Effect of Buried Depth and Exit Control of Subsurface Tile on Drainage and Groundwater Depth

Abstract

【Objective】 Subsurface tile is a conventional drainage technology to prevent groundwater table from exceeding critical depths and causing waterlogging and soil salinization. In this paper, the effect of buried depth and exit control of the tile on drainage and groundwater depth was examined through field experiment. 【Method】 The experiment was conducted in the Lixin Drainage Test Area in Bozhou City, Anhui province. The tile length was 200 m and the space between adjacent tiles was 30 m. The exit of each tile was connected to a well with its position either kept at a constant elevation (CWTR) or dynamically controlled (DWTR). Drainage from each tile was measured using an electronic water meter, and change in groundwater depth was measured from a borehole drilled in the middle of the tiles. Groundwater flow in the drainage system was simulated using the DRAINMOD model. 【Result】 Shallow-burying the tile and CWTR control of the tile exit had similar effect in controlling groundwater depth and reducing drainage. The DWTR and CWTR were both able to reduce the groundwater table dropping and drainage in the early and late crop growth stages. In the middle growth stage, the groundwater depth under DWTR was significantly lower than that under CWTR, and the daily drainage from the former was significantly higher than that from the latter. For the conventional tile layout, the average groundwater depth under DWTR in a wet year was 13.9 cm lower than that under CWTR, and the drainage of the former was 2.1 times as that of the latter. Changes in the elevation of the tile exit in DWTR altered groundwater flow, and it took 7 to 12 days, depending on the tile space, for groundwater flow to reach a new steady state. 【Conclusion】 Dynamic control of the elevation of the tile exit in subsurface drainage systems can be an effective means to regulate groundwater flow, preventing waterlogging during flood seasons and ensuring sufficient soil moisture during dry seasons.

Keywords

• controlled drainage
• shallow buried tile
• constant water table
• dynamic water table
• groundwater depth
• drainage volume