A detailed water budget assessment of surface and subsurface water and its environments of Wama Catchments, East Wollega zone of Oromia region, Western Ethiopia.

This study aims to evaluate the environmental contamination assessment of surface and subsurface water characteristic of the Wama catchment based on hydro meteorological and hydro geochemical data analysis. The study area is located in southern parts of Abay river basin, Upper part of Didessa sub basin, and bounded between 8⁰24’0”N-9⁰0’0”N latitude and 36⁰24’0”E- 37⁰24’0”E longitude. It is characterized by highly rugged topography, dendritic drainage pattern, and tropical to sub-tropical climate condition.

Assessment of surface and groundwater of the catchment is studied based on conventional techniques, by gathering and interpreting hydro meteorological and hydro geochemical data. from long term mean monthly rainfall data, annual precipitation of the catchment is calculated as 1715 mm/ year. The PET value obtained by Penman method is estimated to be1059.1 mm/yr and used in the calculation of AET by Soil water balance. Potential evapotranspiration (PET) is estimated by using two approaches namely, Thornthwaite and Penman combination methods. Those methods gave 864.7 mm/yr and 1059.1mm/yr respectively. Thornthwaite method underestimates the value most probably because it relies on mean monthly temperature and sunshine hour.The groundwater recharge estimated from water balance method and chloride mass balance method were 481mm/year and 204mm/year respectively. The Actual Evapotranspiration (AET) was calculated using Turc method and Soil water balance method. The AET values obtained from these methods is found to be 717mm/year and 860mm/year respectively. During study the annual mean rainfall calculated by Arithmetic is 1453mm.

The study has computed evapotranspiration using Turc method and obtained 944.6mm/yr. The annual groundwater recharge estimated by applying both base flow separation and water balance technique was 196.6mm and 297.5mm respectively. Many borehole drilled around dam site with maximum depth of 92m revealed that fresh fractured and weathered trachyte basalt dominate the investigated area The fractured and weathered volcanic rocks are the main water bearing unit in the catchment. From the existing borehole data, the higher values of discharge, hydraulic conductivity and transmissivity zones are mapped at or near fractured regions.