SL/T 4-1999 Technical Specification for Farmland Drainage Engineering SL/T 4-1999
Some standard content:
Technical code for farmland drainage project SLT4-1999 Industry standard of the People's Republic of China
Technical code for farmland drainage project
Technical code for farmland drainage projectSL/T4—1999
Editor: China Institute of Water Resources and Hydropower ResearchApproving department: Ministry of Water Resources of the People's Republic of ChinaEffective date: January 1, 2000
Irrigation and Drainage Volume·Comprehensive Technology
Ministry of Water Resources of the People's Republic of China
Notice on the approval and release of "Technical code for farmland drainage project" SL/T4--1999
Shuiguoke [[1999] No. 666
In accordance with the Ministry of Water Resources' plan for the formulation and revision of water conservancy and hydropower technical standards, the "Technical code for farmland drainage project" compiled by the Rural Water Resources Department and China Institute of Water Resources and Hydropower Research as the main editing unit has been reviewed and approved as a water conservancy industry standard and is released. The name and number of the standard are: "Technical Specifications for Farmland Drainage Engineering" SL/T4-1999. After implementation, this standard replaces SL15-90 Technical Specifications for Farmland Drainage (Part on Concealed Pipe Drainage of Farmland in the South). This standard shall be implemented from January 1, 2000. During the implementation process, all units shall pay attention to summarizing experience. If there are any problems, please inform the host department in writing, and it shall be responsible for interpretation. The standard text is published and distributed by China Water Resources and Hydropower Press. On December 3, 1999, according to the "Technical Specifications for Farmland Drainage Engineering (Northern China)" and "Technical Management Regulations for Farmland Water Conservancy Engineering" (later renamed "Technical Specifications for Farmland Drainage Engineering" and "Technical Management Regulations for Irrigation and Drainage Engineering") issued by Document No. 9 (94) Nongshuizongzi, the compilation task of "Technical Specifications for Farmland Drainage Engineering" was presided over by the Rural Water Conservancy Department of the Ministry of Water Resources. The compilation team of "Technical Specifications for Farmland Drainage Engineering" worked according to the standard compilation procedures. After many discussions and revisions, the draft for soliciting opinions and the draft for submission were completed, and a review meeting was held in July 1999, which passed the review. The contents of "Technical Specifications for Farmland Drainage Engineering" are divided into: general principles, planning, design, construction, management, and other provisions, covering all major aspects of farmland drainage engineering technology. Unit for interpreting this code: Rural Water Resources Department of the Ministry of Water Resources. Unit for editing this code: China Institute of Water Resources and Hydropower Research. Units participating in editing this code: Rural Water Resources Department of the Ministry of Water Resources, Farmland Irrigation Research Institute of the Ministry of Water Resources
Wuhan University of Hydraulic and Electric Engineering
Henan Provincial Water Resources Department
Jiangsu Provincial Water Resources Department
Heilongjiang Provincial Agricultural Survey and Design Institute
Guangdong Provincial Water Resources Research Institute
Gansu Irrigation and Drainage Technology Development Company
Ningxia Hui Autonomous Region District Shizuishan Water Conservancy Bureau The main drafters of this specification: Zhang Youyi Li Zhanzhu Shen Rongkai Yao Zhangcun
Shi Fengxia
Li Huiru
Yang Siqian
Luo Huaibin
Jin Qiding
Wang Xiaoling
Nan Yawu
Dong Guanqun
Appendix A
Appendix B
Appendix C
Appendix D
Appendix E
Appendix F
Appendix G
Appendix H
Appendix
Irrigation and drainage volume·Combination technology
Field measurement method of permeability coefficient
Field measurement method of water supply degree.
Field measurement method of rice field leakage rate.
Flooding depth and flooding duration of crops·
Calculation formula of drainage modulus
Critical depth of groundwater·
Calculation formula of the spacing between the last fixed ditch and the suction pipe for regulating the groundwater level , Calculation of average flow velocity of drainage channels and selection of cross-section design parameters Method for determining coefficients related to filling degree in pipeline design Explanation of terms and expressions used in this specification
Explanation of clauses
SL/T4—1999
1 General
1.0.1 This specification is formulated to correctly apply farmland drainage technology, prevent and control waterlogging, waterlogging and soil salinization, ensure project quality, save project costs, improve project benefits, improve ecological environment, and promote sustainable agricultural development. 1.0.2 This specification applies to the planning, design, construction and management of newly built, expanded and rebuilt farmland drainage projects. 1.0.3 Farmland drainage projects should, according to the requirements of project construction, comprehensively collect and analyze the required data, conduct necessary surveys and tests, actively adopt new technologies, new processes and new materials, be consistent with local agricultural and water conservancy zoning, make comprehensive arrangements, and comprehensively manage, and combine advanced irrigation and agricultural technical measures to manage and apply the project to obtain lasting effects of disaster reduction and increased production.
1.0.4 The construction and management of farmland drainage projects must comply with relevant national laws and technical policies. The project construction unit shall hold a design qualification certificate and construction permit that meet the requirements; the project management unit shall strictly implement various management regulations and project maintenance and repair systems.
1.0.5 In addition to complying with this specification, the construction and management of farmland drainage projects shall also comply with the provisions of relevant national standards in force.
2 Planning
2.1 General provisions
2.1.1 Farmland drainage planning should be based on river basin planning, regional water conservancy planning, and the natural, social and economic conditions of the management area, and the current status of water and soil resource utilization. The disaster situation and the causes of poor drainage in the management area should be identified. Based on the requirements of sustainable agricultural development, environmental protection, and comprehensive management of floods, droughts, waterlogging, waterlogging, and salinization, the drainage tasks and drainage standards should be determined, and the overall planning should be carried out in accordance with the principle of overall consideration and storage and drainage. When making specific plans according to the characteristics of different types of governance areas, the following requirements should be met:
1 In plain areas, the drainage system for drainage and groundwater level control should be planned with full consideration of the terrain slope, soil and hydrogeology. In areas where waterlogging and alkali coexist, engineering measures such as ditches, wells, gates, and pumping stations can be adopted. Where conditions permit, measures such as salt washing and waterlogging retention can also be adopted; in areas where waterlogging and flooding coexist, measures such as ditch networks, river networks and drainage pumping stations can be adopted. 2 In arid saline-alkali areas, irrigation and drainage planning should be carried out at the same time according to local natural conditions and salt composition and content, and flushing improvement technology and drainage measures that effectively control groundwater levels should be adopted, and irrigation, agriculture and biology measures should be combined to improve saline-alkali land.
3 The riverside and lakeside embankment areas should adopt engineering measures such as connecting embankments, building stations and gates, and flood control and waterlogging retention according to natural conditions and the hydrology of the inner and outer rivers. On the basis of ensuring the flood control safety of the embankment areas, drainage plans for flood, waterlogging and waterlogging treatment should be formulated in accordance with the principles of separating inner and outer water, setting up irrigation and drainage ditches, separating high and low drainage, and planting water-based and dry crops, as well as the requirements of effectively controlling the water level of the inner river and the groundwater level.
Irrigation and Drainage Volume·Special Technology
4 The coastal tidal areas should take full advantage of the conditions of intertidal self-drainage according to the natural characteristics and tidal laws, and adopt engineering measures such as flood control and tide retention, river regulation, gate construction, flood storage and waterlogging retention. 5 In hilly areas, measures such as building ponds on the top of the hill, flood diversion around the hill, interception at the foot of the hill, field drainage and spring water diversion in the field should be taken according to the terrain, water and soil temperature, slope runoff and underground runoff. At the same time, it should be closely integrated with soil and water conservation, comprehensive development and management planning of hilly areas. In terraced areas, appropriate interception and drainage measures should be taken according to the waterlogging situation of the inner canal.
6 For areas with secondary salinization or secondary waterlogging in the built irrigation area, drainage plans mainly focusing on regulating groundwater levels and necessary monitoring plans should be formulated based on water-salt balance or water volume balance. 7 In flood storage (detention) areas, appropriate and easy-to-repair engineering measures should be selected based on their use probability, land use and farming plans, and production recovery requirements after flood storage (detention). 8 When formulating farmland drainage plans, disaster reduction measures and countermeasures should be proposed and demonstrated for rainfall exceeding the design standard.
The storage and drainage methods, engineering measures and drainage zoning of farmland drainage planning shall comply with the following provisions: 2.1.22
The management area shall fully consider the storage and regulation capacity of reservoirs, ponds, lakes, ditches and soil, and select horizontal or vertical 1
drainage, gravity or pumping drainage and their combined storage and drainage methods according to local conditions. In the embankment area, it is generally required that the water surface rate of flood storage is 5% to 10% of the drainage area, the water depth of regulation is 1~2m, and the water level of flood storage should be 0.20 below the ground.3m. 2 According to the provisions of GB50288-99 "Design Code for Irrigation and Drainage Engineering", the drainage system can usually be divided into four levels: trunk, branch, bucket, and farm. The number of levels can be increased or decreased depending on the size of the treatment area. Among them, the trunk and branch levels that play a role in water transmission should use open ditches. The field drainage projects below the bucket level should select single drainage measures such as open ditches, concealed pipes, rat tunnels, and vertical shafts or combined drainage measures in accordance with local conditions, depending on the causes of waterlogging, waterlogging, and salinization and drainage tasks. 3 When the treatment area is replenished by external surface runoff or underground runoff, it is necessary to lay embankments and ditches in the frontier areas affected by it to intercept floods, intercept flow, or intercept seepage. It is necessary to comply with the basin planning and relevant regulations, and take into account the drainage requirements of upstream and downstream and left and right banks, and no water conservancy conflicts shall be caused.
4 In principle, farmland drainage projects in areas with insufficient water resources should create conditions for drainage reuse. 5 Based on the overall plan, the control area should be divided into drainage zones according to the disaster type, topography, land use, drainage measures and management and application requirements. 2.1.3 The drainage planning of farmland should arrange drainage structures according to the engineering system and drainage control requirements, and should meet the following requirements:
1 Drainage structures should be planned and laid out in the fields in a unified manner with the drainage engineering system. 2 When drainage structures are adjacent to irrigation structures or there are multiple objectives such as transportation and shipping, they should be arranged in a joint manner in accordance with the principles of reasonable layout, convenient use and investment saving. 3 The flood control standards of the gates at the mouth of the embankment area should be consistent with the flood control standards of the outer river embankment. Drainage pump stations should be combined with irrigation as much as possible to implement dual-use of drainage and irrigation. 4
The farmland drainage planning must compare the plans, and the selected planning plan should meet the following requirements: the project is practical, occupies less land and is easy to manage. 1
The project construction investment is low, the operating cost is low and the economic benefit is high. The project is conducive to improving the ecological environment inside and outside the control area and the sustainable development of agriculture. 3
2.1.5 Farmland drainage planning should be based on economic conditions and production development requirements, combining long-term and current planning, engineering measures SL/T4-—1999
and biological measures, and unified planning from the backbone to the intermediate, and formulate an implementation plan. 2.2 Open ditch drainage system
2.2.1 The open ditch drainage system consists of drainage open ditches at all levels, their buildings and receiving and discharging areas. The number of open ditches should be determined in accordance with Article 2.1.2 of this specification. In areas with serious waterlogging, collapse and salinization, various temporary auxiliary drainage measures such as hair ditches and rat paths can be added. 2.2.2 The layout form and line selection of drainage open ditches should meet the following requirements: 1 Drainage open ditches should be arranged in combination with irrigation canals and field roads. In areas with flat terrain, it is advisable to adopt the same two-way drainage form as irrigation channels; in inclined plain areas, it is advisable to adopt a one-way drainage form adjacent to irrigation channels. In light soil areas, roads or forest belts should be arranged between adjacent canals and ditches; when mechanical silt removal is required, the arrangement form of adjacent roads and ditches should be adopted.
2 The routes of open drainage ditches at all levels should be selected according to the terrain conditions of the treatment area, in accordance with the principles of high drainage for high water, low drainage for low water, drainage nearby, and striving for self-flow, and the following regulations: 1) In principle, open drainage ditches at all levels should be arranged along low-lying waterlogging lines, and natural rivers should be used as much as possible. 2) Branch ditches and main ditches, main ditches and natural rivers should be connected at an acute angle, and branch ditches, ditch ditches and agricultural ditches should be connected vertically to each other. 3) The routes of open drainage ditches at all levels should be selected in soil zones that are conducive to ditch slope stability. If it is necessary to pass through unstable soil zones, measures to prevent ditch slope collapse should be proposed, and simple anti-collapse treatment or other drainage measures should be used for ditch ditches and agricultural ditches. 4) When the terrain slope is greater than 0.5%, the final fixed ditch should be arranged roughly along the terrain contour line. 2.2.3 The selection of drainage receiving and discharging areas and the treatment of drainage outlets shall comply with the following provisions: 1 The drainage receiving and discharging areas shall ensure that the outflow conditions of the drainage system have stable river channels or tidal beds, safe embankments and sufficient discharge capacity, and do not cause environmental damage. 2 When the design water level of the drainage outlet is lower than the water level of the receiving and discharging area at the same period or frequency, or when the water level of the next level drainage ditch is supported and cannot be drained by gravity, a pumping station shall be set up. If gravity drainage is only not possible for part of the time, drainage engineering facilities combining gravity and pumping can be adopted.
2.3 Concealed pipe drainage engineering
2.3.1 The field concealed pipe drainage engineering generally consists of a suction pipe, a water collection pipe (ditch), ancillary buildings and drainage outlets, and shall meet the following requirements:
1 The suction pipe should have good groundwater absorption and water transmission capabilities; the water collection pipe (ditch) should be able to collect and discharge the water from the suction pipe in time.
2Depending on the specific situation, the concealed pipe drainage project shall be equipped with inspection wells, concealed pipe gates, water collection wells and other ancillary buildings. 3The drainage outlet of the field concealed pipe drainage project is usually an open ditch system, which should ensure smooth drainage and stable channels. The drainage outlet when forming a concealed pipe drainage system shall comply with the provisions of 2.2.3 of this specification. 2.3.2The composition, classification and pipe type and specifications of the concealed pipe drainage system shall be determined based on the drainage scale, drainage requirements, terrain, soil quality, pipe materials, filter materials and construction conditions, and after technical and economic comparison. 2.3.3The layout of the concealed pipe drainage project shall comply with the following provisions: 1The plane layout of concealed pipes in plain areas:
1) In flat terrain areas, it is advisable to use suction pipes on both sides of the water collection pipe (ditch) in the form of orthogonal or acute angle oblique intersection; in gentle slope areas, when the drainage ditch adjacent to the irrigation and drainage is used as the water collection ditch, it is advisable to use suction pipes on one side of the water collection ditch in the form of orthogonal or acute angle 268
oblique intersection.
Irrigation and Drainage Volume·Comprehensive Technology
2) In the plain area, the suction pipes should be laid out at equal intervals and perpendicular to the groundwater flow direction or at a large angle. 3) In paddy fields or water-dry rotation areas, a suction pipe should be laid in the same field. When the elevations of adjacent fields are similar and the crops are the same, they can be laid across the fields.
2 Plane layout of underground pipes in hilly areas:
1) The suction pipes in the Chongcheng field should be laid out roughly along the terrain contours and at equal intervals. The water collection ditch should be laid in the middle of the farmland or around the field depending on the terrain conditions.
2) The number of suction pipes and their spacing at the inner bank of the terraced field should be determined by the width and degree of collapse of the inner bank and the scope of action of the suction pipes.
3) When there is a spring in the field, the location and water volume of the spring should be found out first, and a spring guide underground pipe (culvert) should be set to directly guide the spring water into the water collection pipe (ditch). If necessary, a reverse filter should be installed at the spring eye and connected to the spring guide pipe. Then, field suction pipes should be laid out as needed.
3 Inspection wells should generally be set at the intersection of pipelines, pipeline corners and gradient mutations, as well as on both sides or downstream sides of crossing ditches, canals and roads. When the pipeline is long, an inspection well should be set up every 200-300m. 4 When the outlet of the suction pipe in paddy fields or water-planting rotation areas is an open ditch, control gates should usually be set one by one or multiple times in combination according to the requirements of drainage regulation. For areas with flat terrain and the same crop types, gates should be set at the outlet of the water collection pipe (ditch) for zoned drainage control.
5 When there is no gravity drainage condition in the dark pipe drainage treatment area, centralized or segmented drainage should be adopted depending on the specific conditions of the project. 6 The starting end of the suction pipe should not be less than 3m away from the irrigation channel. 2.4 Vertical and other drainage projects
2.4.1 In areas where the water quality and water discharge conditions of the aquifer are good, vertical drainage can be adopted, and well irrigation and well drainage can be implemented to control the groundwater level and comprehensively prevent and control drought, waterlogging and salinization disasters. The planning and layout of vertical wells should comply with the current national SD188-86 "Technical Specifications for Agricultural Wells" and the requirements of local water conservancy planning. 2.4.2 Ratways (including line seam trenches) are suitable for field waterlogging control and drainage in clay soil areas where there are no large pebbles within the construction depth. The use of ratway drainage should meet the following requirements: 1 Ratways should be laid out in parallel with each other and should have good drainage outlets. 2 The water discharged from ratways generally flows into the water collection ditch. If it needs to flow into the underground pipe, a filter layer must be set at the intersection. 3 For ratways that have been used for many years, horizontal pipes should be buried at the head of each field to connect multiple ratways, concentrate them at one outlet to the water collection ditch, and set up drainage control facilities as needed. 2.4.3 Combined drainage should be selected according to the treatment requirements and specific conditions, and meet the following requirements: 1 In areas where waterlogging, waterlogging, and salinization are being treated, a drainage system combining open ditches and concealed pipes can be selected based on soil quality, topography, treatment requirements, and technical and economic conditions, and its layout should be conducive to comprehensive treatment. 2 In areas where drought, waterlogging, and salinization are being treated and shallow fresh water is used for irrigation, a drainage system combining well irrigation, well drainage, and open ditches can be used for comprehensive treatment. In shallow brackish and semi-salty water areas with surface irrigation or rainfall infiltration recharge conditions, open ditches and vertical wells can also be used to pump water from vertical wells for irrigation, or irrigate after desalination, or discharge salt water that is not suitable for use out of the area.
3 When using underground pipe drainage to treat flooding in clay soil areas, temporary shallow open ditches, rat paths or line SL/T4—1999
seam ditches can be added in the field to form a combination of drainage with the same depth or intersecting layout, and it is advisable to assist with measures such as loosening and improving the soil to enhance the drainage effect.
2.4.4 The comprehensive utilization of drainage projects must pass feasibility demonstration and comply with the following provisions: 1 When using drainage open ditches to collect water and convey water for irrigation, the flexibility of the project system scheduling and operation must be considered, and effective measures must be taken to prevent the occurrence or aggravation of waterlogging, waterlogging, and salinization disasters on both sides of the river caused by siltation in the ditches, slope collapse, and excessive water levels.
2 When using drainage ditch networks to build gates to store water and replenish groundwater, it is advisable to select ditch network areas or ditch sections with good soil permeability, and the relationship between water storage and recharging and normal drainage should be handled well to prevent secondary salinization and waterlogging disasters of the soil. Sewage with excessive water quality and muddy water containing silt shall not be used for recharging. 3 When using drainage ditch networks for aquaculture and water transportation, the water depth and water surface width can be determined according to relevant regulations. It is strictly forbidden to block water at every step on the drainage ditch network, and the necessary additional ancillary facilities shall not affect normal drainage. 3 Design
3.1 General provisions
3.1.1 The design drainage standard should be selected for the treatment area according to the drainage task. If the local economic conditions are good or there are special requirements, the standards can be appropriately raised; if limited by conditions, the standards can be met by phased implementation. 3.1.2 In drainage design, the design elements of dikes, pumping stations and other drainage projects should be determined in accordance with the flood control plan of the basin or region and the provisions of GB50201-94 "Flood Control Standards". 3.1.3 The preparation of design documents for agricultural drainage projects and the analysis of project investment and economic benefits should be carried out in accordance with the relevant design report preparation procedures for water conservancy and hydropower projects and SL72-94 "Economic Evaluation Code for Water Conservancy Construction Projects" and other relevant standards. 3.1.4 Parameters such as the permeability coefficient of the soil layer in the treatment area, water supply degree and paddy field leakage rate should be determined in accordance with Appendices A to C of this specification.
3.2 Drainage standards
3.2.1 The drainage standards for farmland can be divided into three categories: drainage, waterlogging control and salinization prevention and control. They should be determined through technical and economic demonstration based on drainage test data or practical experience in local or similar areas, in accordance with factors such as crop types, soil characteristics, hydrogeological and meteorological conditions in the control area, and in combination with social and economic conditions and agricultural development levels, and should comply with the relevant provisions of this section.
3.2.2 The determination of drainage standards should comply with the following provisions: 1 The design rainstorm recurrence period can be 5 to 10 years. 2 The duration and discharge time of the design rainstorm should be determined based on the rainstorm characteristics, confluence conditions, river network and lake regulation and storage capacity, the flooding depth and flooding duration of crops (selected according to Appendix D of this specification) and relevant analysis of crop yield reduction rate in the control area. In the rice-growing area, 1 to 3 days of 13-day rainstorm can be used for drainage. In the rice-growing area, 3 to 5 days of 13-day rainstorm can be used to drain to the water depth.
3 The drainage modulus should be determined based on the measured data of the local or neighboring areas in the near future. If there is no measured data, it can be determined based on the specific conditions of the treatment area, using the method approved by the basin organization or using the appropriate formula in Appendix E of this specification.
The drainage standard for waterlogging treatment should be determined based on the requirements of crop growth and agricultural machinery operation, and meet the following requirements: 3.2.3
1 The maximum drainage depth required for waterlogging treatment and drainage engineering should be used as the engineering control standard to meet the requirements of the entire growth period of crops. Generally, 0.8~1.3m can be selected depending on the root depth of the crop. In the early cropping area, the groundwater depth can be reduced to 0.4~0.6m within 3~4d during the sensitive period of waterlogging; in the late cropping area, it can be reduced to 0.4~0.6m within 3~5d during the field drying period; the appropriate leakage rate during the flooding period can be selected from 2~8mm/d, with a smaller value for clay soil and a larger value for sandy soil. 2 The drainage depth required for agricultural machinery operation should generally be controlled at 0.6-0.8m, and the drainage time can be determined according to the farming requirements of various places.
3 The drainage modulus for flood control can be calculated using the following formula:
Where q is the drainage modulus for flood control required for groundwater level regulation, m/d; A is the average drop in groundwater level required to meet flood control requirements, m; t is the drainage time, d, which should be determined according to the flood control requirements in this article. μ is the average water supply within the range of groundwater level drop. 3.2.4 The determination of drainage standards for preventing and controlling salinization should comply with the following provisions: (3.2.3-1)
1 The critical depth of groundwater (selected according to Appendix F of this specification) should usually be used as the engineering design standard. When a design less than the critical depth is used, it should be determined through water-salt balance demonstration. 2 The drainage time for preventing and controlling salinization can generally be 8 to 15 days to lower the groundwater level to the critical depth and meet the following requirements:
1) In areas for preventing salinization, the salt content of the root layer soil during each growth period of crops should be ensured not to exceed their salt tolerance. 2) In areas for flushing and improving saline-alkali soil, the desalination requirements should be met within the designed soil layer depth. 3 The drainage modulus for preventing and controlling salinization and the drainage modulus for flushing and improvement can be determined by the following formulas: When preventing and controlling salinization
When flushing and improving
q - m(h,- ha) - c.
q - m- ef - Aw - -
e, = el1 - ho,th)
wherein: average evaporation intensity of groundwater during drainage, m/d; (3.2.4-1)
(3.2.4-2)
(3.2.4-3)
eo——water surface evaporation intensity, m/d. If the evaporation effect can be ignored according to local conditions, it should be taken as =0;
ho—initial groundwater depth, m;
h,—design groundwater depth, m. The critical value can usually be used. Depth substitution; h, the depth at which groundwater stops evaporating or evaporates weakly, m; n, the index of the relationship between groundwater evaporation and burial depth, usually n≥1; 0, the correction coefficient of the shape of the groundwater surface in the drainage section, usually 0.7-0.8 for open ditches and 0.8-0.9 for concealed pipes; m, flushing quota, m;
SL/T4-1999
w, the increment of soil moisture content before and after flushing drainage, m; t, the drainage time or flushing drainage time to prevent soil salt return, d. 3.3 Open ditch drainage
3.3.1 The design flow of open ditch drainage at all levels should be calculated according to the control area and runoff conditions according to the design standards, or it can be determined by multiplying the drainage modulus corresponding to the drainage task by its control area, and should comply with the following provisions: 1 For ditches with a single drainage task, the drainage design flow should be determined according to the requirements of drainage, waterlogging control or prevention and control of salinization. When there is a flushing requirement in salinized areas, the flushing drainage flow should be used as the verification flow. 2 In areas where waterlogging, waterlogging and salinization coexist, the drainage flow for drainage, waterlogging control and salinization prevention and control should be determined according to the design standards, and the design flow and verification flow should be selected from them. 3 For the comprehensive utilization of drainage, diversion, storage and irrigation, the flow requirements of other utilization methods should also be considered under the condition of meeting the drainage design flow. bzxz.net
3.3.2 The depth and spacing of the final fixed ditch should be determined according to the drainage standards corresponding to the drainage task, and should meet the following requirements:
1 The spacing of the final fixed ditch for drainage should be selected according to the terrain conditions, farming requirements, field size and field irrigation channels, and the ditch depth should be determined according to the cross-section design calculation. 2 The depth of the final fixed ditch for regulating the groundwater level can be calculated by the following formula: h. =h+AH+ha
Where h. —The depth of the last fixed ditch for controlling the groundwater level, m; h——Drainage depth or critical depth, m;
△H——Residual head or stagnant head, m, generally 0.2～0.3m; h. —The depth of water in the ditch when draining groundwater, m, generally 0.1～0.2m. 3 The spacing of the last fixed ditch for controlling the groundwater level can be determined by the following three methods: 1) Drainage test method, determined according to the requirements of SL109-95 "Agricultural Drainage Test Specification"; 2) Formula calculation method, determined by selecting appropriate formulas according to Appendix G of this specification; 3) Empirical numerical method, selected according to the empirical value determined by local or similar areas' practical experience. (3.3.2-1)
4 The last fixed ditch for both drainage and groundwater level control should generally determine the ditch depth and spacing according to the requirements of groundwater level control, and determine the cross-section according to the drainage design flow, slope stability and construction requirements. 3.3.3 The cross-sectional design of drainage ditches shall meet the basic requirements of water conveyance capacity, water level control, water level connection between upper and lower ditches and buildings, slope stability, no erosion and siltation, small amount of engineering work, and convenience for manual construction or mechanical operation, and shall comply with the following provisions:
1 The flow cross-section of the drainage ditch shall be determined by calculation based on the design flow rate, and the relevant design parameters shall be selected in accordance with Appendix H of this Code. 2 When the depth of the drainage ditch is greater than 5m, a compound cross-section that is convenient for construction and management shall be adopted. A platform with a width of not less than 0.8m may be provided at a depth of 3 to 5m above the bottom of the ditch. 3 The water level connection of drainage ditches at the intersection: 1) When the design flow rate passes, the water level of the lower ditch shall be 0.1 to 0.2m lower than the water level of the upper ditch; 2) When the verification flow rate passes, the lower ditch is allowed to temporarily support the upper ditch with a water level;2m; 2) When checking the flow, the lower channel is allowed to temporarily support the upper channel with water level;2m; 2) When checking the flow, the lower channel is allowed to temporarily support the upper channel with water level;2m; 2) When checking the flow, the lower channel is allowed to temporarily support the upper channel with water level;2m; 2) When checking the flow, the lower channel is allowed to temporarily support the upper channel with water level;1 General Provisions
3.1.1 The design drainage standard for the treatment area should be selected according to the drainage task. If the local economic conditions are good or there are special requirements, the standard can be appropriately raised; if limited by conditions, it can be implemented in stages to achieve the standard. 3.1.2 In the drainage design, the design elements of the dike, pump station and other drainage projects should be determined according to the flood control plan of the basin or region and the provisions of GB50201-94 "Flood Control Standards". 3.1.3 The preparation of design documents for agricultural drainage projects and the analysis of project investment and economic benefits should be carried out in accordance with the relevant design report preparation procedures for water conservancy and hydropower projects and SL72-94 "Economic Evaluation Code for Water Conservancy Construction Projects" and other relevant standards. 3.1.4 Parameters such as the permeability coefficient, water supply degree and rice field leakage rate of the soil layer in the treatment area should be determined according to Appendix A to Appendix C of this specification.
3.2 Drainage standards
3.2.1 The drainage standards for farmland can be divided into three categories: drainage, waterlogging control and salinization prevention and control. They should be determined through technical and economic demonstration based on drainage test data or practical experience in local or similar areas, in accordance with factors such as crop types, soil characteristics, hydrogeological and meteorological conditions in the control area, and in combination with social and economic conditions and agricultural development levels, and should comply with the relevant provisions of this section.
3.2.2 The determination of drainage standards should comply with the following provisions: 1 The design rainstorm recurrence period can be 5 to 10 years. 2 The duration and discharge time of the design rainstorm should be determined based on the rainstorm characteristics, confluence conditions, river network and lake regulation and storage capacity, the flooding depth and flooding duration of crops (selected according to Appendix D of this specification) and relevant analysis of crop yield reduction rate in the control area. In the rice-growing area, 1 to 3 days of 13-day rainstorm can be used for drainage. In the rice-growing area, 3 to 5 days of 13-day rainstorm can be used to drain to the water depth.
3 The drainage modulus should be determined based on the measured data of the local or neighboring areas in the near future. If there is no measured data, it can be determined based on the specific conditions of the treatment area, using the method approved by the basin organization or using the appropriate formula in Appendix E of this specification.
The drainage standard for waterlogging treatment should be determined based on the requirements of crop growth and agricultural machinery operation, and meet the following requirements: 3.2.3
1 The maximum drainage depth required for waterlogging treatment and drainage engineering should be used as the engineering control standard to meet the requirements of the entire growth period of crops. Generally, 0.8~1.3m can be selected depending on the root depth of the crop. In the early cropping area, the groundwater depth can be reduced to 0.4~0.6m within 3~4d during the sensitive period of waterlogging; in the late cropping area, it can be reduced to 0.4~0.6m within 3~5d during the field drying period; the appropriate leakage rate during the flooding period can be selected from 2~8mm/d, with a smaller value for clay soil and a larger value for sandy soil. 2 The drainage depth required for agricultural machinery operation should generally be controlled at 0.6-0.8m, and the drainage time can be determined according to the farming requirements of various places.
3 The drainage modulus for flood control can be calculated using the following formula:
Where q is the drainage modulus for flood control required for groundwater level regulation, m/d; A is the average drop in groundwater level required to meet flood control requirements, m; t is the drainage time, d, which should be determined according to the flood control requirements in this article. μ is the average water supply within the range of groundwater level drop. 3.2.4 The determination of drainage standards for preventing and controlling salinization should comply with the following provisions: (3.2.3-1)
1 The critical depth of groundwater (selected according to Appendix F of this specification) should usually be used as the engineering design standard. When a design less than the critical depth is used, it should be determined through water-salt balance demonstration. 2 The drainage time for preventing and controlling salinization can generally be 8 to 15 days to lower the groundwater level to the critical depth and meet the following requirements:
1) In areas for preventing salinization, the salt content of the root layer soil during each growth period of crops should be ensured not to exceed their salt tolerance. 2) In areas for flushing and improving saline-alkali soil, the desalination requirements should be met within the designed soil layer depth. 3 The drainage modulus for preventing and controlling salinization and the drainage modulus for flushing and improvement can be determined by the following formulas: When preventing and controlling salinization
When flushing and improving
q - m(h,- ha) - c.
q - m- ef - Aw - -
e, = el1 - ho,th)
wherein: average evaporation intensity of groundwater during drainage, m/d; (3.2.4-1)
(3.2.4-2)
(3.2.4-3)
eo——water surface evaporation intensity, m/d. If the evaporation effect can be ignored according to local conditions, it should be taken as =0;
ho—initial groundwater depth, m;
h,—design groundwater depth, m. The critical value can usually be used. Depth substitution; h, the depth at which groundwater stops evaporating or evaporates weakly, m; n, the index of the relationship between groundwater evaporation and burial depth, usually n≥1; 0, the correction coefficient of the shape of the groundwater surface in the drainage section, usually 0.7-0.8 for open ditches and 0.8-0.9 for concealed pipes; m, flushing quota, m;
SL/T4-1999
w, the increment of soil moisture content before and after flushing drainage, m; t, the drainage time or flushing drainage time to prevent soil salt return, d. 3.3 Open ditch drainage
3.3.1 The design flow of open ditch drainage at all levels should be calculated according to the control area and runoff conditions according to the design standards, or it can be determined by multiplying the drainage modulus corresponding to the drainage task by its control area, and should comply with the following provisions: 1 For ditches with a single drainage task, the drainage design flow should be determined according to the requirements of drainage, waterlogging control or prevention and control of salinization. When there is a flushing requirement in salinized areas, the flushing drainage flow should be used as the verification flow. 2 In areas where waterlogging, waterlogging and salinization coexist, the drainage flow for drainage, waterlogging control and salinization prevention and control should be determined according to the design standards, and the design flow and verification flow should be selected from them. 3 For the comprehensive utilization of drainage, diversion, storage and irrigation, the flow requirements of other utilization methods should also be considered under the condition of meeting the drainage design flow.
3.3.2 The depth and spacing of the final fixed ditch should be determined according to the drainage standards corresponding to the drainage task, and should meet the following requirements:
1 The spacing of the final fixed ditch for drainage should be selected according to the terrain conditions, farming requirements, field size and field irrigation channels, and the ditch depth should be determined according to the cross-section design calculation. 2 The depth of the final fixed ditch for regulating the groundwater level can be calculated by the following formula: h. =h+AH+ha
Where h. —The depth of the last fixed ditch for controlling the groundwater level, m; h——Drainage depth or critical depth, m;
△H——Residual head or stagnant head, m, generally 0.2～0.3m; h. —The depth of water in the ditch when draining groundwater, m, generally 0.1～0.2m. 3 The spacing of the last fixed ditch for controlling the groundwater level can be determined by the following three methods: 1) Drainage test method, determined according to the requirements of SL109-95 "Agricultural Drainage Test Specification"; 2) Formula calculation method, determined by selecting appropriate formulas according to Appendix G of this specification; 3) Empirical numerical method, selected according to the empirical value determined by local or similar areas' practical experience. (3.3.2-1)
4 The last fixed ditch for both drainage and groundwater level control should generally determine the ditch depth and spacing according to the requirements of groundwater level control, and determine the cross-section according to the drainage design flow, slope stability and construction requirements. 3.3.3 The cross-sectional design of drainage ditches shall meet the basic requirements of water conveyance capacity, water level control, water level connection between upper and lower ditches and buildings, slope stability, no scouring and silting, small amount of engineering work, and convenience for manual construction or mechanical operation, and shall comply with the following provisions:
1 The flow cross-section of the drainage ditch shall be determined by calculation according to the design flow rate, and the relevant design parameters shall be selected according to Appendix H of this Code. 2 When the depth of the drainage ditch is greater than 5m, a compound cross-section that is convenient for construction and management shall be adopted. A platform with a width of not less than 0.8m may be set at a depth of 3 to 5m above the bottom of the ditch. 3 The water level connection of drainage ditches at the intersection: 1) When the design flow rate passes, the water level of the lower ditch shall be 0.1 to 0.2m lower than the water level of the upper ditch; 2) When the verification flow rate passes, the lower ditch is allowed to temporarily support the upper ditch with a water level;1 General Provisions
3.1.1 The design drainage standard for the treatment area should be selected according to the drainage task. If the local economic conditions are good or there are special requirements, the standard can be appropriately raised; if limited by conditions, it can be implemented in stages to achieve the standard. 3.1.2 In the drainage design, the design elements of the dike, pump station and other drainage projects should be determined according to the flood control plan of the basin or region and the provisions of GB50201-94 "Flood Control Standards". 3.1.3 The preparation of design documents for agricultural drainage projects and the analysis of project investment and economic benefits should be carried out in accordance with the relevant design report preparation procedures for water conservancy and hydropower projects and SL72-94 "Economic Evaluation Code for Water Conservancy Construction Projects" and other relevant standards. 3.1.4 Parameters such as the permeability coefficient, water supply degree and rice field leakage rate of the soil layer in the treatment area should be determined according to Appendix A to Appendix C of this specification.
3.2 Drainage standards
3.2.1 The drainage standards for farmland can be divided into three categories: drainage, waterlogging control and salinization prevention and control. They should be determined through technical and economic demonstration based on drainage test data or practical experience in local or similar areas, in accordance with factors such as crop types, soil characteristics, hydrogeological and meteorological conditions in the control area, and in combination with social and economic conditions and agricultural development levels, and should comply with the relevant provisions of this section.
3.2.2 The determination of drainage standards should comply with the following provisions: 1 The design rainstorm recurrence period can be 5 to 10 years. 2 The duration and discharge time of the design rainstorm should be determined based on the rainstorm characteristics, confluence conditions, river network and lake regulation and storage capacity, the flooding depth and flooding duration of crops (selected according to Appendix D of this specification) and relevant analysis of crop yield reduction rate in the control area. In the rice-growing area, 1 to 3 days of 13-day rainstorm can be used for drainage. In the rice-growing area, 3 to 5 days of 13-day rainstorm can be used to drain to the water depth.
3 The drainage modulus should be determined based on the measured data of the local or neighboring areas in the near future. If there is no measured data, it can be determined based on the specific conditions of the treatment area, using the method approved by the basin organization or using the appropriate formula in Appendix E of this specification.
The drainage standard for waterlogging treatment should be determined based on the requirements of crop growth and agricultural machinery operation, and meet the following requirements: 3.2.3
1 The maximum drainage depth required for waterlogging treatment and drainage engineering should be used as the engineering control standard to meet the requirements of the entire growth period of crops. Generally, 0.8~1.3m can be selected depending on the root depth of the crop. In the early cropping area, the groundwater depth can be reduced to 0.4~0.6m within 3~4d during the sensitive period of waterlogging; in the late cropping area, it can be reduced to 0.4~0.6m within 3~5d during the field drying period; the appropriate leakage rate during the flooding period can be selected from 2~8mm/d, with a smaller value for clay soil and a larger value for sandy soil. 2 The drainage depth required for agricultural machinery operation should generally be controlled at 0.6-0.8m, and the drainage time can be determined according to the farming requirements of various places.
3 The drainage modulus for flood control can be calculated using the following formula:
Where q is the drainage modulus for flood control required for groundwater level regulation, m/d; A is the average drop in groundwater level required to meet flood control requirements, m; t is the drainage time, d, which should be determined according to the flood control requirements in this article. μ is the average water supply within the range of groundwater level drop. 3.2.4 The determination of drainage standards for preventing and controlling salinization should comply with the following provisions: (3.2.3-1)
1 The critical depth of groundwater (selected according to Appendix F of this specification) should usually be used as the engineering design standard. When a design less than the critical depth is used, it should be determined through water-salt balance demonstration. 2 The drainage time for preventing and controlling salinization can generally be 8 to 15 days to lower the groundwater level to the critical depth and meet the following requirements:
1) In areas for preventing salinization, the salt content of the root layer soil during each growth period of crops should be ensured not to exceed their salt tolerance. 2) In areas for flushing and improving saline-alkali soil, the desalination requirements should be met within the designed soil layer depth. 3 The drainage modulus for preventing and controlling salinization and the drainage modulus for flushing and improvement can be determined by the following formulas: When preventing and controlling salinization
When flushing and improving
q - m(h,- ha) - c.
q - m- ef - Aw - -
e, = el1 - ho,th)
wherein: average evaporation intensity of groundwater during drainage, m/d; (3.2.4-1)
(3.2.4-2)
(3.2.4-3)
eo——water surface evaporation intensity, m/d. If the evaporation effect can be ignored according to local conditions, it should be taken as =0;
ho—initial groundwater depth, m;
h,—design groundwater depth, m. The critical value can usually be used. Depth substitution; h, the depth at which groundwater stops evaporating or evaporates weakly, m; n, the index of the relationship between groundwater evaporation and burial depth, usually n≥1; 0, the correction coefficient of the shape of the groundwater surface in the drainage section, usually 0.7-0.8 for open ditches and 0.8-0.9 for concealed pipes; m, flushing quota, m;
SL/T4-1999
w, the increment of soil moisture content before and after flushing drainage, m; t, the drainage time or flushing drainage time to prevent soil salt return, d. 3.3 Open ditch drainage
3.3.1 The design flow of open ditch drainage at all levels should be calculated according to the control area and runoff conditions according to the design standards, or it can be determined by multiplying the drainage modulus corresponding to the drainage task by its control area, and should comply with the following provisions: 1 For ditches with a single drainage task, the drainage design flow should be determined according to the requirements of drainage, waterlogging control or prevention and control of salinization. When there is a flushing requirement in salinized areas, the flushing drainage flow should be used as the verification flow. 2 In areas where waterlogging, waterlogging and salinization coexist, the drainage flow for drainage, waterlogging control and salinization prevention and control should be determined according to the design standards, and the design flow and verification flow should be selected from them. 3 For the comprehensive utilization of drainage, diversion, storage and irrigation, the flow requirements of other utilization methods should also be considered under the condition of meeting the drainage design flow.
3.3.2 The depth and spacing of the final fixed ditch should be determined according to the drainage standards corresponding to the drainage task, and should meet the following requirements:
1 The spacing of the final fixed ditch for drainage should be selected according to the terrain conditions, farming requirements, field size and field irrigation channels, and the ditch depth should be determined according to the cross-section design calculation. 2 The depth of the final fixed ditch for regulating the groundwater level can be calculated by the following formula: h. =h+AH+ha
Where h. —The depth of the last fixed ditch for controlling the groundwater level, m; h——Drainage depth or critical depth, m;
△H——Residual head or stagnant head, m, generally 0.2～0.3m; h. —The depth of water in the ditch when draining groundwater, m, generally 0.1～0.2m. 3 The spacing of the last fixed ditch for controlling the groundwater level can be determined by the following three methods: 1) Drainage test method, determined according to the requirements of SL109-95 "Agricultural Drainage Test Specification"; 2) Formula calculation method, determined by selecting appropriate formulas according to Appendix G of this specification; 3) Empirical numerical method, selected according to the empirical value determined by local or similar areas' practical experience. (3.3.2-1)
4 The last fixed ditch for both drainage and groundwater level control should generally determine the ditch depth and spacing according to the requirements of groundwater level control, and determine the cross-section according to the drainage design flow, slope stability and construction requirements. 3.3.3 The cross-sectional design of drainage ditches shall meet the basic requirements of water conveyance capacity, water level control, water level connection between upper and lower ditches and buildings, slope stability, no erosion and siltation, small amount of engineering work, and convenience for manual construction or mechanical operation, and shall comply with the following provisions:
1 The flow cross-section of the drainage ditch shall be determined by calculation based on the design flow rate, and the relevant design parameters shall be selected in accordance with Appendix H of this Code. 2 When the depth of the drainage ditch is greater than 5m, a compound cross-section that is convenient for construction and management shall be adopted. A platform with a width of not less than 0.8m may be provided at a depth of 3 to 5m above the bottom of the ditch. 3 The water level connection of drainage ditches at the intersection: 1) When the design flow rate passes, the water level of the lower ditch shall be 0.1 to 0.2m lower than the water level of the upper ditch; 2) When the verification flow rate passes, the lower ditch is allowed to temporarily support the upper ditch with a water level;1 The farmland drainage standards can be divided into three categories: drainage, waterlogging control and salinization prevention and control. All of them should be determined through technical and economic demonstration based on drainage test data or practical experience in local or similar areas, in accordance with factors such as crop types, soil characteristics, hydrogeological and meteorological conditions in the control area, combined with social and economic conditions and agricultural development level, and should comply with the relevant provisions of this section.
3.2.2 The determination of drainage standards should comply with the following provisions: 1 The design rainstorm recurrence period can be 5 to 10 years. 2 The duration and drainage time of the design rainstorm should be determined based on the rainstorm characteristics, confluence conditions, river network and lake regulation capacity, flooding tolerance depth and flooding duration of crops (selected according to Appendix D of this specification) and relevant analysis of crop yield reduction rate in the control area. For the rice-growing area, 1 to 3 days of 13-day rainstorm can be used for drainage. For the rice-growing area, 3 to 5 days of 13-day rainstorm can be used to drain to the water tolerance depth.
3 The drainage modulus should be determined based on the measured data of the local or neighboring areas in the recent period. When there is no measured data, the specific conditions of the watershed area can be determined by using the method approved by the basin organization or by using the appropriate formula in Appendix E of this specification. The waterlogging control and drainage standard should be determined by comprehensively considering the requirements of crop growth and agricultural machinery operation, and meet the following requirements: 3.2.3
1 The waterlogging control and drainage project should take the maximum drainage depth that meets the requirements of the entire growth period of crops as the engineering control standard, which can generally be selected from 0.8 to 1.3 m depending on the root depth of the crop. In the early cropping area, the groundwater depth can be reduced to 0.4 to 0.6 m within 3 to 4 days during the sensitive period of flooding; in the late cropping area, the groundwater depth can be reduced to 0.4 to 0.6 m within 3 to 5 days during the field drying period; the appropriate leakage rate during the flooding period can be selected from 2 to 8 mm/d, with a smaller value for clay soil and a larger value for sandy soil. 2 The drainage depth required for agricultural machinery operation should generally be controlled at 0.6-0.8m, and the drainage time can be determined according to the farming requirements of various places.
3 The drainage modulus for flood control can be calculated using the following formula:
Where q is the drainage modulus for flood control required for groundwater level regulation, m/d; A is the average drop in groundwater level required to meet flood control requirements, m; t is the drainage time, d, which should be determined according to the flood control requirements in this article. μ is the average water supply within the range of groundwater level drop. 3.2.4 The determination of drainage standards for preventing and controlling salinization should comply with the following provisions: (3.2.3-1)
1 The critical depth of groundwater (selected according to Appendix F of this specification) should usually be used as the engineering design standard. When a design less than the critical depth is used, it should be determined through water-salt balance demonstration. 2 The drainage time for preventing and controlling salinization can generally be 8 to 15 days to lower the groundwater level to the critical depth and meet the following requirements:
1) In areas for preventing salinization, the salt content of the root layer soil during each growth period of crops should be ensured not to exceed their salt tolerance. 2) In areas for flushing and improving saline-alkali soil, the desalination requirements should be met within the designed soil layer depth. 3 The drainage modulus for preventing and controlling salinization and the drainage modulus for flushing and improvement can be determined by the following formulas: When preventing and controlling salinization
When flushing and improving
q - m(h,- ha) - c.
q - m- ef - Aw - -
e, = el1 - ho,th)
wherein: average evaporation intensity of groundwater during drainage, m/d; (3.2.4-1)
(3.2.4-2)
(3.2.4-3)
eo——water surface evaporation intensity, m/d. If the influence of evaporation can be ignored according to local conditions, it should be taken as =0;
ho—initial groundwater depth, m;
h,—design groundwater depth, m. The critical value can usually be used. Depth substitution; h, the depth at which groundwater stops evaporating or evaporates weakly, m; n, the index of the relationship between groundwater evaporation and burial depth, usually n≥1; 0, the correction coefficient of the shape of the groundwater surface in the drainage section, usually 0.7-0.8 for open ditches and 0.8-0.9 for concealed pipes; m, flushing quota, m;
SL/T4-1999
w, the increment of soil moisture content before and after flushing drainage, m; t, the drainage time or flushing drainage time to prevent soil salt return, d. 3.3 Open ditch drainage
3.3.1 The design flow of open ditch drainage at all levels should be calculated according to the control area and runoff conditions according to the design standards, or it can be determined by multiplying the drainage modulus corresponding to the drainage task by its control area, and should comply with the following provisions: 1 For ditches with a single drainage task, the drainage design flow should be determined according to the requirements of drainage, waterlogging control or prevention and control of salinization. When there is a flushing requirement in salinized areas, the flushing drainage flow should be used as the verification flow. 2 In areas where waterlogging, waterlogging and salinization coexist, the drainage flow for drainage, waterlogging control and salinization prevention and control should be determined according to the design standards, and the design flow and verification flow should be selected from them. 3 For the comprehensive utilization of drainage, diversion, storage and irrigation, the flow requirements of other utilization methods should also be considered under the condition of meeting the drainage design flow.
3.3.2 The depth and spacing of the final fixed ditch should be determined according to
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