Effect of flow regulation on streambank erosion: A perspective downstream of a flood control dam, Kansas, USA

Abstract

AbstractWhile large dams provide society with many benefits, there are many environmental trade‐offs. One trade‐off of dam installation is the morphologic changes that ensue in the downstream channel. Channel widening due to streambank erosion is a common response to flow regulation (FR), but dominant erosion processes and rates have rarely been evaluated downstream of dams. This case study investigates how a 75‐year‐old flood control dam has affected downstream bank erosion on the Lower Smoky Hill River, located in central Kansas, USA. A one‐dimensional hydraulic, sediment transport, and bank erosion model was used to assess changes in erosion processes and rates with and without FR up to 86 river km downstream of the dam. The model showed that toe erosion was the dominant bank erosion process for both with and without FR scenarios. While toe erosion rates were significantly higher (α < 0.05) under the without FR scenario, more days of toe erosion occurred under the with FR scenario. More days of toe erosion are attributed to the change in the flow regime, with moderate flows (between 5% and 40% daily exceedance probability) increasing and hydrograph rise and fall rates decreasing since dam installation. Furthermore, it was observed that pioneer riparian vegetation may drown out during long duration, high‐flow events brought on by FR, amplifying erosion rates. These results provide broader insight into morphological responses to flood control dams, highlighting the effect changes in flow regime can have on downstream channel morphology and identifying major challenges in managing streambank erosion downstream of dams.