Improving irrigation water use and management in large paddy rice field using swat model:

Abstract

Paddy fields are designed ponding systems whose hydrological processes are impacted by water management practices. This is similar case with large paddy fields in Doho rice scheme, Butaleja district, Uganda. The scheme water sources originate from Manafwa River Catchment in Uganda which have been constrained by floods due to the increasing land use changes affecting the rice growing activities. These contributes to silt deposition of the channels in Doho rice scheme. Soil and Water Assessment Tool (SWAT) simplifies hydrological processes in such large paddy fields. In this research SWAT Model was used to assess water management, hydrologic modelling, irrigation water uses and evaluate sustainable management strategies through simulation for period of 2015 to 2050 for future use demand. The hydrology of the catchment was studied using Soil and Water Assessment Tool (SWAT). SWAT model was calibrated by SWAT-CUP using data from 2002 to 2008 and then validated using data from 2009 to 2013. The model was successfully calibrated with Nash-Sutcliffe Efficiency (NSE) of 0.77 and the coefficient of determination (R2) 0.79 and for validation with NSE of 0.55 and 0.7 for the R2. The calibrated model was then used to check the performance of the model and the results showed it was reliable. This study also applied SWAT output viewer to analyse scenarios on water use in Manafwa river catchment. The pothole impoundment module was proved by SWAT output viewer to improve irrigation water in times of stiff competition and in dry seasons. The implementation of desiltation and grassed water ways seemed to reduce soil erosion and therefore proving as reliable approach to reduce sedimentation in the river and the channels. This can contribute to water management in the scheme.