Numerical Simulation of Xiangxi River Algal Bloom and the Countermeasures

After construction of the Three Gorges Project (TGP), the hydrodynamic condition in the upper Changjiang River (CJR) course and tributaries in the reservoir changes which caused the Xiangxi River (XXR) -- one tributary of CJR -- algal bloom happen frequently these years. Therefore, a three-dimensional unstructured-mesh eutrophication model has been developed to investigate the dynamic process of XXR algal bloom. Four major interacting systems were simulated, including nutrients (Nitrogen and Phosphorus) cycles, suspended sediment (SS) cycle and phytoplankton dynamics and dissolved oxygen balance. The adsorption-desorption between SS and nutrients and the light shading caused by SS were also considered. Then the model was calibrated and validated by applying it to two XXR algal bloom processes. The simulated time serial concentration of phytoplankton (as chlorophyll) and nutrients were generally in good agreement with in-situ observation. Sensitivity studies were made to investigate different factors' impacts to the chlorophyll concentration, and then countermeasures to XXR algal bloom problem were given.