Geology (Economic Geology, Geophysics): GLG 511

Geology (Economic Geology, Geophysics): GLG 511, BSc (Hons) examination June 2011

Geology (Mining and Exploration Geology, Mineralogy, Petrology): GLG 512

Geology (Mining and Exploration Geology, Mineralogy, Petrology): GLG 512, degree exmianation June 2011

Applicability of a Spatially Semi-Distributed Hydrological Model for Watershed Scale Runoff Estimation in Northwest Ethiopia

Estimation of runoff is vital forplanning activities in relation to integrated watershed management and flood protection measures. This research was conducted at one of the catchments in Abbay River (upper Blue Nile River) basin to assess the applicabilityof the Hydrologic Engineering Centre Hydrological Modelling Software (HEC-HMS) modelfor simulation of runoff. It was aimed at selecting the best loss and transform methods in the model, as well as testing the applicability of the calibrated model to ungauged watersheds. Two loss methods such as soil conservation service (SCS) and initial and constant methods with two transform methods including SCS and Clark unit hydrographs were considered in the study for selecting the best combinations applicable in the area. While comparing the simulation results of each combination, better results were obtained in the model set containing the initial and constant loss method and SCS unit hydrograph with a Nash-Sutcliff Efficiency (NSE) of 82.8%, R2 of 0.83, and 10.71% of relative bias errors, followed by initial and constant with Clarks unit hydrograph, and it can be used for similar ungauged watersheds

Groundwater recharge in the Akaki catchment, central Ethiopia: Evidence from environmental isotopes (delta18O, delta2H and delta3H) and chloride mass balance.

Recharge patterns, possible flow paths and the relative age of groundwater in the Akaki catchment in central Ethiopia have been investigated using stable environmental isotopes 18O and 2H and radioactive tritium (3H) coupled with conservative chloride measurements. Stable isotopic signatures are encoded in the groundwater solely from summer rainfall. Thus, groundwater recharge occurs predominantly in the summer months from late June to early September during the major Ethiopian rainy season. Winter recharge is lost through high evaporation-evapotranspiration within the unsaturated zone after relatively long dry periods of high accumulated soil moisture deficits. Chloride mass balance coupled with the isotope results demonstrates the presence of both preferential and piston flow groundwater recharge mechanisms. The stable and radioactive isotope measurements further revealed that groundwater in the Akaki catchment is found to be compartmentalized into zones. Groundwater mixing following the flow paths and topography is complicated by the lithologic complexity. An uncommon, highly depleted stable isotope and zero-3H groundwater, observed in a nearly east-west stretch through the central sector of the catchment, is coincident with the Filwoha Fault zone. Here, deep circulating meteoric water has lost its isotopic content through exchange reactions with CO2 originating at deeper sources or it has been recharged with precipitation from a different rainfall regime with a depleted isotopic content