ABSTRACT
Irrigation schemes across sub-Saharan Africa are constructed with the intention of increasing agricultural production to increase food security, reduce poverty and improve economic growth. However, most of these schemes are not performing as expected. This study therefore, diagnosed performance gaps in the pilot irrigation schemes of Mubuku and Doho in Uganda and analysed sustainable improvement options. Data was collected through systematic review of literature and scheme data, direct measurements at the schemes, field surveys, inspections, and key informant interviews. For each scheme, data for climate, irrigation, flow measurements, crop yields and farm gate prices were collected. Comparative indicators of agricultural output, water supply, financial and physical sustainability were used to assess scheme performance using standard approaches by International Water Management Institute (IWMI). The findings showed that the schemes were not performing optimally with crop yields being far below the attainable potential. The major contributing factors to the low performance were low water use efficiency and low agricultural output. Poor flow control, poor water distribution, and poor on-farm water application contributed to low water use efficiency. Low agricultural production was attributed to poor crop yields resulting from poor agronomic practices, poor irrigation scheduling and low produce prices. The financial self-sufficiency indicator pointed to farmers' inability to operate and maintain irrigation schemes effectively. Improving the irrigation schemes performance requires a multidisciplinary approach targeting the improvement water use efficiency and agricultural output.
ABSTRACT
Soil erosion and sedimentation contribute to deteriorating water quality, adverse alterations in basin hydrology and overall ecosystem biogeochemistry. Thus, understanding soil erosion patterns in catchments is critical for conservation planning. This study was conducted in a peri-urban Inner Murchison Bay (IMB) catchment on the northern shores of Lake Victoria since most soil erosion studies in Sub-Saharan Africa have been focused on rural landscapes. The study sought to identify sediment sources by mapping erosion hotspots using the revised universal soil loss equation (RUSLE) model in appendage with field walks. RUSLE model was built in ArcGIS 10.5 software with factors including: rainfall erosivity, soil erodibility, slope length and steepness, land cover and support practices. The model was run, producing an erosion risk map and field assessments conducted to ground-truth findings and identify other hotspots. The percentage areas for RUSLE modelled erosion rates were: 66.8% for 0-2 t ha-1 year-1; 10.8% for 2-5 t ha-1 year-1; 10.1% for 5-10 t ha-1 year-1; 9% for 10-50 t ha-1 year-1 and 3.3% for 50-100 t ha-1 year-1. Average erosion risk was 7 t ha-1 year-1 and the total watershed erosion risk was 197,400 t year-1, with croplands and steep areas (slope factor > 20) as the major hotspots (> 5 t ha-1 year-1). Field walks revealed exposed soils, marrum (gravel) roads and unlined drainage channels as other sediment sources. This study provided the first assessment of erosion risk in this peri-urban catchment, to serve as a basis for identifying mitigation priorities. It is recommended that tailored soil and water conservation measures be integrated into physical planning, focusing on identified non-conventional hotspots to ameliorate sediment pollution in Lake Victoria.
