Groundwater potential analysis for microscale irrigation in Isingiro District

Abstract

Rainfall variability and recurrent drought constrain rain-fed coffee production and water security in Isingiro District, creating a need for spatially targeted groundwater development for microscale irrigation. The thesis assessed groundwater potential, quantified irrigation and domestic water demand, and developed a groundwater suitability map for sustainable microscale irrigation planning. Isingiro District, in southwestern Uganda, is characterized by a semi-arid climate, undulating terrain, Precambrian basement complex geology, and predominantly agricultural land use. Geographic Information Systems, Remote Sensing, ArcGIS, Multi-Criteria Decision Analysis, the Analytic Hierarchy Process, and Weighted Overlay Analysis were used to integrate seven hydrogeological and environmental factors at 30 m resolution, while CROPWAT and the FAO Penman–Monteith method were applied to estimate coffee water requirements. The suitability map combined groundwater potential, irrigation demand, soil suitability, infrastructure accessibility and slope was validated using 22 borehole yields from different sites. Ground water potential mapping showed that low, moderate, high and very high potential zones covered 44.7%, 30.9%, 14% and 6% of the district respectively and very low potential occupied 4.5%. Annual coffee evapotranspiration was 1241.6mm, effective rainfall was 904.6mm, and the net irrigation requirement was 377mm, with irrigation required during 8months and peak deficits of 69.8mm in January and 56.8mm in July. The current domestic and livestock water demand was 9.478Mm3/year of which the livestock accounted for 51.4%, while the population was projected to reach 1.64M by 2055. Moderate to high potential zones yielded 48.0Mm3/year, applying a 25% safe yield limit and reserving 2.92Mm3/year for domestic and livestock use left 9.10Mm3/year for irrigation sufficient for 915ha ie 1830 farms of 0.5ha. The model achieved a classification accuracy of 77% and R2=0.68 with a mean borehole yield of 3.92m3/hr in the high suitable zones to 0.98 m3/hr in the low suitable zones. The results show that regulated ground water development can support coffee irrigation, especially in Kabuyanda, Rugaaga and Kashumba while protecting domestic and supply and long-term sustainability of the aquifers.