Simulation And Study On Hydrodynamic And Water Quality Of Urban Rivers Basde On MIKE21

Urban landscape water plays an important role in regulating urban hydrological environment.However,water quality deteriorates due to poor hydrodynamic conditions and supply shortage.As urban landscape water body,moat of ancient capital not only has functions of flood detention,flood storage and discharge,but also has important historical and humanistic value.This paper,taking xi'an moat,for example,through field monitoring,data collection,using MIKE21 build a set of two-dimensional hydrodynamic-water quality coupling model,and through the model to put forward the moat of filling water control project,screening and optimization,the integrated management to provide the reference for xi'an moat,also provide reference for other urban water governance.Specific conclusions are as follows:(1)The water quality monitoring results of the modified section of the moat show that the maximum value of total nitrogen(TN)appeared in January and total phosphorus(TP)in July.The maximum CODMn value appeared in November,and the maximum algal density and chlorophyll a concentration(Chla)appeared in April.Total nitrogen(TN)concentration in winter and total phosphorus(TP)concentration in summer are the main factors determining water quality.(2)Based on the actual terrain measurement data of the Xi'an Moat,an unstructured grid is selected to establish a two-dimensional hydrodynamic model of the moat.According to the writing principle of the MIKE21 ECOLab module,the secondary development was carried out to obtain a water quality template suitable for use in the Xi'an Moat.By coupling the hydrodynamic module and the water quality module,a two-dimensional hydrodynamic-water quality coupling model of the Xi'an Moat is obtained.The measured parameters in 2017,2018and 2019 were used to calibrate the parameters and verify the model.Verification results show that the model can reflect the dynamics and water quality of the river in the Xi'an Moat.(3)According to the configuration of different water quantity,water position and water quality,six kinds of moat water replenishment control schemes are put forward.The results of model simulation and water quality evaluation show that different schemes have different ability to improve water quality.When the position of the water supply point is determined,the scheme with larger water supply is better than the scheme with smaller water supply;When the water supply is determined,the scheme with relatively dispersed water supply points is better than the scheme with concentrated distribution of water supply points.The fifth scheme with the best purification effect was screened out from the six schemes,and the optimal design was carried out to put forward the regulation measures for water replenishment of the moat:The replenishment points in the southeast corner and the southwest corner were opened,and the replenishment flow was 37,000 m~3/d and 25,000 m~3/d,respectively.In the interval from the east gate to the northeast corner,repeated fresh water supply points were added,the replenishment water was 15,000 m~3/d,and the total replenishment water was 77,000 m~3/d.