Land deals in western Ethiopia put the Grand Ethiopian Renaissance Dam at risk of siltation

Global land deals, also coined 'land grabbing', lead to transferring land (use) rights from local communities to (inter)national investors, and to dramatic shifts in agricultural systems. In the studied Benishangul-Gumuz region (Western Ethiopia) this concerns changes from shifting cultivation and slash-and-burn to permanent cultivation of cereals and export crops on large parcels. On the other hand, sustainable hydropower development necessitates conservation of upstream catchments as land degradation poses siltation threats to reservoirs. Ethiopia is constructing Africa's largest hydropower dam, the Grand Ethiopian Renaissance Dam Nordic Geographers Meeting, Stockholm 18th – 21st June 2017 7 (GERD), on the Blue Nile. Given the commercialization of large tracts of land in the closer catchments, there is a need to explore the effects on peak discharge and suspended sediment concentration (SSC). A field survey was conducted on 20 ephemeral streams to compare annual maximum peak discharges between catchments (0.4 – 15.5 km²), eight of which drain commercial farms and twelve others land under traditional management. We measured channel characteristics, observed flood marks and applied the empirical Manning equation to calculate peak discharges. SSC samples were taken during each runoff event from a stream in each of the two dominant land management categories. Results indicated that there is a 51% increase in the magnitude of peak runoff from commercial farms compared to traditionally managed lands. Catchments dominated by commercial farms also have a significantly higher SSC (mean = 6.44 ± 2.23 g l-1) compared to catchments without commercial farms (mean = 2.77 ± 2.31 g l-1). Forests and woodlands have a strong buffering effect; croplands are generating higher peak discharges and sediment transport. Leasing forests and woodland to agricultural companies has resulted in deforestation. Consequently, the increased runoff response may lead to downstream bank erosion, affects downstream communities, and the increased sediment transport poses a significant threat to the multi-billion dollars hydropower reservoir of the GERD.

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