Study On Main Contamination Fluxes Of Water Environment In The Qiantang River

The quality of water environment in the Qiantang Riverbasim is crucial to the sustainable development of regional economy and society.For water environment protection,it is of great significance to keep the water environment capacity scientific and sustainable.Therefore,the research on the contamination discharge capacity, especially the total discharge capacity of NH₃-N(ammonia-nitrogen)and TP(total phosphorus),is urgent.The strategy of control over total capacity is based upon the research of fluxes where the water environment corresponds to its function.Since the water environment capability usually has a dynamic change,contamination fluxes research on different hydrological conditions is of great necessity.Taking the Qiantang Riverbasim as the research object,this paper integrates environmental evaluation technology,system dynamics theory,water environment spatial modeling technology,scenario analysis method to make numerical simulation of water environment flow field and the main contamination of different scenarios.In the research the temporal-spatial rule of water environment flow field and its process dynamic theory have been analyzed,the contamination fluxes transformations rule and trend have been explored,a visualized GIS-based system for water environment and quality prediction and contamination fluxes decision-making have been developed,making the research results visible.The main conclusions of this paper are as follows:(1)Flow field simulation of the Qiantang Riverbasim and its influence on the contamination diffusionThe paper takes a hydrographic survey(year 2006),and verifies the numerical simulation and its reliability in the researched regions.In the high water period,three measuring points have been taken for validation,separately locating in the left,middle and right of each section.The result shows that the range of flow error is below 27% with an average error about 12%,velocity error is below 12.2%with an average error about 6%.In the accordant junction of the Lan River in the upper,there exists circumfluence in the three hydrological periods,with a remarkable influence in the high water period and normal period and relatively inconspicuous influence in the low water period.In the accordant junction of the Puyang River in the lower,there also exists circumfluence in the high water period and normal period,with slight movement of river water,and it has little affect on the mixture of contamination from the Puyang River to the Qiantang River.(2)The temporal-spatial transformation rules of the main contamination in the Qiantang RiverIn general,the water quality of the Qiantang River system is good from year 2001 to 2005,among which the ClassⅠ～Ⅲwater accounts for more than 50%and the water quality of almost half of the sections can fit the regional water demand. Here is the temporal-spatial rules and characteristics of NH₃-N and TP:NH₃-N concentration has an remarkable rule with the change of time in the upper river,rising up from high water period,normal period to low water period,and in these three periods the concentration rises up from the first section to the Yanlingwu section and then reduces,especially in the Fuchun river.The TP concentration changes with time below the section of the Fuchun River:high concentration in high water period and low in dry season and spatially no such obvious transformation rules.(3)Fluxes simulation of the main contamination and analysis of the temporal-spatial transformation rule in the Qiantang RiverThis research proposes a strategy of contamination fluxes based on scenario analysis.The fluxes of NH₃-N and TP of different hydrological conditions have been simulated.And the characteristics of allowable fluxesâ–³T trend,proportion characteristics of different hydrological level years and different water periods have been analyzed.Of the five kinds hydrological years,especially high flow year,high flow year,normal flow year,low flow year,and especially low flow year,the respectively allowable contamination fluxes valueâ–³T are:NH₃-N,11544.49 t/a,11250.14 t/a,10949.23 t/a,10627.72 t/a,10208.91 t/a;TP,3701.96 t/a,3625.77 t/a,3546.37 t/a,3455.59 t/a,3303.26 t/a.Based on the water environment spatial data mining and visualization method, the paper presents these main characteristics and innovations:â‘ Measurement of contamination fluxes:A scene-based research strategy is proposed:measurement /water quality analysis→flow field simulation→contamination transformation rule→fluxes scene simulation→temporal-spatial rule analysis.â‘¡Serial numerical models of water environment in the Qiantang River:The controlled equations of the flow field model of the main river,united controlled equations of the main contamination fluxes and water quality prediction model at emergent time are set up.â‘¢GIS-based water quality and contamination fluxes decision-making assistance system:A water environment database has been set up;based on MapX and C#.net platform,a system has been developed to facilitate visual inquiry,decision-making and graphics export.