The Role of Structures and Geomorphology On The Occurrenceof Groundwater In The Northern Main Ethiopian Rift System

Abstract

The Northern Main Ethiopian Rift system is known by its active geological and tectonicprocesses. This study used integrated field survey, RS and GIS, geological, structural,geomorphological, hydrogeological and hydrogeochemical methods to analyze the roleof geological structures and geomorphology for the occurrence of groundwater inNorthern Main Ethiopian Rift system. The Hydrogeology of the area is characterized bycomplex bimodal composition of geology and geological structures of NE-SW borderfaults and NNE-SSEW WFB, E-W trending transverse fault system, calderas, siliciccenters and spatter cones along the Rift floor.The highly productive aquifer is observed in the Akaki and Adaa plain with the yield(50-60L/S) and Mojo well field (15-30L/S). This is influenced by YTVL that cross-cut theNMER structure formed both shallow and deep aquifer system and due to local andregional recharge and high rainfall from the plateau sector. The Wonji basin is yieldingup to 10L/S from shallow aquifer system of alluvial deposits recharged from Kokareservoir and Awash River flow. Whereas, in Kereyu, and Wolenchiti basin, the yield isvery low to be 1.5L/S and in Lake Beseka region from 3 to 12L/S due to deep circulatedregional aquifer system from Plateau and adjacent escarpment and low local rechargeand recharge from Fantale and Abadir farm to Beseka lake. In the rift axis, due to theintense structures and deep sub surface circulation thermal springs and steams areemerged in Sodere, Geregedi and Boku thermal spring.The Eastern Plain of Dera and Iteya have a yield between 3 to 5 L/S associated to deepseated fault system that makes groundwater flow along the rift sector to undergo a deepcirculation except in Gonde and Huruta high discharge springs that are associated withlocal aquifer. The hydrogeochemical data shows that Ca-Mg-HCO3 of shallow freshgroundwater to NaHCO3 and high TDS (>2,000 mg/l) and EC (>3,000ms/m) highlydeeply evolved and undergone strong water-rock interaction in the subsurface andintermixing of waters in the Beseka lake region.