PHYSICAL IRRIGATION POTENTIAL ASSESSMENT FOR SURFACE IRRICATION: A CASE STUDY IN CHEMOGA WATERSHED, UPPER BLUE NILE BASIN, ETHIOPIA

Abstract

Assessment of available land and water resources for irrigation is essential for planning their use, to utilize limited resources efficiently and for the sustainable production of crops and food security of the ever increasing people in developing countries like Ethiopia. The study was mainly focused on assessing the available land and water resources potential for surface irrigation of Chemoga Watershed. This was done by using Geographic Information System (GIS)-based Multi Criteria Evaluation (MCE) tools, a hydrological Soil and Water Assessment Tool (SWAT) model, and a Crop Water and Irrigation Requirements Program of FAO (CROPWAT) model. GIS was used to map the land suitable for surface irrigation based on slope, soil, land use /land cover, and river proximity. SWAT model was used to estimate the water availability, and CROPWAT model calculate the reference crop evapotranspiration, effective rainfall, net and gross irrigation water requirement of crops. Potentially suitable land for surface irrigation development was evaluated by selecting six crops (barley, wheat, bean, maize, onion, and potato). The result of the overall weighted analysis for these factors gave about 25462.08 ha (71.4 %) of the Watershed land considered as high to moderately suitable whereas 10427.53 ha (28.6 %) were not suitable for surface irrigation. The SWAT model was calibrated and validated from the available hydro metrological and spatial data. Model performance result showed in between the observed and simulated stream flow with coefficient of determination (R2) and Nash-Sutcliffe efficiency (ENS) values 0.86 and 0.7 for calibration, and 0.74 and 0.63 for validation, respectively and indicated a good performance of the model in simulating the hydrology. The annual average simulated stream flow was evaluated and 36.2 m 3 /s. The water demand required by the selected crops was 228.18m3 /s/ha. From the total available suitable land, only 12376.03 ha can be irrigating with the available water