Water balance in Aba’ala marginal graben along the western margin of Northern Ethiopia

Closed basins are major development corridors in the semi-arid mountain catchments of Ethiopia. But despite the growing natural and anthropogenic pressures on water resources, there is still inadequate knowledge on hydrological behaviour of marginal grabens to develop sustainable management strategies. The objective of this study is to quantify the components of water balance in the Aba’ala graben. Therefore, rain gauges, pressure transducers, and staff gauges were installed at representative rivers. Monthly based transect studies across the runoff production areas were undertaken to understand the runoff mechanisms. We developed rating curves and hydrographs for each gauging station to analyse the discharges, we estimated actual evapotranspiration and we used the model parameters of gauged catchments to estimate the runoff inflow from ungauged catchments. This study shows that rainfall has an erratic behavior in the marginal graben, which led to enormous runoff volumes. The largest share of the discharges was generated from western escarpments and took place in the form of flash floods, mainly between July and August. Hydrograph analysis reveals that there were a series of quickflows and baseflows in the rainy season. Travertine dams situated in the upper catchment of Murga and Aba’ala Rivers were the production area of many springs that recharged the flat productive area. However, there is a massive risk of water loss through deep percolation and evapotranspiration. Much of the flash floods and regular floods left the marginal graben bottom via its single outlet. These flash floods could be potentially intercepted by selective tree species, terraces and check dams to improve blue and green water storages in the Aba’ala marginal graben. A better understanding of the hydrological behaviour of the marginal graben is proven valuable towards a sustainable land management in the closed basins.