| Abstract |
Isotopic and geochemical investigations have been carried out in order to identify the recharge area of the Tendaho geothermal field. Tendaho was one of the geothermal fields recommended for development by UNDP, (19730. The Awash Ricer, which is one of the largest rivers in the country flows from the highland to this large plain lowland area, Therefore, the Awash Ricer makes the area attractive for agricultural development mainly for irrigation of cotton, and the energy demand is growing strongly. It is believed that developing the geothermal resource can solve the energy problem and therefore four wells were drilled and a permeability problem was observed. To study the hydrology the area between longitudes N 8o36'30" and N11o10'00" and between longitudes E39o5'30" and E 41o17'30" which encompasses southern Afar, part of Northern Afar and the western Escarpment was selected. Deuterium 2H, 18O and geochemical investigation of the study area proved that there exists a regional underground flow, which starts from Lakes District and through the Southern Afar reaches the Tendaho graben, During this process waters evolve towards "mature" water dominated by chloride ions. Similarly the large 18O shift in the Tendaho waters indicates that they have undergone more water rock interaction process that the more recent waters in the Lakes District. From isotopic study it was also possible to observe that the Mojo-NazrethWelenchiti are (south of Southern Afar) might be the source of recharge to the Tendaho geothermal field. Strong oxygen 18 shift was observed in the deep wells drilled in the Tendaho geothermal field. All hot and cold springs as well as the deep geothermal wells sampled during this survey discharge waters near neutral to mildly alkaline pH, with the exception of some which are highly alkaline. Three water types are identified namely, Na-K-CI, Na-K-HCO3 and NaK-SO4. |