GIS-BASED SURFACE IRRIGATION POTENTIAL ASSSESSMENT OF DIRMA WATERSHED, DEMBIA WEREDA, NORTH GONDER ZONE, ETHIOPIA

Abstract

This study was under taken to evaluate suitability of Dirma watershed for surface irrigation potential. The methodology included evaluation of slope, major soil physical properties and surface water resources availability of the watershed. Suitability of the area with respect to slope, soil and surface water resources availability were evaluated using Arc GIS 10.1. In the weighted overlay analysis, high weight was given to slope, since it is the determinant factor for surface irrigation development. Potentially suitable sites for surface irrigation development were evaluated for selected vegetable crops, Potato and Tomato. The reference evapotranspiration and net effective rainfall for each of the climatic station (Gorgora and Gonder) and net and gross irrigation requirement for each of the crop for each of the climatic station was estimated using CROPWAT software. The minimum water requirement of Tomato was found to be equal to 0.07 m 3 /s/ha in April during the development stage at Gonder meteorological station and 0.07 m 3 /s/ha in January at initial stage at Gorgora station. The maximum water equal to 0.15 m 3 /s/ha for tomato crop was required in March at Gonder and 0.15 m 3 /s/ha in May at Gorgora station. In case of Potato crop, minimum water equal to 0.19 m 3 /s/ha was required in January at Gorgora and 0.157 m 3 /s/ha at Gonder at initial stage. However, the maximum water equal to 0.38 m 3 /s/ha was required in March at Gorgora and 0.257 m 3 /s/ha at Gonder in mid stage. The total value of the gross water requirement for both the crops for both the climatic stations varied from 0.17 m 3 /s to 0.93m 3 /s. The water available from Dirma River during Jan, April and May was more than the gross irrigation water requirement. However, the water available during Feb and March was less than the requirement. Result of the suitability model revealed that about 68.3% (300.93 km 2 ) of the total watershed area (440.6 km 2 ) was in the range of highly to marginally suitable for surface irrigation development with respect the suitability of slope, soil and water resource availability factors.