Improving Water Reuse in Paddy Field Districts with Cascaded On-farm Ponds using Hydrologic Model Simulations

On-Farm Ponds (OFPs) are an important irrigation facility in rice-based irrigation systems. An OFP water reuse system in paddy field districts is composed of upstream commanded paddy fields, irrigation and drainage ditches, cascaded OFPs and downstream irrigated paddy fields. This study assesses the performance of an OFP water reuse system and explores potential water management strategies to enhance return flow reuse for rice production. A cascaded model including a modified two-tank module and a pond water balance module is developed to describe hydrologic characteristics of the water reuse system. Model calibration and validation show that the measured and simulated data are in a good agreement and the proposed model can be used to hydrologic analyses of OFP water reuse systems. The water reuse system has high water reuse efficiency as the return flow regulated by OFPs was reused several times from the upstream to downstream of the paddy fields. Return flow and actual reuse water increase with the maximum ponded depth of paddy fields. As the water level in a drainage ditch decreases, the available return flow increases and local water shortage can be alleviated. The supply-and-demand gap between seasons becomes more harmonized when the regulated water level in pond increases, resulting in a decrease in water shortage. The reuse of return flow is a quick-response water supply solution to meet the rice water demand during peak demand periods.