Sustainable Hydropower Dam Operation Considering Downstream Riverbank Stability

Damages to hydraulic structures and bridge crossings, as well as loss of property are often reported due to erosion and mass failure in banks along a river, which are known to be affected by the flow of water and ground conditions. Both hydrologic and hydraulic factors along the river usually determine these riverbank alterations. However, when a hydropower dam is located upstream in a river, the downstream flow conditions mainly depend on the dam's operation and the hydraulic factors near the site of interest can be significantly affected by the pattern of flow released from the reservoir. Hydropower dams are operated not only for generating electricity but also for multiple purposes such as controlling floods and drought, supplying water for drinking and irrigation purposes, offering a safe recreational environment, improving water quality, and minimizing the impact on the ecology of the river downstream. Consequently, different discharge patterns are applied to manage the flow to meet the regulations and goals, which generally result in fluctuations in water surface elevation (WSE) along the river and subsequent changes in the groundwater table (GWT) in the vicinity of the riverbanks. All of these factors are known to affect the stability of riverbanks. However, this important aspect has not typically received the necessary consideration when scheduling the operation of a hydropower dam. Therefore, this study selected riverbank locations downstream of a hydropower dam in the Roanoke River, NC and evaluated the bank stability under different flow conditions. The fluctuations of WSE under the typical operational modes of the hydropower dam and its discharge patterns were reviewed. Changes in WSE and GWT were investigated, and the riverbank stability was evaluated considering riverbanks’ transient flow conditions with its discharge patterns. As a result, the hydropower dam operational modes were not the most critical factors to the slope failure of the analyzed riverbanks, but instability was expected when multiple factors were considered simultaneously. It is concluded that the hydropower dam does not seem to create adverse conditions for the analyzed riverbanks. However, the analysis proposed here for determining the WSE fluctuations caused by the dam operation and their potential impact on riverbank stability, is recommended for ensuring sustainable dam operation, which will optimize power generation and minimize any adverse effects on bank stability.