| Nansihu Lake can be said one of the most important storing lakes in South-to-north Water Diversion Project.Considering that this project is one foundation work with significant strategic meaning for alleviating the worsening water shortage and ecological environment,as well as promoting the overall water-resource optimal allocation,it seems very significant for further deep explorations on the relationships between water quantity and water quality in Nansihu Lake.Based on the summaries and analysis from the predecessors around a large batch of studies on water quantity and quality of the upstream section of Nansihu Lake,with combination of statistical data and information and MIKE21 model,this paper selected internal roughness,pollutant diffusion coefficient and pollutant degradation coefficient as main parameters while taking COD,NH3-N and TP as pollutant indexes selected in the above model.After the careful verifications of the above-mentioned model parameters,it better certified the entire model has certain representativeness and accuracy.By applying the model into simulation schemes for making further simulation analysis,this paper further achieved the detailed simulation schemes,containing the ones applicable to diversion period(October-May(Second Year))and non-diversion period.(June-September).Besides that,it made a series of deep simulation analysis around water-quality changing process in the upstream section of Nansihu Lake in multiple scenarios.And depending on the achieved results,it further analyzed and got the response relationship between water quantity and water quality in the said upstream section.The main achievements of this study are shown as follows.(1)Establish the MIKE21 model of the above upstream section,Carry out simulation of water quality of the above upstream section,use such as Measured runoff data,COD?NH3-N?TP quantity date,conduct model calibration verification.The results are reasonable.(2)Based on the established MIKE21 model fitting for the above upstream section,it further simulated such response relationships under different scenarios for finally achieving the following conclusions.1)The great differences of flow directions and flow rates happening in Nansihu Lake during both diversion period and non-diversion one will have obvious influences in the overall water quantity and quality of Nansihu Lake.Comparing with the overall water level of Nansihu Lake during non-diversion period,the one during diversion period is higher accompanying with larger water quantity and faster flow rate.Therefore,it turned out total quantity of combined pollutants in diversion period is usually fewer than that in non-diversion period.2)Through a series of scenario analysis on the different water quantities of rivers flowing into Nansihu Lake,it concluded more pollutants will be carries when larger water quantity appears.Although pollutant dispersion and mixing rate is relatively higher when flow rate turns faster at the beginning,completing time point of the above mixing process will be delayed at the end.That is to say it'll take more time to reach the goal that third-type water to be covered above 90%of the entire Nansihu Lake.3)Notably,TP degradation rate showed the slowest trend.So,it's of much necessity to focus on monitoring and governing this index in the course of watershed pollution control work.4)Accumulation of pollutants can be easily seen in side of the lake due to failure to complete full degradation.With addition of the shallower water depth in the lake coastal zone and the existences of various aquatic plants,it suggest paying more attention to pollution control work in the lake coastal zone and will be sure to enhance the overall water quality of Nansihu Lake in future water resource governances.(3)For the above analysis results,countermeasures and Suggestions are put forward for pollution control in the upper lake and the basin.To provide theoretical basis for the follow-up water quality of water quality improvement of Nansi Lake. |
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