Drainage-Process Analyses for Agricultural Non-Point-Source Pollution from Irrigated Paddy Systems

Abstract

The aim of this study was to investigate the effects of drainage processes on non-point-source pollution in a complex irrigation and drainage system. Field experiments were conducted to measure quality and quantity of leakage and irrigation-return water in field drains, lateral drains, and the main drain during paddy-growing periods for 2 years. Water-flow and chemical-transport processes from paddy fields to field drains were simulated numerically. A modified Muskingum method was proposed to calculate the processes of water flow and chemical transport in lateral and main drains. Results showed that the Muskingum method was applied successfully to calculate the drainage and chemical-transport processes, as well as to quantify the effect of drain storage on the processes. Results from the field experiments and simulations indicated that the fate of ammonium (