Flood Control through Engineered Avulsions and Floodways in the Lower Yellow River

Due to high in-channel sedimentation rates, the Yellow River Delta of China has changed course frequently in its history, with huge socioeconomic impacts. The following questions are addressed: What is the best timing and location of deliberate avulsions? Can temporary floodways lessen the cost and flooding impacts of avulsion strategies? To address these questions, a simulation-based optimization model is developed that is novel in its integration of economics, hydraulics, and sediment dynamics. The framework considers tradeoffs between the cost of avulsion-mitigation strategies and expected flooding risk. Four design variables (avulsion timing and location, floodway size, and operation rule) are optimized. The results suggest that locating the deliberate avulsion as far upstream as possible reduces total cost. However, the level of reduction of channel capacity at which a deliberate avulsion should be triggered is sensitive to assumed cost parameters. Meanwhile, the optimal floodway size is either the largest possible size or none at all, depending on the frequency of avulsion and floodway cost. Floodway costs influence decisions less than costs of avulsions and flood damage costs. (C) 2019 American Society of Civil Engineers.