Evaluation of Drainage Water Detention Efficiency of Off-Line Ditch-Pond Systems and Its Influencing Factors

Abstract

Ditch-pond systems can effectively alleviate the adverse effects of agricultural drainage on downstream canals and flood control in downstream areas. In this study, peak flow reduction rate (PFR) and drainage volume detention rate (DVD) are used to evaluate the effectiveness of an off-line ditch-pond system for reducing peak flow, retarding agricultural drainage water, and examining the key influencing factors. The results show that the PFR and DVD of the off-line ditch-pond system are significantly affected by three parameters: weir depth (Ld), weir width (Lw), and pond area-to-drainage area ratio (Ksp). Both the PFR and DVD increase with the increase in Ld, Lw, and Ksp. The effects of Ld and Lw on the PFR and the DVD are significant, whereas that Ksp is relatively small. Adjusting Ld and Lw increases both the PFR and DVD up to 80%. Specifically, Ld contributes 75% of the variations in the PFR and the DVD, and Lw affects only 17% of the PFR variations and 11% of the DVD variations. These findings confirm that an off-line ditch-pond system can be effectively used for the detention of agricultural drainage water. Thus, when such a system is designed with an appropriate diversion weir, the impact of agricultural drainage water on downstream canals and downstream areas can be reduced remarkably.