GIS-Based surface irrigation potential assessment of Weyib river sub-basin

Abstract

The assessment of the surface irrigation potential process has the integration of information concerning the suitability of the land; water resource availability and climate variation are required in the water requirements of irrigated areas. Ethiopia has huge potential in expanding irrigation using available water resources. But, the country depended on rain-fed agriculture with limited use of irrigation for agricultural production. The major problem associated with rainfall-dependent agriculture in the country is the high degree of rainfall variability and unreliability. However, due to a lack of information related to cultivable and irrigation suitability of the land, its agricultural system does not yet fully productive. A geographic Information System (GIS) can be an effective tool in identifying irrigable land and mapping suitable land for irrigation. Therefore, the objective of this study was to assess the surface irrigation potential of the Weyib river watershed using ArcGIS 10.4.1. The main suitability factors, which were used to identify the potentially irrigable land for surface irrigation, were slope, soil characteristic, land use land cover, and distance from the water source. Irrigation suitability of each physical land parameter is classified based on the FAO guideline for land evaluation into four classes such as S1 (highly suitable), S2 (moderately suitable), S3 (marginally suitable), and N (not suitable) suitability classes, where the final potentially irrigable land was identified by weighting the factors of suitability. Irrigation water requirements of selected crops commonly grown in the area (Wheat, Barley, potato, and Cabbage) were computed from climate, crop, and soil data inputs using CropWat8.0 software, and the volume of minimum flow (90% exceedance flow of Weyib River) were estimated. By weighting values of the seven factors using the Analytic Hierarchy Process and overlaying by weighted overlay in ArcGIS 10.4.1, the irrigation suitability map was developed and the total suitable land for surface irrigation was found to be 427,671.55 ha (99.27 %) of the total area of the watershed was found in a range of highly suitable to marginally suitable whereas about 0.73% of the land was limited for irrigation developments. The river's capacity was insufficient for the irrigation application of the command area, as determined by a comparison between the amount of water needed and the river's monthly flow. Thus, any future planning for surface irrigation may include building a storage reservoir across the river to hold runoff during the rainy season.