Improving Irrigation Water Use and Management in Large Paddy Rice Fields Using SWAT Model
Abstract
Paddy fields are designed with water impoundments in which their ecohydrological processes are affected by water management practices, the case in the Doho rice scheme, Butaleja District, Uganda, with large paddy fields and farmers facing water management challenges. The water source for this Ugandan scheme originates from Manafwa River, which experiences floods due to climate change, poor drainage, and land use change, affecting paddy production. Flooding deposits silt in the channels. The Soil and Water Assessment Tool (SWAT) simulates and simplifies hydrological processes in large paddy fields. The SWAT Model was used in this study to assess irrigation water use and sustainable water management strategies by simulating hydrologic processes within the catchment for a period of 35 years (2015 to 2050) using hydrological data from the Manafwa catchment and assessing future water-use demand. The SWAT output viewer was also applied to analyse water-use scenarios in the catchment. Model calibrations by SWAT-CUP were performed using the data from 2002 to 2008 and then validated with data from 2009 to 2013. The calibration was successfully performed in the SWAT model with Nash-Sutcliffe Efficiency (NSE) of 0.77 and a coefficient of determination (R2) of 0.79. On the other hand, NSE and R2 values for validation were 0.55 and 0.7 respectively. Calibration data was used to check model performance, which produced reliable results. Average annual available water in the Manafwa River was 949.5192 m3/s and the crop water requirement of the paddy rice in the Doho rice scheme was 11.053 M Similarly, the SWAT output viewer showed that the pothole impoundment module improved irrigation water in times of competitive demands and dry seasons. Therefore, implementing desiltation and grassed waterways minimizes soil erosion, a reliable approach for reducing sedimentation in the river and the channels, significantly contributing to water management in such large irrigation schemes.
