Impact of rift tectonics on the groundwater system of Awash Basin in the East African Rift - multidisciplinary characterization using isotope hydrology , remote sensing and hydrochemistry
Final Report Abstract
In the semi-arid, tectonically active Main Ethiopian Rift (MER) a growing population is resulting in increased use of ground- and surface -water for drinking and irrigation purposes. This study focuses on the groundwater system in the upper Awash basin of the MER. With a combination of isotope hydrology, hydrochemistry and remote sensing we investigated the origin, dynamics, and flow paths of the groundwater system and how it is affected by the tectonic setting of the Rift. The occurrence of recharge on the Ethiopian plateau is well known in contrast to the escarpment and the Rift valley. Using isotope methods (18O, 2H, 3H) we could show that there is also active groundwater recharge on the western as well as on the eastern escarpment down to an elevation of 1950 m a.s.l. Below this altitude we did not find evidence of active groundwater recharge. Groundwater ages of 1000 to 5000 years in the Rift valley indicate that there is no significant recent recharge in the semi-arid Rift valley. As one major result the new data allowed us to refine the conceptual model of groundwater flow from the Ethiopian highlands bordering the Rift valley into the semi-arid part ofthe MER. The distribution of groundwater ages in the Rift valley suggests that groundwater flow in the Main Ethiopian Rift is more complex than suggested so far. Apparently groundwater from recharge on the plateau not only enters the Rift along the direction of the Awash river, but also along the complete western and eastern escarpment edges. Surface watergroundwater-interaction is thought to be the driving force behind the rapid increase in lake level of Lake Beseka in the northern part of the study area. Our results suggest that the extension of the lake originates from an increased discharge of the cold and hot springs in the western part of the lake. The growth of Lake Beseka also leads to surface water infiltration in the eastern part and hence affects the groundwater located down-gradient the lake. Already the lake's signature can clearly be seen in groundwater beneath the Metehara Sugar Plantation, which is located 6 to 8 km east ofthe lake. The knowledge on recharge has to be complemented by further detailed soil and vadose zone water investigations at relevant locations along the escarpment and the Rift valley in a next step. Concurrently, more distributed investigation techniques like e.g. geophysics on the field scale or remote sensing on the catchment scale have to be added in order to draw conclusions on the spatial variation of recharge beyond the plot scale. We are currently modelling the groundwater recharge of the Upper Awash region in the Main Ethiopian Rift using remote sensing data exclusively, in any cases where that is possible. All these data will be implemented in a spatially distributed hydro(geo)logical and groundwater flow model coupled with a simple stochastic discrete fracture (SDF) model in order to study the role of faults and fractures in the flow of groundwater. The outcome of this project is to allow a lowcost, precise, large scale, 3D flow model in arid regions characterized by strong tectonic influence with very variable climatic conditions and poor logistic accessibility. The outcome can hence be used for an analysis of water availability and water use which is fundamental for the implementation and maintenance of a sustainable water resources management in the Main Ethiopian Rift.
Publications
- (2007) Applying remote sensing techniques and isotope hydrology in the investigation of the impact of fault and fracture zones on groundwater flow in the East African Rift of Ethiopia. - Jahrestagung Afrikagruppe deutscher Geowissenschaftler 2007, Potsdam 6.-7. 07.2007
S. Stadler, K. Adem, K. Osenbrück, R. Gloaguen
- (2007) Isotopes as a marker for potential impact of rift tectonics on the groundwater system of the Awash Basin in the East African Rift. - 7th International Symposium on Applied Isotope Geochemistry. Stellenbosch, SA, 10-14 Sept. 2007
S. Stadler, K. Adem, K. Osenbrück, R. Gloaguen
- (2008) Combining 18O, 2H, 3H, 88Sr/87Sr and remote sensing for identifying the impact of tectonics on groundwater flow in the East African Rift of Ethiopia. - FH-DGG 2008, 21.-24.05.2008; Göttingen
S. Stadler, K. Osenbrück, R. Gloaguen
- (2009) Gully erosion mapping using ASTER data and drainage network analysis in the Main Ethiopian Rift. In Geoscience and Remote Sensing Symposium, 2009. IGARSS 2009. IEEE International, 13-17 July 2009
M. Bouaziz, A. Wijaya and R. Gloaguen
- (2009) Macro-scale hydrological modelling in arid environments based on remote sensing data: a case study in Ethiopia. In Geoscience and Remote Sensing Symposium, 2009. IGARSS 2009. IEEE International, 13-17 July 2009
M. Knoche , R. Gloaguen and T. Rödiger
- (2009) Non-climatic growth of the saline Lake Beseka, Main Ethiopian Rift. J. Arid Environments 73(3), 287-295
A. Goerner, E. Jolie, R. Gloaguen
- (2009) Remote Sensing Based Water Balance Estimation in the Main Ethiopian Rift Valley. In Geoscience and Remote Sensing Symposium, 2009. IGARSS 2009. IEEE International, 13-17 July 2009
S. Haas, R. Gloaguen
- (2009) Surface watergroundwater interaction in the Lake Beseka area, Main Ethiopian Rift, investigated by a multi-isotope approach. 8th International Symposium on Applied Isotope Geochemistry, Montreal, Sept. 2009
A. Bretzler, K. Osenbrück, K. Knöller, R. Gloaguen, S. Stadler
