LULSEGED TAMENE, PAUL L. G. VLEK, SOOJIN PARK
Seoul National University, Department of Geography, Shilim-dong, Kwanak - Gu, The Republic of Korea
The food security and other development endeavours of Ethiopia are highly threatened due to increasing rainfall variability and population growth. A growing population with a corresponding increase in the frequency of drought and famine forced the expansion of cultivation and grazing to steep slopes and fragile environments. This further accelerates the rate and processes of land degradation. One alternative approach for enhancing the food security of people in such a dryland environment is surface water harvesting. This scheme has been implemented in the Tigray administrative region of Ethiopia where significant achievements have been observed including a four to six fold increase in the annual yield of farmers as well as development of springs and wells behind reservoirs due to ground water recharge. However, these achievements are not sustainable as most of the reservoirs have lost more than 50% of their storage capacity within less than five years of service. Currently, most of the reservoirs are not providing the intended service due to accelerated siltation problems. This has brought a big economic implication and resulted in a change of government strategy from ``reservoirs to small ponds''. Despite the fact that soil erosion is a major land degradation process in the region, no scientific attempts have been made so far to investigate the dynamics of siltation processes and controlling factors. This paper demonstrates the need for and approaches to an integrated approach to understand the determinant factors of reservoir siltation by combining different data layers from remote sensing, field surveys and existing maps in a GIS-based modelling approach. Both the spatial dynamics of geomorphologic and anthropologic factors are analysed and their relative contributions to reservoir siltation investigated. Terrain and its derivatives, land use/cover, drainage network and surface lithology are used as proxies to investigate the spatial variability of sediment yield at a catchment scale. Our approach could be considered as a simple and fast way of prioritising hotspot areas of erosion for appropriate management interventions particularly targeted to ameliorate the major causative factors at their specific locations.
Keywords: Erosion, GIS, food security, modelling, Northern Ethiopia, siltation, Tigray