Model-Based Method to Establish Total Pollution Load Control Objective for Looped River Network

A water quality model was developed for the surface water system made up of looped river networks. It consisted of a hydrological sub-model and a water quality sub-model. The former was built up based on the Saint Venant equations, while the latter modified the traditional CSTR taking the uncertain flow direction into account. What the model described was the temporal and spatial changes of COD, NH₄-N and DO concentration of the looped river network. By utilizing the prediction function of the model, a method for establishing the pollution load control objective has been given. Through Monte-Carlo-based model running, a series of pollutant load scenarios which met the water quality requirements could be produced. The scenario with maximum load can be used to determine the load control objectives. With the case of Lucheng River Network in China, the model has been calibrated and the load control objectives for COD and NH₄-N have been brought forward.