EFFECT OF DRAINAGE WATER REUSE ON SUPPLEMENTARY IRRIGATION AND DRAINAGE REDUCTION

Drainage water reuse has the potential to supplement irrigation, reduce drainage, and alleviate the area source pollution caused by agricultural drainage. This study aimed to evaluate the effects of influencing factors of drainage water reuse on supplementary irrigation and drainage reduction rates. To evaluate the effects, a water balance model was constructed to describe the irrigation water requirement and drainage water storage of a pond. The irrigation water requirement was calculated using the Penman-Monteith equation and the crop coefficient method while considering field leakage and effective rainfall; the drainage water volume was calculated using the improved Soil Conservation Service (SCS) model. The model was applied to the rice planting area in the Zhanghe Reservoir Irrigation District. Simulation results show that the supplementary irrigation and drainage reduction rates are primarily affected by the ratio of irrigation to drainage areas (RID), the pond volume ratio (PV), and the initial storage ratio (PSi); interactions among the three parameters are also observed. The RID, PV, and PSi contribute approximately 4: 3: 1 to the average variations in the supplementary irrigation rate. The supplementary irrigation rate increases with the values of PV and PSi but decreases with the increases of RID. For the drainage reduction rate variation, the average contribution percentages of PV and RID are 70% and 10%, respectively. Increasing PV and RID or reducing PSi enhances the drainage reduction rate. Adjusting the combination of parameters PV and RID can simultaneously maximize the supplementary irrigation and drainage reduction rates.