ASSESSMENT OF GROUNDWATER POTENTIAL AND ITS QUALITY FOR IRRIGATION PURPOSE IN SUB CATCHMENT OF BORKENA RIVER, KOMBOLCHA, ETHIOPIA

Abstract

Even though productivity and quality of groundwater is quite high as compared to surface water, groundwater resources have not yet been properly exploited in Ethiopia. This study attempts to assess the potential and quality of groundwater for irrigation in sub catchment of Borkena river, Kombolcha Woreda, South Wollo. GIS and Remote sensing techniques were used for the study. Thematic maps like land use land cover, rainfall, geomorphology, geology, slope, soil, drainage density and lineament density map were prepared. All the thematic layer maps were converted in to raster format. For the various thematic map units weight factors were decided based on relative contribution of each map towards groundwater potential, finally all layers were overplayed and ground water potential zones were delineated. For water quality analysis, samples from 8 dug wells and 15 tube wells were collected and chemically analyzed in laboratory for major ions Electrical conductivity, pH and temperature were measured in in-situ. SAR, SSP, RSC, and MH were calculated for each sample and matched against the WHO standard. The result of groundwater potential assessment shows 0.6% (1.6 km2) of the study area was classified as Very Good; 15% (40.08 km2) of the area as Good; 21% (55.6 km2) as moderate; 33% (87.22 km2) as Poor, and the rest 30.4% (80.7 km2) as Very Poor potentials for ground water exploitation. Moreover, the southern portion of the study area, where kombolcha is located falls on moderate groundwater potential zone. For water quality analysis the areal groundwater can be used for irrigation as per SAR, SSP and RSC criteria. However, according to MH criteria, 73.91% of the samples in October, 47.83% in January and 26.09% in July were found not suitable for irrigation purpose. It is possible to conclude that large proportion of the areal groundwater was found to have inadequate potential but suitable quality so effective utilization with proper management techniques should be used in order to use it for irrigation.