Assessment of groundwater suitability for irrigation in three sub catchments in Upper Athi River Basin, Kenya

Over the years, erratic rainfall pattern coupled with increasing population has led to the reliance on groundwater as an alternative and sustainable source for crop irrigation to meet increasing food demand. Irrigation of crops though essential, if not done with care through good practices and use of quality water can lead to soil salinization and ecological unsustainability. This study was carried out to assess the salinity of groundwater used for irrigation in three sub catchments in the Upper Athi River Basin of Kenya. Stratified random sampling technique was used to select representative boreholes and shallow wells for the study. In all, water from 17 boreholes and 17 shallow wells spread across the study area were sampled and analysed for selected physico-chemical properties. Standard methods were used for all the laboratory analysis; temperature, pH and electrical conductivity (EC) of water samples were measured in the field. The results obtained were compared with FAO Water Quality Guidelines for Irrigation. pH ranged from 4.2 to 7.13 indicating weak acidity with about 75% samples falling below lower guideline value. EC values ranged from 467 to 1328 μS/cm which were within FAO and NEMA permissible limits for irrigation purposes. All salts ions were within permissible irrigation water suitability standards except CO3-, Cl and K+. 97% samples had above the recommended carbonate concentrations while 80% had more potassium than the recommended value with the remaining 20% being boreholes. In relation to chloride concentrations, samples from shallow wells are not suitable for sprinkler irrigation since they were above the recommended levels; however, 58% were suitable for surface irrigation. For the boreholes, chloride concentrations were suitable for both surface and sprinkler irrigation. In conclusion, the boreholes had less ions as compared to shallow wells. This research may serve as a preliminary study to provide baseline information that may direct future water quality assessment studies in the study area. Key words: Irrigation, groundwater quality, boreholes, shallow wells, physico-chemical quality, salinity, sodicity.