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

Abstract

Due to renewed interest in hydropower dams in the face of climate change, it is important to assess dam operations and management in combination with downstream impacts on rivers in (semi-)arid environments. In this study, the impacts of the Tekeze hydropower dam on downstream hydrology and river morphology were investigated, including impacts under normal and extreme reservoir operation conditions. Field observations, in-depth interviews, repeat terrestrial photographs, multi-year high-resolution satellite images, daily reservoir water levels and data on hourly to daily energy production were collected and studied. The results show that high flows (Q5) have declined (with factor 5), low flows (Q95) have increased (with factor 27), seasonal flow patterns have smoothened, river beds have incised (up to 4 m) and locally aggraded near tributary confluences. The active river bed has narrowed by 31%, which was accelerated by the gradual emergence of Tamarix nilotica and fruit plantations. A new post-dam equilibrium had been reached until it was disrupted by the 2018 emergency release, caused by reservoir management and above-normal reservoir inflow, and causing extensive erosion and agricultural losses downstream. Increased floodplain occupation for irrigated agriculture consequently provides an additional argument for reservoir operation optimization to avoid future risks for riparian communities.

From runoff contributor to runoff absorber: Spate irrigation on exclosures in Tigray's semi‐arid environment (Ethiopia)

“…For instance, the 9.3 × 10 9 m 3 hydropower reservoir on the nearby Tekeze River almost yearly accumulates excess water during the rainy season and sometimes during spring rains, which requires release of large volumes of excess water in the rainy season. The released water often affects the downstream dwellers as it floods croplands and infrastructure (Annys et al, 2020).…”

“…The released water often affects the downstream dwellers as it floods croplands and infrastructure (Annys et al, 2020).…”

Semi-Rigid Erosion Control Techniques with Geotextiles Applied to Reservoir Margins in Hydroelectric Power Plants, Brazil

“…Due to interest in Hydroelectric Powerplants (HPPs) considering climate change, it is important to evaluate the operations and management of HPPs in combination with the impacts arising [11], such as erosive processes. The problems of the erosion process are the main environmental impacts on the operation stage of most of the reservoirs of Brazilian HPPs, reflected in the loss of agricultural, urban, and forest areas, in water quality, in the abrasion of electromechanical equipment, and in the volume's reduction and useful life of the reservoirs by silting.…”

Fluvial Geomorphology and River Management

“…Concerning humid continental climatic zone areas, the papers of Heasley et al [7], Zingaro et al [8], and Heritage and Entwistle [9] analyse the fluvial systems of the UK under different point of views, whereas those of Szabó et al [10] and Bihałowicz and Wierzbicki [11] address fluvial systems of central Europe in Hungary and Poland, respectively. The fluvial system in the humid tropical climate of Brazil was analysed by Marinho et al [12], and that in the arid climate of Northern Ethiopia by Annys et al [13]. Finally, the behaviour of sinuosity rivers in arid to humid climates of China was modelled by Xiao et al [14] and the morphological evolution of the river channel and its restoration in the Yongding River was proposed by Li et al [15].…”

“…Finally, the authors analysed the impact of this process on the building of a hydroelectric dam in the area, considering the extreme climatic events. The building of a dam which blocks the river flow was another question debated by Annys et al [13] that analysed the impact produced by a hydropower dam on river morphology and downstream hydrology as a consequence of climate changes under normal and extremely high water levels. The study area is located in the semi-arid environment of the Tekeze River of Northern Ethiopia.…”