Assessment Of Land Suitability For Surface Irrigation And Optimal Allocation Of Water Resources In Modjo River Watershed (Upper Awsh River Basin In Ethiopia)

Abstract

Irrigation is the artificial process of applying controlled amounts of water to land to assist in production of crops. Assessment of potential irrigable land is essential for the development of irrigated agriculture. The impact of unwise use of land resource, absence of land utilization according to its potential suitability and improper distribution of available water resource in the river watershed are still a serious problem in the world including Ethiopia. The main objective of this study was, therefore, to assess surface irrigation potential and to develop water allocation scenario for Modjo river watershed. Land suitability for surface irrigation was identified by considering the irrigation suitability factors such as land use land cover, soil and slope using Arc GIS 10.7.1. The final result of the suitability analysis revealed that 68% (136,437 ha) of the land was suitable for surface irrigation and the reaming 32% (64,928 ha) of the land was not suitable for surface irrigation. Irrigation water requirement for five dominant crop was calculated using CropWat 8.0 model. The results shown that the total gross irrigation water requirements of Onion, Tomato, Cabbage, Maize and Pepper were estimated to be 992, 938, 1012.8, 718 and 746.8 mm. Water Evaluation and Planning model (WEAP) was configured for the Mojo catchment and four demand nodes were added and connected with water sources. The output of the model was analyzed which includes catchment water balance, stream flow, supply requirement and unmet demand for future demand scenarios. From long term mean monthly precipitation the catchment gets 1,964.67, 16.88, 1,372.77, 419.73 and 136.39MCM under annual rain fall, irrigation, evapotranspiration, surface runoff and recharge water estimated. Annual average stream flow was estimated 455.42, 419.51 and 444.05MCM under reference, increasing irrigation and population increase demand scenarios respectively at 2030. The demand has shown fast growth where the supply requirement including the losses was estimated as 10.92, 871.89 and 11.37MCM under reference, increasing irrigation and population increase demand scenarios respectively. Based on scenario analysis by 2030 the total annual unmet demand is estimated at 0.66, 847.32 and 29.19MCM under reference, increasing irrigation and population increase scenarios respectively. Based on the result of this research it has been recommended that suitable area, water supply and demand side management measures should be well implemented in an integrated manner.