Study On The Suitability Of The Water Quality Simulation Of The Beichuan River By The WASP Model And The QUAL2K Model

Water plays an important role in the survival and development of mankind.For the relatively scarce freshwater resources,the existing surface water bodies and underground water bodies are scarce.With the rapid development of our country,the damage to the water environment is also very serious.In order to simulate the water environment,foreign scholars first studied the method of simulating the water by using the water quality model to make the complex water body relatively simplified.At present,the method of using the water quality model to simulate the water body has been widely used.Therefore,we simulate and analyze water quality by using the water quality model.The existing research is mainly based on the application of a water quality model,and it does not consider whether the selected method is suitable for the research area.In this paper,two models of water quality simulation were applied in the same area,and during the comparative analysis,fixing a more suitable water quality model for the research area.Based on the data of hydrological and water quality,meteorological data and pollutant load of Beichuan River,the WASP model and QUAL2K model were constructed to simulate the main stream of Beichuan River.Overall,the effect of WASP simulation model of Beichuan River water quality is relatively good,the simulation results of BOD₅,ammonia nitrogen,total nitrogen and total phosphorus showed that the average relative error in the calibration period were 9.57%,7.01%,59.21%and 7.32%,relatively.In the verification period,BOD₅,ammonia nitrogen,total nitrogen and total phosphorus of the average relative error were 9.52%,14.42%,47.32%and 26.47%.The overall simulation results were good except for total nitrogen.The simulation results for BOD₅,ammonia nitrogen,total nitrogen and total phosphorus in the QUAL2K model shows that the average relative error in the calibration period were 14.78%,16.97%,39.27%and 17.07%,the simulation results,but the larger relative error in the verification period BOD₅ and TP in the verification period,BOD₅,ammonia nitrogen,total nitrogen and total phosphorus the average relative error was 25.00%,62.02%,17.67%and 58.82%,relatively.Judging from the relative error analysis,WASP model has a better simulation effect on Beichuan river body than QUAL2K model.Afterwards,the two models separately change the flow,water temperature,and pollutant load,and explore the change of the water quality.Adjusting the flow rate,water temperature,and pollution load to-20%,-10%,10%,and 20%,respectively,through multiple simulations,the corresponding BOD₅,ammonia nitrogen,total nitrogen,and total phosphorus concentrations at the outlet were obtained.Comparing with the actual water quality of the Beichuan River,the water quality situation was compared and analyzed to investigate the effect of flow,water temperature and pollution load on the water quality of the effluent.The results showed that the greatest influence on the effluent quality of the two models was the load of pollutants,followed by the upstream runoff and the final temperature.Although the results of the two models have a certain difference in the simulation of individual pollutants,the results of the impact are mostly consistent.This study taking BOD₅ as an example,the sensitivity of the two models to input conditions is analyzed.From the point of view of flow,water temperature and pollutant load,the sensitivity of the QUAL2K model to the three indexes is more sensitive than that of the WASP model.The results of analysis of ammonia nitrogen,total nitrogen and total phosphorus were similar to those of BOD₅.