note:
China's farmland drainage industry and drainage technology have gained a lot of successful experience and made great progress, but the development in different places is uneven. In the future, we should further strengthen the matching of drainage system, establish a complete field drainage network, control the groundwater level, improve the standard of waterlogging control, conscientiously do a good job in drainage test and scientific management of drainage system, transform low-yield fields and improve drainage efficiency.
Extended data:
In order to control the groundwater level, it is necessary to dig field drains with certain spacing and depth. In the case of a given drainage depth, to meet certain drainage requirements, the smaller the drainage ditch spacing, the faster the groundwater decline, and the greater the groundwater level decline in a certain period of time;
However, the greater the drainage ditch spacing, the slower the groundwater level decline, and the smaller the groundwater level decline value. In the allowed time, when the groundwater depth Δ h is required to be constant, the greater the drainage ditch spacing, the greater the drainage ditch depth. On the contrary, the smaller the depth and spacing of the drainage ditch (Figure 1). drainage
When the allowable groundwater depth Δ h of crops remains unchanged, the depth d of the final fixed drainage ditch can be expressed as: d =Δh+Δ h+s.
Where Δ h is the groundwater depth (m) required by crops; Δ h refers to the difference between the groundwater level at the center point between two ditches and the ditch water level when the groundwater level has dropped to Δ h, generally not less than 0.2 ~ 0.3ms is the water depth in the final fixed drainage ditch, generally 0.1~ 0.2 m. ..
In order to speed up the drainage of surface water in the site, the last fixed drainage ditch should also have a certain spacing. The spacing is related to the formation process of surface rainfall runoff, allowable flooding duration and farmland water storage capacity, and must be determined by experiments.
In the areas with shallow groundwater depth and good water quality in northern China, shaft pumping and drainage are often combined with well irrigation. In the process of shaft pumping and drainage, because the well draws a certain amount of water from the groundwater aquifer, the groundwater level near the well will continue to decrease with the discharge of water.
This decrease is partly due to the long-term pumping of wells and insufficient groundwater recharge, which consumes a part of groundwater reserves, resulting in a funnel of groundwater level decline inside and outside the pumping area, as shown by the solid line in Figure 2, which is called static water level decline;
The other part is caused by the head loss in the process of groundwater collection into the well, and the closer it is to the pumping well, the greater its value. The total water level drop formed in the process of pumping water from the well is called dynamic water level drop, as shown by the dotted line in Figure 2. Due to the pumping and drainage of wells, the buried depth of groundwater is effectively increased, and the evaporation of groundwater is reduced, thus preventing soil from returning to salt.
In the case of using vertical shaft for irrigation and drainage, the spacing between wells depends on the irrigation area that can be controlled by the water output of a single well on the one hand, and on the requirement of controlling the groundwater level by a single well on the other hand. In areas where vertical shafts are used for simple drainage, the spacing between wells is mainly determined by the requirement of controlling groundwater level.
Baidu Encyclopedia-Design of Building Standards in Central and South China-Atlas of Water Supply and Drainage
Baidu encyclopedia-drainage