Development and application of a two-dimensional water quality model for the Daqinghe River Mouth of the Dianchi Lake

Water quality models are important tools to support the optimization of aquatic ecosystem rehabilitation programs and assess their efficiency. Basing on the flow conditions of the Daqinghe River Mouth of the Dianchi Lake, China, a two-dimensional water quality model was developed in the research. The hydrodynamics module was numerically solved by the alternating direction iteration (ADI) method. The parameters of the water quality module were obtained through the in situ experiments and the laboratory analyses that were conducted from 2006 to 2007. The model was calibrated and verified by the observation data in 2007. Among the four modelled key variables, i.e., water level, COD (in CODCr), NH4+-N and PO43- -P, the minimum value of the coefficient of determination (CoD) was 0.69, indicating the model performed reasonably well. The developed model was then applied to simulate the water quality changes at a downstrearn cross-section assuming that the designed restoration programs were implemented. According to the simulated results, the restoration programs could cut down the loads of COD and PO43- -P about 15%. Such a load reduction, unfortunately, would have very little effect on the NH4+ -N removal. Moreover, the water quality at the outlet cross-section would be still in class V (3838-02), indicating more measures should be taken to further reduce the loads. The study demonstrated the capability of water quality models to support aquatic ecosystem restorations.