Experimental and modeling evaluation of siphon-type subsurface drainage performance in flooding and waterlogging removal.

Agricultural subsurface drainage is necessary for crop production in humid, poorly drained regions with frequent rainfall. Flooding and waterlogging have become more widespread and frequent in recent years, and effective measures should be adopted to increase the subsurface drainage capacity and alleviate flooding and waterlogging disasters after short-term heavy rainfall. However, subsurface drainage focused on the layout parameters (drain depth, drain spacing, etc.) in previous studies, and these measures were limited and cumbersome in the improvement of the flow rate of subsurface drainage. Thus, we aimed to alleviate the flooding and waterlogging threats to farmland and innovatively proposed a new method to increase the flow rate of subsurface drainage, namely siphon-type subsurface drainage. The paper evaluated the performance of the siphon-type subsurface drainage by the indoor sand tank test and the HYDRUS-2D model. Three factors were considered during the experiments: conventional and improved subsurface drainage; shallow, medium, and deep drain depth; and the outlet elevation, including the outlet elevation of the drain pipe under the non-siphon drainage and the outlet elevation of the siphon pipe under the siphon drainage. The results indicated that the siphon-type subsurface drainage performed better under the conditions of steady-state ponding and ponding subsided. The flow rate of the siphon-type subsurface drainage was 27.1–45.7%, 41.8–89.8%, and 39.3–50.5% higher than that of conventional, thin-improved, and thick-improved subsurface drainage with non-siphon drainage under steady-state ponding, respectively. It also had a significant advantage when the outlet elevation was the same. The siphon-type subsurface drainage could increase the flow rate during ponding subsided and reduce the flow rate attenuation degree before the ponding disappears. The flooding removal effect of the siphon-type subsurface drainage was significantly better than that of non-siphon subsurface drainage. The water head and flow rate were used to calibrate and validate the HYDRUS-2D model. The results indicated that the simulated values of flow rate matched well with the measured ones and the relative errors were less than 10%. The influence range and absolute values of the negative water head increased with the decrease of outlet elevation, and the increase effect of flow rate increased with the decrease of the water head. The siphon-type subsurface drainage has more control distance than the non-siphon. The advantages of siphon-type subsurface drainage are not only prominent in quart sand but also applicable to field soil. The results of this study could provide technical support for the application of flooding and waterlogging removal in areas where waterlogging is prone to occur and could improve the ability of agricultural production to address waterlogging disasters. • A siphon-type subsurface drainage to improve the subsurface drainage capacity is proposed. • The drainage rule of the siphon-type subsurface drainage is studied. • Effect of flooding and waterlogging removal of siphon-type subsurface drainage is revealed. • The flow rate attenuation degree of a siphon is assessed. • The performance of siphon-type subsurface drainage is validated by HYDRUS-2D model. [ABSTRACT FROM AUTHOR]