Simulation Of Hydrodynamics And Water Quality Of Mountain River Based On EFDC

The process of China’s urbanization has been posing serious threats to the waterenvironment. The expansion of the city, to a large degree, changes previoustype of landuse and increases the load of non-point source pollution, resulting in a large number ofrivers and lakes suffer serious pollution, and some are even confronted with thedisappearance of ecological function. How toprotect and govern urban river’s waterquality has become a focus ofthe research of water environment. Water environmentresearch involves a large scale of space, numerouspollutant compositions and complexenvironment process, so it will be very difficult if only use experimental analysis andfield monitoring. Establishing a mathematical model to realize the numerical simulationand reaserching river evolution law to guide the river water environment protectionhasbecome the focus in the field. Based on EFDC (Environmental Fluid Dynamics Code)model, the thesis takes Zhaojiaxi River in Liangjiang New Area in Chongqing as anresearch object, and through which build the hydrodynamics and water quality model ofZhaojiaxi River has been established in this thesis according to the hydrology and waterquality monitoring data of Zhaojiaxi River. This study is carried out as follows:①Generating the orthogonal curvilinear grids according to river water boundaryon Delft3D software platform，which boast of1872cells in a horizontal direction and4layers in the vertical direction. Building3D River bathymetry of Zhaojiaxi River on thebasis of acoustic doppler current profiler date of13river section.②Accroding to the hydrodynamic model of Zhaojiaxi River based on EFDCmodel,the hydrodynamic field, temperature field Zhaojiaxi River all the year round aresimulaterd, and the result shows thatthe average relative error offlow velocity, waterlevel, temperature sitimulationare respectively23.42%,8.8%and6.42%. The analysisof flow field characteristicsshows that wind-driven current is the main driving force onthe flow of water body inthenormal season. Dye tracer shows that it needs50days toreach a stable concentration for downstream.Water age analysis shows that the waterageincreases graduallyfrom upstream to downstream and gets more than180days in thedownstream.③Building water quality model by hydrodynamic model, which is used to simulateNH3-N, COD, TP, Chl-a. Simulation result shows average relative error are20.54%、23.70%、27.1%、21.94%in the parameters calibrationwith6times water quality monitoringdate, and20.47%、27.84%、31.3%、28.46%in the verification with7timeswater quality monitoringdate.④Total carrying capacity of TSS, NH3-N, COD, TP, TN in Zhaojiaxi River reach45.76t/a、1.03t/a、15.12t/a、0.53t/a、4.68t/arespectively. When the water quality targetof Zhaojiaxi River is set as surface water IV class quality, aquatic environmentalcapacity of TP, TN as restrictive indicators reach3.91t/a、0.26t/a with the target ofsurface water IV class quality, then with a reduction quantity of0.27t/a,0.77t/a.⑤Based on the hydrodynamics and water quality model of Zhaojiaxi River, twocases are simulated:1) The simulation at different wind speed of3m/s、5m/s、10m/swith constant direction shows that wind-driven current has a great influence on flowfield, and the surface velocity get0.01m/s、0.02m/s、0.05m/srespectively;2) Water age ofupstream and downstream reach5days and22daysrespectively when external drainageof1m3/s from Jialing River. Under this circumstance, the three water quality index,NH3-N、COD、TP reach stable value on the30th day,which is0.16mg/L、3.0mg/L、0.2mg/L or so.⑥This study proposes a set of water quality protection technology based onconstructed wetlands, grassed swales and step pool system about Zhaojiaxi River.