Application of SWAT model in water resources assessment to guide irrigation development in Malaba sub catchment, Uganda.

Abstract

Human population increase, economic development, climate change and other drivers alter water resources availability and use resulting in increased risks of extreme low and high flows, drastically altered flow regimes; threats to water quality and water demands surpassing renewable supply. In this research, water resources assessment of river Malaba sub-catchment was carried out using SWAT model, Irrigation Water requirement of rice crop determined using the CROPWAT 8.0 software, border strip irrigation design carried out accompanied with a simulation of border strip irrigation hydraulics using WinSRFR 4, software and the suitable sites for location of valley tanks executed using: Multi criteria decision analysis in: GIS environment. A sensitivity analysis was done in SWATCUP using observed data for 497 simulations. The 10 most sensitive parameters were used for calibration and validation of the model in SWAT-CUP using SUFI-2 SWAT model performance was based on the R2 and NSI values of both calibration and validation. The R2 value of 0.93 and 0.90 for calibration and. validation respectively were obtained. The NSI of 0.90 and 0.89 for calibration and validation respectively were also obtained. The crop water requirements were determined using 15year climatic data using CROPWAT 8.0. A gross irrigation requirement (GIR) of 29.76mm obtained and IWR of each command area. A border strip irrigation system for the rice crop was designed and simulated using WinSRFR 4.1.3 software and an economical and hydraulically efficient trapezoidal channel was designed. Application efficiency of 5.9% and percentage runoff of 32% were generated from WinSRFR 4. 1.3. The suitable sites for location of valley tanks was done using a multi criteria decision analysis and pairwise comparison made for each criterion considered. These suitable sites were Kisoko, Ongere, Nawire, Nakwiga and Paya villages in Tororo district, Buyunda and Bugaiama in Busia district and Butema, Namukonge and Bugalama in Bugiri districts. Different blocks of irrigation command areas were delineated in arc GIS 10.1 using a multi criteria decision analysis and pailwise comparison made for each' criterion considered. The delineated command area blocks were 5 having a total area of 7,835 hectares 2 blocks can be irrigated by direct abstraction from river Malaba by gravity flow 3 blocks can be irrigated by using valley tanks.