GIS-BASED AVAILABLE SURFACE WATER AND SUITABLE LAND RESOURCES ASSESSMENT FOR IRRIGATION IN ZALA, GOFA ZONE, SOUTH ETHIOPIA REGION

Abstract

The fundamental and essential issues for a country's sustainable development is land and water resource development. It is vital to comprehend the quantity or the distribution in place and time through various studies in order to use land and water resources in the most efficient and effective manner. Hence, this study was carried out on the hydrological process and evaluate the physical the suitability of land for irrigation in the Zala watershed of the Omo gibe basin using the SWAT model which is integrated with GIS based multi criteria decision making of AHP. The processes included defining the boundaries of watersheds, determining what area could be used for irrigation, and estimating the amount of surface runoff for irrigation. In this study calibration and validation of simulated versus measured flows of Zenti river and estimation of surface water in the watershed were conducted after sensitivity of hydrologic parameters had been identified using SWAT-CUP model tool. The hydrological simulation performance evaluation using SWAT-CUP were achieved with the objective function of calibration (R2=0.76 and NS =0.61) and Validation (R2=0.69 and NS =0.74). This model evaluation was performed at monthly levels. The Food and Agricultural Organization's guidelines for land evaluation were used to classify irrigation suitability factors such as DEM, slope, soil characteristics like type, texture, depth, drainage, land use/cover and proximity to water source and road. The land was then classified into four suitability classes: highly suitable (S1), moderately suitable (S2), marginally suitable (S3), and not suitable (N), which were determined by individually weighting the suitability factors and finally weighted overlaid. Irrigation water requirement of five commonly grown major crops (Tomato, potato, Cabbage, maize, sorghum) were computed from climate, crop and soil data inputs using Crop Water Requirement (CropWat8.0) software. By weighing analysis of all parameters 99.3 % of the study area was found in a range highly suitable to that of marginally suitable whereas about 0.7 % was restricted for irrigation developments. The estimated total annual available surface runoff water is 111.56Mm3/yr can irrigate 20,931ha,26163.2ha,29652ha by surface, sprinkler, drip irrigation method respectively. Therefore, the findings of this study are crucial to planners, decision-makers, community, and NGOs in order to develop the land and water resource for irrigated agriculture that would enhance crop production and ensure food security.