CONTROL OF FLOOD WATER STAGES AND MORPHOLOGICAL CHANGES IN ALLUVIAL CHANNEL USING NONLINEAR OPTIMIZATION

摘要

This paper presents a simulation-based optimization tool to control flood stages and sediment transport in an alluvial channel (or river) by operating single and multiple floodgates to withdraw flood waters from a channel or river. A well-established one-dimensional open-channel flow model and a non-equilibrium and non-uniform sediment transport model are used to simulate flood flows and bed elevation changes in alluvial channels driven by storm events. An optimization model is developed to solve the adjoint equations of the nonlinear flow equations. A nonlinear optimization algorithm by means of the limited-memory quasi-Newton (LMQN) method is used to iteratively search for the optimal flood withdrawal hydrographs for operating floodgates during a storm period. The searching processing is quick to find the optimal hydrographs for flood control actions. In order to study the effectiveness and applicability of the optimal control theory, an alluvial channel with single and multiple floodgates are considered under complex hydrological conditions, sediment properties, and channel geometry. The changes in morphology due to optimal control of flows are studied thoroughly. It is found that the influence of morphological changes on flood control varies with number of control structures, hydrological and morphological conditions.