Small-scale irrigation expansion along the dam-regulated Tekeze River in Northern Ethiopia

Impact of Hydropower Dam Operation and Management on Downstream Hydrogeomorphology in Semi-Arid Environments (Tekeze, Northern Ethiopia)

“…River bed degradation consequently could have led to an underestimation of actual discharges, and could be responsible for the observed decreasing trend in runoff volume downstream of the dam between 2010 and 2015 (Figure 5). During this period, no corresponding declining trend in reservoir inflow was observed-the inter-annual rainfall variability is expected to be similar as in the upstream catchment-and the extracted amount of water between the two stations is estimated to have remained invariable, as irrigated agriculture is absent along this stretch of the river [26]. In addition to river bed degradation, localized river bed aggradation also was observed in the first 150 RKs downstream of the dam.…”

“…Third, the field interviews also greatly helped us to interpret the post-dam hydrogeomorphic system as local inhabitants have indicated the timing and order of magnitude of different changes and helped to better understand alterations in riparian vegetation. While studying downstream hydrogeomorphic dynamics, it moreover remains important to also consider dam-induced social impacts, which can only be understood properly by interviewing riparian water users [26].…”

“…Third, dam-induced reduced high flows and increased low flows have also caused humans to increasingly occupy floodplains for irrigated agriculture. Since the Tekeze Dam became operational, the irrigated area along the river has expanded from 433 ha to 1698 ha, mainly consisting of fruit plantations, and even the lower river terraces have become cultivated [26]. Similarly to natural vegetation expansion, fruit trees reduce flow velocity during floods, what leads to sediment trapping and temporary runoff storage.…”

“…A total of 179 ha of farmland was reported damaged to the local agricultural specialists. This corresponds to 11% of the total irrigated area along the Tekeze River [26]. While most plants were damaged by high water levels, muddy depositions on banana leaves also caused numerous plants to die, as photosynthesis was hindered.…”

“…In (semi)-arid environments, it is especially important to properly assess dam-induced downstream impacts as dam-regulated rivers become very attractive for human settlers. Floodplains increasingly become occupied for irrigated agriculture and consequently, people increasingly depend on the newly obtained water conditions for their livelihood [25,26]. With this study, we aim to improve the understanding of hydrogeomorphic impacts induced by hydropower dams in (semi-)arid environments with high inter-annual rainfall variability, operated under normal circumstances and in case of extreme high water levels.…”