspection, repair, and in case of emergency:

237.1. in order to prevent floating debris, ice, and frazil ice from entering the hydromechanical equipment, protective screens, water settling devices, and other protective devices shall be designed;

237.2. in order to prevent fish and juvenile fish from entering the hydromechanical equipment, fish protection devices shall be designed (Sub-section 8.4.1 of the Building Code);

237.3. repair-emergency gates (stop planks) may be installed in water intake structures;

237.4. if water supply pipes are installed above ground, protection against deformations caused by temperature differences and uneven settlement shall be provided. If steel and reinforced concrete pipes are used, corrosion protection shall be provided.

238. For the retention of floating debris and refuse, a screen shall be installed perpendicularly to the water flow at an inclination of 70° to 80° or vertically:

238.1. for submerged pumps in pumping stations, grates may be designed around the perimeter (360° or less);

238.2. the width of the grate openings in pumping stations shall be consistent with the width of the pump impeller channel. The width of the openings shall be designed as 20 mm for centrifugal pumps and 35 mm for propeller pumps;

238.3. in order to reduce the possibility of fish and juvenile fish entering hydro units through the protective screen of hydroelectric power plants and watermills, the distance between the bars of the protective grates shall not be greater than 35 mm;

238.4. the water flow speed at the grates shall not exceed 0.6 m/s.

239. The structure of pumping stations, hydroelectric power plants, or watermill buildings shall be determined by the type, number, and capacity of the equipment to be installed.

240. Pumping equipment shall be designed so that the pumps operate without cavitation and ensure the required capacity, pumping head and pressure in all operating modes.

241. Turbine units in hydroelectric power plants and watermills shall ensure cavitation-free operation in all operating modes.

242. In drainage pumping stations, each pump shall be designed with its own inlet or suction pipe, with the suction pipe sloping towards the pump at a gradient of at least 0.005.

243. The number of pressure pipes in drainage pumping stations shall be designed in equal number to pumps. For release into the water drain, a smooth connection of the water flow with the water drain shall be ensured:

243.1. the mark on the top surface of the pressure pipe outlet during the winter minimum water level shall be at least 0.2 m below the underside of the ice cover;

243.2. the outlet shall be equipped with mechanical closing devices or a siphon to prevent backflow of water when the pump is not operating;

243.3. the lowest point of the siphon pipe at the highest point of the siphon shall be at least 0.2 m higher than the highest calculated water level in the water drain, including wind-induced surges and wave run-up height;

243.4. if mechanical closing devices are used for water release, repair-emergency gates (stop planks) shall be provided in the water discharge assembly for inspection and repair of the closing devices.

244. Pumping stations requiring water resources use permits shall be provided, in the construction intention documentation, with measuring equipment for recording the quantity of water pumped.

245. The operation of drainage pumping stations shall be automated, with pumps switching on and off depending on the specified water levels in the storage basin.

246. The inlets to the turbine chambers of hydroelectric power plants and watermills shall be closed with adjustable gates, and repair-emergency gates (stop planks) shall be provided in the turbine inlet channel and lower reach for the repair of turbines and discharge gates.

247. For the operation of technological equipment, fittings, and pipelines of pumping stations, hydroelectric power plants, and watermills, it shall be recommended to use the following lifting devices:

247.1. if the load mass does not exceed 1 tonne - fixed single-rail tracks with hoists and travelling trolleys, hoists, and manually operated beam cranes;

247.2. if the load mass is 1 to 5 tonnes - beam cranes;

247.3. if the load mass exceeds 5 tonnes - bridge cranes;

247.4. if the load must be lifted higher than 6 m and moved further than 18 m, only electrified lifting and transport devices shall be used.

8.4. Fish Protection and Migration Structures

248. Hydroelectric power plants, watermills, and other water intake structures in watercourses and water bodies shall be designed with fish protection structures.

249. In case of the construction of hydroelectric power plants and other dams on watercourses and water bodies of significant fisheries importance, fish migration structures shall also be designed.

8.4.1. Fish Protection Devices

250. Fish protection devices shall be a component of water intake structures, and the ichthyological characteristics of the watercourse or water body shall be assessed when designing intake facilities. Intake facilities shall not be designed in pronounced fish spawning, wintering, and concentration areas.

251. The design of fish protection structures shall be determined by the flow and stream velocities in the water source and intake facility in order to ensure the retention or removal of fish and juvenile fish from the protected area, preventing their injury and loss of orientation.

252. The water intake structures of irrigation and summer polder pumping stations shall be designed with fish retention screens, diaphragms, or other structures, taking into account that:

252.1. if a fish barrier net is installed behind the debris retention grates, the mesh size, depending on the body length of the protected juvenile fish, may be accepted in accordance with Table 1 of Annex 14 to this Building Code;

252.2. if the water flow speed in the watercourse at the water intake location is at least three times greater than the inflow velocity in the intake facility openings, special fish protection devices in addition to the debris retention grates need not be designed.

253. The design widths of grate openings for debris retention grates at pumping stations, hydroelectric power stations, or watermills are determined in Sub-paragraphs 238.2 and 238.3 of this Building Code but, in order to reduce the entry of fish into hydromechanical equipment, the stream velocity before the screen and at the fish barrier nets of the intake facilities shall be designed to be less than one and a half times the removal speed of juvenile fish (Paragraph 256 of this Building Code).

8.4.2. Fish Migration Structures

254. If necessary, taking into account the distribution and number of fish species present in the watercourse, as well as the natural reproduction conditions upstream of the designed structure, or as concluded in the fisheries expert opinion, fish migration structures shall be designed.

255. Fish migration structures shall be designed for the estimated flow rate and water levels with a 5 % exceedance probability.

256. The characteristic stream velocities to be complied with in the selection of elements for fish migration structures and protection structures are specified in Table 2 of Annex 14 to this Building Code.

257. The type of a fish migration structure shall be determined according to the fisheries expert opinion. Fish ladders shall be mainly used to allow the migration of Salmoniformes from the lower reach to the upper reach.

258. In a fish migration structure, the entrance in the lower reach shall be at such a distance from the drop zone of the drainage structure that the stream velocity does not exceed the fish attraction speed and the attraction current from the fish migration structure reaches the fish concentration area.

259. The minimum width of the fish passage channel shall be 1.5 m, and the minimum water depth therein shall be 1 m.

260. The exit size of the fish migration structure in the upper reach and the distance to the discharge gate, spillway zone, or water intake structure of the drainage structure shall be such that the stream velocity in the exit zone does not exceed 0.4 m/s and the depth is greater than 2 m.

9. Environmental Protection Requirements

261. The construction intention documentation of land amelioration systems and hydrotechnical structures shall forecast the possible environmental changes. If negative environmental impact cannot be avoided, action shall be taken to ensure that such impact is minimal or mitigation measures, including compensation for damage caused to biocenoses, shall be included in the construction intention documentation.

262. In the construction intention documentation of land amelioration systems and hydrotechnical structures, the characteristic agrarian landscape shall be assessed from the aesthetic, historical, cultural, and ecological perspectives, it shall be improved and adapted to the requirements for nature protection and agricultural production. Undisturbed outcrops, caves, prominent boulders, heritage trees, characteristic landforms, springs, pronounced erosion gullies, and similar characteristic natural elements shall be preserved.

263. When designing land amelioration systems for agricultural land:

263.1. fields of optimal size (10 to 30 ha) and configuration (with a side ratio of 1:3 to 1:5) shall be created;

263.2. existing and newly created biocenoses, i. e., forest stands, watercourses, water bodies, natural meadows, untilled slopes, shall be used as contour elements;

263.3. local ravines and pronounced landform depressions shall be left undisturbed for the habitats of small animals and birds;

263.4. groups and rows of trees which may serve as windbreaks against wind erosion and, on steep slopes and banks, against water erosion shall be preserved;

263.5. when constructing contour ditches along the edge of the forest, care shall be taken not to disturb the trees growing along the forest edge, especially in the direction of prevailing winds in spruce stands which protect the forest from windthrow;

263.6. negative landscape elements shall be removed: building ruins, low-value shrubs, piles of stumps and stones.

264. When designing the route, longitudinal slope, and cross-section of a regulated or reconstructed water drain, if the necessary bed hydraulic conditions can be ensured and it is allowed by the soil properties, the following shall be complied with:

264.1. regulated sections of the watercourse shall be alternated with sections to be left in their natural state, including thresholds with reinforced bed sections under bridges, culverts, and bedrock elevations;

264.2. visually distinctive bed sections shall be preserved;

264.3. the natural route of the bed shall be followed, avoiding the creation of straight sections;

264.4. in certain sections, the cross-section of the bed shall be increased so that silt shoals form in favourable places;

264.5. pools, pits, sedimentation basins, riffles, fish shelters, and spawning grounds shall be created;

264.6. deeper sections of the bed shall be alternated with shallower ones and wider sections with narrower ones;

264.7. large stones shall be left in the bed or stone piles shall be formed as riffles;

264.8. oxbow lakes shall be cleaned and connected to the main bed;

264.9. beds to be reconstructed shall be excavated from one bank in order to preserve the other bank and slope undisturbed;

264.10. in watercourses where periodically flooded silt streaks have formed in the bed, the dynamic axis of the stream shall be directed towards the erodible bank, maintaining and enhancing the minor meandering of the bed.

265. The low-fertility soil excavated from the beds of watercourses shall be levelled over the surrounding area, excluding forest land, in a layer not exceeding 0.2 m in thickness, and this strip shall be ploughed with a breaking plough or disked after the soil has been levelled. In sections where the excavated soil may remain in the spoil heap and is not levelled, the topsoil shall be removed from the width of the base of the spoil heap and preserved for later use.

266. The topsoil shall be removed from the routes of large-diameter collectors, protective embankments, and pressure pipelines, and also from the foundations of hydrotechnical structures and preserved for later use.

267. In the lower sections of collecting ditches of peat deposit drainage systems and diverting ditches and water drains flowing out of forest peatlands, and also in the diverting ditches and water drains of agricultural and forest land drainage systems in specially protected areas, before their discharge into specially protected water bodies, sedimentation basins - sedimentation (destruction) ponds - shall be constructed by widening and deepening the bed to promote the settling of peat fines and other suspended solids.

268. In forest land and peat deposit drainage areas, excavated or impounded water bodies shall be designed in suitable locations for the needs of fire-fighting and forest animals.

269. When raising the water level in the water reservoir, the possible erosion and stability of the banks shall be forecast, and the water reservoir bed shall be prepared - vegetation, stumps, and debris must be removed from the flooding zone. Where necessary, banks shall be reinforced and the area of shallow water zones (where the water depth at the normal water impounding level is less than 0.5 m) shall be reduced.

270. In the construction intention documentation of land drainage and water bodies, changes in the groundwater regime shall be forecast and their impact on water supply wells and boreholes, and also springs and ponds shall be assessed.

271. In order to mitigate the possible negative impact of land amelioration systems and hydrotechnical structures on fish, the following shall be complied with in the construction intention documentation:

271.1. ground excavation and dredging works in watercourses and water bodies shall be carried out outside the fish spawning period;

271.2. depending on the water management balance conditions of the water reservoir and the design of the drainage structures, if they are suitable for fish migration, the openings of drainage structures shall be opened during the spawning period of valuable fish species;

271.3. in rivers of valuable fish species, fish spawning grounds shall be restored and new ones shall be created in suitable locations;

271.4. the depth of summer polder storage basins during the winter period, excluding ice thickness, shall be greater than 1.0 m;

271.5. water intake structures shall not be constructed in areas of pronounced fish concentration, spawning, or their wintering sites;

271.6. water intake structures and summer polder pumping stations shall be equipped with fish protection screens or other protective devices to prevent juvenile fish from entering the pumps;

271.7. if the fishery assessment of a watercourse or water body indicates the presence of valuable migratory or semi-migratory fish species for which natural reproduction upstream of the water retaining structure is appropriate and necessary and the water level differences in reaches and the stream velocities are acceptable for the migration of these fish, fish migration structures (fish passes) shall be designed;

271.8. the optimal operating regime for hydroelectric power stations, pumping stations, and other hydrotechnical node structures shall be selected to ensure:

271.8.1. the operation of hydromechanical equipment during daylight hours;

271.8.2. the discharge of the specified flow rate (minimum guaranteed or ecological) into the lower reach;

271.8.3. slow, gradual, or minimally variable changes in water levels in the upper and lower reaches.

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 1
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Annual Exceedance Probability (%) of Estimated and Verification Hydrological Parameters

No.	Flow rates	Exceedance probability (%)	Structures to be designed, elements, calculation cases
1	2	3	4
1.	Maximum spring tide flow rate	0.1	Verification of the height of the runoff and water level regulation dams and the throughput capacity of drainage structures
2.	Maximum spring tide flow rate	1	1. Calculation of the height of runoff and water level regulation dams and the throughput capacity of drainage structures. 2. Calculation of the height of non-overtopping protective embankments. 3. Calculation of the throughput capacity of bridges and culverts on main AI category roads (streets). 4. Calculation of the throughput capacity of railway bridges and culverts of strategic and regional importance for public use
3.	Maximum spring tide flow rate	2	1. Calculation of the throughput capacity of bridges and culverts on regional AII and AIII category roads and BII category roads (streets) in cities and populated areas. 2. Calculation of the throughput capacity of railway bridges and culverts intended for private use
4.	Maximum spring tide flow rate	3	Calculation of the throughput capacity of bridges and culverts on rural AIV category roads
5.	Maximum spring tide flow rate	5	1. Calculation of the throughput capacity and height of water level connection structures. 2. Calculation of the reinforcement of water drains and diverting ditch beds and the slopes of protecting dikes. 3. Calculation of the throughput capacity and height of fish migration structures. 4. Calculation of the throughput capacity of bridges and culverts on rural AV and AVI category roads
6.	Maximum spring tide flow rate	10	Calculation of the throughput capacity of water drains and diverting ditch beds in inhabited areas and areas which are used as fields and pastures
7.	Maximum flow rate of summer-autumn floods	2	Verification of the throughput capacity of water drains and diverting ditch beds in inhabited areas and areas which are used as fields and pastures
8.	Maximum flow rate of summer-autumn floods	5	Calculation of the height of summer polder protecting dikes if the polder areas are used for the cultivation of spring crops, vegetables, technical crops or forage crops
9.	Maximum flow rate of summer-autumn floods	10	1. Calculation of the throughput capacity of water drains and diverting ditch beds in areas which are used for meadows and forests. 2. Calculation of the height of summer polder protecting dikes if the polder areas are used for meadows and pastures
10.	Summer half-year flow rate	50 (average)	Determination of drain outlet elevation marks
11.	Maximum daily precipitation intensity	10	Calculation of surface runoff inflow for drainage

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 2
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Calculation of the Maximum Flow Rate of Spring Tide

Map 1

Maximum Flow Rate Steepness Coefficient of Spring Tide, k₁ (%)

Map 2

Spring Tide Runoff Layer, p = 1 % (mm)

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 3
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Maximum Runoff Module of Summer-Autumn Flood, q₂₀₀ (m³/s x km²)

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 4
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Long-term Annual Average Runoff Layer (mm)

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 5
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Average Runoff Module of Summer Half-year (l/s x km²)

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 6
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Calculation of Minimum Runoff

Map 1

Geomorphological Regions with Minimum Runoff

Map 2

Climatic Parameter (g) for the Formation of a Minimum Runoff in the Winter Half-year

Map 3

Climatic Parameter (g) for the Formation of a Minimum Runoff in the Summer Half-year

Table 1

Parameters a₁, a₂, a₃, a₄, b Depending on the Exceedance Probability of the Minimum Flow Rate (%)

No.	Exceedance probability of the minimum flow rate (%)	Characteristics
		a1	a2	a3	a4	b
1	2	3	4	5	6	7
1.	Minimum 30-day summer flow rate:
	p = 75 %	0	0.0021	0.0042	0.017	7.6
	p = 85 %	0	0.0016	0.0035	0.014	7.6
	p = 95 %	0	0.0013	0.0028	0.011	7.6
2.	Minimum 30-day winter flow rate:
	p = 75 %	0	0.0056	0.0085	0.017	9.0
	p = 85 %	0	0.0036	0.0060	0.015	9.0
	p = 95 %	0	0.0023	0.0045	0.0015	9.0

Notes.

1. For catchment areas with an area greater than 5000 km², long-term hydrometric observation data shall be used, but for catchment areas with an area less than 20 km², the hydrological regime shall additionally be assessed with at least 3-4 flow rate measurements in the field.

2. For additional information which may be obtained from the maps provided in annexes, all known data on the conditions of the specific catchment area shall be used. This is particularly relevant for separation of the marginal zone R₄ which can only be carried out safely by taking into account the local hydrogeological conditions.

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 7
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Permissible Maximum Stream Velocity

Table 1

Permissible Maximum Stream Velocity v₀ (m/s) in Unreinforced Beds

No.	Soil	Soil characteristics (mm), (kg/cm2), (%)	Water depth (m)
			0.25	0.50	1.0	1.5	2.0	2.5	3.0	3.5
1	2	3	4	5	6	7	8	9	10	11
I. Sand Soils (with Average Soil Particle Size (mm))
1.	Fine sand	0.05-0.25	0.30-0.35	0.30-0.35	0.35-0.40	0.35-0.40	0.40-0.45	0.40-0.45	0.40-0.45	0.40-0.45
2.	Medium coarse sand	0.25-1.0	0.35-0.40	0.35-0.50	0.40-0.55	0.40-0.60	0.45-0.60	0.45-0.60	0.45-0.65	0.45-0.65
3.	Coarse sand	1.0-3.0	0.45-0.65	0.50-0.70	0.55-0.75	0.60-0.80	0.60-0.80	0.60-0.85	0.65-0.85	0.65-0.85
4.	Fine gravel	3.0-5.0	0.65-0.80	0.70-0.85	0.75-0.95	0.80-1.00	0.80-1.05	0.85-1.05	0.85-1.15	0.85-1.10
5.	Coarse gravel	5.0-10.0	0.80-1.05	0.85-1.15	0.95-1.25	1.00-1.30	1.05-1.35	1.05-1.40	1.10-1.45	1.10-1.45
II. Cobbles, Stones, and Rock Soils (with Average Particle Size (mm) or Soil Resistance (kg/cm2))
6.	Cobbles	10-20	1.05-1.30	1.15-1.45	1.25-1.55	1.30-1.60	1.35-1.70	1.40-1.75	1.40-1.80	1.45-1.80
7.	Cobbles	20-30	1.30-1.50	1.45-1.60	1.55-1.75	1.65-1.85	1.70-1.90	1.75-1.95	1.80-2.00	1.80-2.05
8.	Stones	30-75	1.50-2.00	2.60-2.15	1.75-2.35	1.85-2.45	1.90-2.55	1.95-2.60	2.00-2.70	2.05-2.75
9.	Stones	75-150	2.00-2.40	2.15-2.60	2.35-2.85	2.40-3.00	2.55-3.10	2.60-3.20	2.70-3.25	2.75-3.30
10.	Stones	150-300	2.40-2.80	2.60-3.05	2.85-3.30	3.00-3.45	3.10-3.60	3.20-3.70	3.25-3.75	3.30-3.80
11.	Laminated limestone, fissured dolomite	-	1.7-2.5	1.8-2.8	2.0-3.0	2.1-3.2	2.2-3.3	2.2-3.3	2.3-3.4	2.3-3.5
12.	Monolithic limestone, dolomite	100-200 kg/cm2	2.5-4.2	2.8-4.6	3.0-5.0	3.2-5.2	3.3-5.4	3.3-5.6	3.4-5.7	3.5-5.8
13.	Monolithic limestone, dolomite	500-1000 kg/cm2	6.0-8.5	6.4-9.2	7.0-10.0	7.4-10.5	7.8-10.9	7.8-11.1	8.0-11.4	8.1-11.6
III. Clay Soils (with Content of Clay Particles Smaller than 0.01 mm (%))
14.	Cohesive sand	5-10	0.40-0.45	0.45-0.50	0.50-0.55	0.50-0.60	0.55-0.60	0.55-0.60	0.60-0.65	0.60-0.65
15.	Clayey sand	10-20	0.45-0.65	0.50-0.70	0.55-0.75	0.60-0.80	0.60-0.80	0.60-0.85	0.65-0.85	0.65-0.85
16.	Light loam	20-30	0.65-0.80	0.70-0.85	0.75-0.95	0.80-1.00	0.80-1.05	0.85-1.05	0.85-1.10	0.85-1.10
17.	Medium loam	30-40	0.80-0.90	0.85-0.95	0.95-1.05	1.00-1.10	1.05-1.15	1.05-1.15	1.10-1.20	1.10-1.20
18.	Heavy loam	40-50	0.90-1.00	0.95-1.10	1.05-1.20	1.10-1.25	1.15-1.30	1.15-1.35	1.20-1.35	1.30-1.40
19.	Light clay	50-60	1.00-1.10	1.10-1.20	1.20-1.30	1.25-1.35	1.30-1.40	1.35-1.45	1.35-1.50	1.40-1.50
20.	Medium clay	60-80	1.10-1.20	1.20-1.30	1.30-1.40	1.35-1.45	1.40-1.50	1.45-1.55	1.50-1.60	1.50-1.65
21.	Heavy clay	More than 80	1.20-1.25	1.30-1.35	1.40-1.45	1.45-1.50	1.50-1.60	1.55-1.60	1.60-1.65	1.65-1.70
22.	Marly clay (with CaCO3 content 5-20 %)	-	1.35-1.50	1.45-1.65	1.60-1.80	1.70-1.90	1.75-1.95	1.80-2.00	1.85-2.05	1.85-2.10
IV. Peat Soils (with Degree of Peat Decomposition (%))
23.	Wood peat	-	0.70	0.75	0.80	0.85	0.85	0.90	0.90	0.95
24.	Well-decomposed herbaceous peat	More than 50 %	0.50	0.55	0.60	0.65	0.65	0.65	0.70	0.70
25.	Poorly decomposed herbaceous peat	Less than 35 %	0.75	0.85	0.90	0.95	1.00	1.00	1.00	1.05
26.	Well-decomposed sphagnum peat	More than 50 %	0.60	0.65	0.70	0.75	0.75	0.80	0.80	0.80
27.	Poorly decomposed sphagnum peat	Less than 35 %	1.00	1.10	1.20	1.25	1.30	1.35	1.35	1.40

Table 2

Permissible Maximum Stream Velocity v₀ (m/s) in Reinforced Channels

No.	Type of reinforcement	Water depth (m)
		0.25	0.50	1.00	1.50	2.00	2.50	3.00	3.50
1	2	3	4	5	6	7	8	9	10
1.	Continuous turfing	1.05	1.15	1.25	1.30	1.35	1.40	1.45	1.50
2.	Turf wall	1.40	1.55	1.70	1.80	1.85	1.90	1.95	2.00
3.	Stone paving with stone size 12-20 cm	2.35	2.55	2.80	2.95	3.05	3.15	3.25	3.30
4.	Stone paving with stone size 20-30 cm	2.75	3.00	3.30	3.50	3.60	3.70	3.80	3.90
5.	Stone mound (diameter 10-15 cm) in wattle mesh; concrete slabs	2.90	3.20	3.50	3.70	3.80	3.95	4.05	4.10
6.	Stone paving in cement mortar with stone size 20-30 cm	4.20	4.55	5.00	5.25	5.45	5.65	5.75	5.90
7.	Wooden chutes	6.70	7.30	8.00	8.45	8.75	9.00	9.25	9.40
8.	Concrete bed, concrete class B7.5	11.5	12.6	13.8	14.6	15.1	15.6	15.9	16.2
9.	Concrete bed, concrete class B22.5	17.7	19.4	21.2	22.4	23.2	23.9	24.4	25.0

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 8
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Calculation of Drain Spacing in Mineral Soils

Nomogram 1

Standard Drain Spacing E_n in Cohesive Soils

Nomogram 2

Standard Drain Spacing E_n in Non-cohesive Soils

Map 1

Moisture Coefficient

Table 1

Comprehensive Coefficient of Local Conditions, K_v

No.	Soil description	Land surface gradient up to 0.5 %		Land surface gradient 0.5-2.0 %		Land surface gradient 2.0-5.0 %		Land surface slope above 5.0 %
		Kv	Additional measures (note No.)	Kv	Additional measures (note No.)	Kv	Additional measures (note No.)	Kv	Additional measures (note No.)
1	2	3	4	5	6	7	8	9	10
I. Flat Areas, Upper Part of Slopes, and Slopes with a Uniform Gradient
1.	Gley mineral soils (g"')	0.9	1.	1.0	1.	1.0 (1.1)	-	1.1 (1.2)	-
2.	Gleyed mineral soils (g")	1.0	1.	1.1	1.	1.3 (1.4)	-	1.4 (1.7)	-
3.	Mineral soils with signs of gleying (g')	1.2	-	1.4	-	1.5 (1.8)	-	xx	-
4.	Loam and clay soils without signs of gleying	1.4	-	1.6	-	xx	-	xx	-
5.	Sand and loamy sand soils without signs of gleying	x	-	x	-	x	-	x	-
II. Intensely Wet Areas (Thalwegs, Saddle Points, Depressions, Pressure Water Discharge Sites, etc.)
6.	Gley mineral soils (g'")	0.7	2.	0.8	4.	0.9 (1.0)	4.	1.0 (1.2)	4.
7.	Gleyed mineral soils (g")	0.8	2.	0.9	4.	1.1 (1.2)	4.	1.2 (1.4)	4.
8.	Mineral soils with signs of gleying (g')	0.9	2.	1.0	4.	1.3 (1.4)	4.	1.4 (1.6)	4.
9.	Gley and gleyed humic mineral soils with mixed inflow	0.5 0.8	2. + 4 3.	0.5 0.8	2. + 4 3.	-	-	-	-
10.	Peat depressions	0.4 0.8	2. + 4 3.	0.4 0.8	2. + 4 3.	-	-	-	-

Notes.

1. ( ) - numbers in parentheses refer to slopes with southern exposure (S, SW, SE).

2. x - drainage is not designed (naturally dry).

3. xx - it is recommended to use local (selective) drainage.

4. No. 1 - subsoil filters shall be used.

5. No. 2 - depressions shall be opened, and surface water collectors together with subsoil filters shall be installed.

6. No. 3 - for additional drains, contour ditches or separate sections of diverting ditches shall be used.

7. No. 4 - the drain diameter shall be increased, and filter columns shall be used.

Table 2

Soil Chemical Properties Coefficient, K_k

No.	Chemical characteristics of soil and groundwater	Physical clay particle (< 0.01 mm) content (%)
		< 10	10-25	25-50	> 50
1	2	3	4	5	6
1.	Carbonate content up to the depth of 0.6 m (effervesces with 10 % hydrochloric acid)	1.00	1.00	1.05	1.10
2.	Iron compound content in groundwater (mg/l):
3.	< 3	1.00	1.00	1.00	1.00
4.	3-8	0.90	0.90	0.90	0.90

Table 3

Standard Drain Spacing E_n' Values in Bogs with a Poorly Filtering Base

No.	Peat layer thickness after initial settlement (m)	In bogs without wood and reed peat	In bogs with wood and reed peat
1	2	3	4
1.	0.6-0.9	12-14	14-16
2.	0.9-1.2	14-16	16-18
3.	1.2-1.5	16-18	18-20
4.	> 1.5	18-20	20-22

Table 4

Standard Drain Spacing E_n' Values in Bogs with a Well-filtering Mineral Base

No.	Peat layer thickness after initial settlement (m)	In bogs without wood and reed peat	In bogs with wood and reed peat
1	2	3	4
1.	0.6-1.5	26-30	28-32
2.	> 1.5	22-26	24-28

Table 5

Bog Hydrogeological Condition Coefficient K_h' values

No.	Characteristics of conditions	Kh'
1	2	3
1.	Atmospheric recharge	1.00
2.	Evenly distributed pressure water and inflow in inter-hill depressions	0.65-0.80

Table 6

Bog Hydrological Condition Coefficient K_a' values

No.	Characteristics of conditions	Ka'
1	2	3
1.	In places where drain outlets do not flood or their flooding during high water with a 10 % probability does not exceed 0.5 m	1.00
2.	In places where flooding of drain outlets during high water with a 10 % probability exceeds 0.5 m	0.85-0.90
3.	In flood-prone areas and summer polders	0.70-0.80

Table 7

Coefficient K of Iron Compound Content_k' Values

No.	Iron compound content in groundwater (mg/l)	Kk'
1	2	3
1.	< 3	1.00
2.	3-8	0.90

Table 8

Arrangement of Drainage System Elements Depending on the Spacing E_p of the Drainage Pipes

No.	Arrangement of drainage system elements	Design distances depending on the calculated spacing Ep of the drainage pipes
1	2	3
1.	Parallelly-arranged drainage pipes	Ep
2.	Drains placed laterally to each other	1/2 Ep
3.	Drains placed end-to-end	1 m, for contour drains - upstream ends connected
4.	Drains placed parallel to the diverting ditch	2/3 Ep, but not beyond the width of the levelled spoil heap, 1/4 Ep, if artesian water appears on the slope of the ditch, but not closer than 4 m
5.	Drains placed laterally to the diverting ditch	1/2 Ep, measured from the edge of the diverting ditch
6.	Drains placed parallel to the surface drainage trench, road ditch, or contour ditch	1/2 Ep, measured from the edge of the surface drainage trench or contour ditch, 1/4 Ep, measured from the edge of the road ditch
7.	Drains placed parallel to the field edge or boundary	1/3 Ep, measured from the field edge or boundary
8.	Drains placed laterally to the field edge, boundary, or road ditch	1 m
9.	Drains placed parallel to a collector with a pipe diameter greater than 175 mm	1/2 Ep

Table 9

Average Standards for the Drainage to be Designed (m)

No.	Land use	Drainage standard (optimal groundwater depth) (m)
		during the pre-sowing and harvest period	in the first month of the vegetation period	on average during the vegetation period
1	2	3	4	5
1.	Fields	0.4-0.6	-	0.9-1.1
2.	Pastures	-	0.7-0.9	0.9-1.1
3.	Meadows	-	0.4-0.6	0.6-0.8

Table 10

Average Installation Depth of Drains (m)

No.	Type of area use	Soil composition	Moisture coefficient Kū	Average installation depth of drains (m)
1	2	3	4	5
1.	Fields, pastures	Clay, loam		1.2-1.4
		Loamy sand, sand	< 1.0	1.1-1.3
		Loamy sand, sand	> 1.0	1.1-1.2
		Peat with a poorly filtering base		1.3-1.4
		Peat with a well-filtering base		1.1-1.2
2.	Meadows	Clay, loam	< 1.0	1.2-1.3
		Clay, loam, loamy sand, sand	> 1.0	1.1-1.2
		Peat with a poorly filtering base		1.1-1.3
		Peat with a well-filtering base		1.1
3.	Orchards, tree nurseries			1.4-1.6

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 9
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Calculation of Drain and Surface Runoff

Map 1

Drain Runoff Modules (l/s x ha) for Arable Land and Pastures

Map 2

Maximum Daily Precipitation Intensity (l/s x ha)

Table 1

Surface Runoff Modules (l/s x ha) in Arable Land

No.	Maximum daily precipitation intensity (l/s x ha)	Surface runoff module in drained areas (l/s x ha)
		sand	loamy sand, light and medium loam	heavy loam, clay
1	2	3	4	5
	I. Average Surface Gradient of the Land is Less than 0.5 %
1.	5.0	0.25	0.35	0.50
2.	5.5	0.30	0.40	0.55
3.	6.0	0.35	0.45	0.60
4.	6.5	0.40	0.55	0.70
	II. Average Surface Gradient of the Land is 0.51-3.0 %
5.	5.0	0.45	0.60	0.80
6.	5.5	0.50	0.65	0.90
7.	6.0	0.55	0.75	1.05
8.	6.5	0.60	0.85	1.20
	III. Average Surface Gradient of the Land is Greater than 3 %
9.	5.0	0.65	0.95	1.30
10.	5.5	0.70	1.05	1.45
11.	6.0	0.80	1.20	1.50
12.	6.5	0.90	1.35	1.90

Note. The average surface gradient of the land shall be determined as the arithmetic mean of the cross and longitudinal gradients of the catchment area.

Table 2

Minimum Longitudinal Gradient of Drainage Pipes and Collectors (%)

Nominal diameter of drains (mm)	50	75	100	125	150	175	200
Minimum longitudinal gradient (%)	0.30	0.30	0.20	0.20	0.20	0.20	0.20

Table 3

Main Parameters of Surface Drainage Trenches

No.	Soil description	Average for surface drainage trenches
		spacing (m)	depth (m)	slope gradient coefficient	penetration into mineral soil (m)
1	2	3	4	5	6
1.	Medium and well-permeable mineral soils (sand, loamy sand) with a filtration coefficient greater than 0.5 m/d	60-100	1.2-1.4	1.5-2.0	-
2.	Low-permeability mineral soils (clay, loam) with a filtration coefficient less than 0.5 m/d	40-60	1.0-1.2	1.5	-
3.	Peat above a medium to well-permeable base, with a peat depth of:
	up to 0.8 m	100-200	1.2-1.4	1.5	0.2-0.4
	0.8-1.3 m	100-180	1.3-1.5	1.5	0.2-0.4
	more than 1.3 m	100-160	1.5-1.8	1.25	0.2-0.4
4.	Peat above a low-permeability base, with a peat depth of:
	up to 0.8 m	60-80	1.1-1.2	1.5	0.1-0.3
	0.8-1.3 m	60-70	1.2-1.4	1.5	0.1-0.3
	more than 1.3 m	50-60	1.4-1.5	1.25	0.1-0.3

Table 4

Optimum Groundwater Level (m)

No.	Soil	Groundwater level (m)
		fields		pastures	meadows
		post-harvest period	in the later development phase
1	2	3	4	5	6
1.	Peat, light sand	0.4-0.5	0.8-0.9	0.7-0.8	0.6-0.7
2.	Sand	0.3-0.4	0.5-0.7	0.5-0.7	0.5-0.6

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 10
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Calculation of Irrigation Requirements

Map 1

Agroclimatic Regions of Latvia

Table 1

Average Daily Hydromodules (l/s x ha) and Average Irrigation Requirements for Agricultural Crops (m³/ha) (by Using Watering Method)

No.	Agroclimatic region (according to Map 1)	Average hydromodule (l/s x ha)	Average irrigation rate (m3/ha)
			irrigated crops
			early potatoes	tomatoes, table beetroot, carrots	cucumbers	early cabbage	mid-season and late-season cabbage	cultivated grasses
1	2	3	4	5	6	7	8	9
1.	Coastal Lowland:
	area adjacent to the Gulf of Riga	0.55	800-900	1000-1100	1100-1200	1200-1300	1500-1600	900-1600
	area adjacent to the Baltic Sea	0.50	650-700	800-900	900-950	950-1050	1200-1300	700-1300
2.	Kurzeme Upland	0.60	750-800	900-1000	1000-1100	1100-1200	1350-1450	800-1400
3.	Central Latvian Lowland	0.60	800-900	1000-1100	1100-1200	1200-1300	1500-1600	900-1600
4.	Vidzeme Upland	0.55	550-600	850-900	700-800	800-850	1050-1100	600-1100
5.	Lubāns Lowland	0.60	750-800	900-1000	1000-1100	1100-1200	1350-1450	800-1400
6.	Latgale Upland:
	south-western districts	0.65	800-900	1000-1100	1100-1200	1200-1300	1500-1600	900-1600
	other districts	0.60	750-800	900-1000	1000-1100	1100-1200	1350-1450	800-1400
7.	Northern Latvian Lowland	0.55	650-700	800-900	900-950	950-1050	1200-1300	700-1300

Note. The lower average irrigation rate shall be applied for irrigation on heavy soils, the higher rate for light sand and loamy sand soils, while the average irrigation rate shall be reduced by 15 % for cultivated grasslands on lowland bog peat soils.

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 11
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Table 1

Mutual Distances between Surface Drainage Trenches (m)

No.	Forest type	Forest stands		Distances between surface drainage trenches (m)
		site quality	forest stand type
1	2	3	4	5
1.	Callunoso-sphagnosa (Cs)	V	10P	150-240
2.	Vaccinioso-sphagnosa (Vs)	IV	10P	170-240
3.	Myrtilloso-sphagnosa (Ms)	III-IV	10P + E
	loamy sand soil			160-200
	loam soil			80-110
4.	Myrtilloso polytrichosa (Mp)	III-IV	10E + P	140-200
5.	Dryopteriosa (Dop)	III	10E, B, A, Os	150-190
6.	Sphagnosa (S)	V	10P	100-130
7.	Caricoso-phragmitosa (Cp)	IV-V	10P(B)	130-170
8.	Dryopteriosocaricosa (Do)	III-IV	10B (P,E)	180-240
9.	Filipendulosa (F)	I-II	10 M (Os, B)	180-240

Note. Smaller distances shall be designed in places where the inflow of pressure waters is possible and where there are strongly gleyed soils with a pronounced iron (ortstein) horizon. Larger distances shall be designed in water-permeable soils with a good land surface gradient (greater than 2 ‰) and higher forest stand quality.

Table 2

Average Depth of Surface Drainage Trenches (m)

No.	Soil profile		Depth of surface drainage trenches (m)
	layer thickness (m)	base mineral soil
1	2	3	4
1.	Humus, peat 0.2-0.5	sand, loamy sand	1.0-1.2
2.	Humus, peat 0.2-0.5	loam, clay	0.9-1.1
3.	Herbaceous peat 0.5-1.0	loamy sand, loam	1.2-1.3
4.	Herbaceous peat 1.0 and above	loam	1.3 or more
5.	Sphagnum peat 0.5-1.0	loam	1.3-1.4
6.	Sphagnum peat 1.0 and above	-	1.4 or more

Table 3

Surface Drainage Trench Slope Gradient Coefficient

No.	Ground characteristics	Slope gradient coefficient
1	2	3
1.	Sand, loamy sand	1.5
2.	Loam, clay	1.25
3.	Peat, well decomposed	1.25
4.	Peat, slightly decomposed	1.0

Table 4

Permissible Maximum Stream Velocities in Unreinforced Beds of Forest Land (m/s)

No.	Ground characteristics	Permissible maximum velocity (m/s)
1	2	3
1.	Sand, fine	0.4-0.6
2.	Sand, medium-coarse	0.6-0.8
3.	Sand, coarse, with pebbles and stones	0.8-1.0
4.	Loamy sand	0.7-0.85
5.	Loam, light	0.5-0.7
6.	Loam, medium	0.7-0.85
7.	Loam, heavy, with pebbles and stones	0.85-1.05
8.	Clay	0.6-0.8
9.	Wood peat	0.25-0.35
10.	Well decomposed sedge-hypnum and sphagnum peat	0.4-0.6
11.	Poorly decomposed sedge-hypnum peat	0.6-0.8
12.	Poorly decomposed sphagnum peat	0.75-1.05
13.	Poorly decomposed reed-sphagnum peat	0.95-1.30

Table 5

Radius of Curvature of Bends in Diverting Ditch and Water Drain Routes (m)

Hydraulic radius R (m)	0.30	0.50	0.70	0.80	0.90	1.00
Radius of curvature r (m)	20	40	60	70	90	100

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 12
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Average slope of flood embankment slopes

No.	Soil	Slope gradient
		Wet slopes	Dry slopes
1	2	3	4
1.	Clayey	1:1.5-1:2.5	1:1.5-1:2.5
2.	Sandy	1:2-1:3	1:1.5-1:3
3.	Peat-clayey mineral soil mixture	1:10	1:5
4.	Peat-sandy mineral soil mixture	1:12	1:4

Note. Steeper slopes shall be permitted in cohesive foundation soils.

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 13
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Earth dams

Table 1

Average Critical Gradients of Stability Estimates

No.	Soil	Dam body	Upstream blanket	Screen and core
1	2	3	4	5
1.	Clay	7	14	11
2.	Loam	4	9	7
3.	Loamy sand	1.8	2.7	1.8
4.	Sand, medium-coarse	0.9	-	-
5.	Sand, fine	0.7	-	-

Table 2

Types of Fill Dams

No.	Foundation soil	Dam body soil	Recommended dam type
1	2	3	4
1.	Low-permeability	Low-permeability	Of homogeneous material
2.	Low-permeability	Permeable	Of homogeneous material, with a screen
3.	Permeable. Impermeable soil is located at a depth of up to 3 m	Low-permeability	Of homogeneous material, with a recess (tooth)
4.	Permeable. Impermeable soil is located deeper than 3 m	Low-permeability	Of homogeneous material, with an upstream blanket
5.	Permeable. Impermeable soil is located at a depth of up to 3 m	Permeable	Of homogeneous material, with a screen and a recess (barb)
6.	Permeable. Impermeable soil is located deeper than 3 m	Permeable	Of homogeneous material, with a screen and an upstream blanket

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

 

In the wording provided by the Ministry of Economics

Annex 14
to the Latvian Building Code LBN 224-15,
Land Amelioration Systems and Hydrotechnical Structures
(approved by
Cabinet Regulation No. 329
of 30 June 2015)

Fish Protection and Migration Structures

Table 1

Mesh Size of Fish Barrier Nets (mm)

Body length of juvenile fish (mm)	up to 12	15	20	30	40	50	60	70	90
Mesh diameter or panel diagonal length (mm)	1.5	2	3	4	6	7	8	9	10

Table 2

Characteristic Stream Velocities (m/s)

No.	Fish type	Characteristic stream velocities (m/s)
		attraction	sweeping	leaping
1	2	3	4	5
1.	Salmonids, adults	0.9-1.4	1.1-1.6	1.5-2.0
2.	Salmonid spawn	-	0.25-0.35	-
3.	Partially migratory, adults	0.5-0.8	0.9-1.2	-
4.	Partially migratory spawn	-	0.15-0.25	-

Notes.

1. Attraction velocity - the optimal stream velocity that attracts fish to move.

2. Sweeping velocity - the stream velocity which, when exceeded, causes fish to be swept away by the stream.

3. Leaping velocity - the maximum stream velocity that fish are able to overcome for a short period.

Acting for the Minister for Economics,
Minister for Health Guntis Belēvičs

---

Translation © 2026 Valsts valodas centrs (State Language Centre)