Research On The Salinity Control Of Northern Coastal City Water System Based On The Surface-underground Joint Simulation

Coastal cities are important area for our country's economic development,and its ecological and environmental issue have gradually become a hot spot of concern.The salinity of groundwater in coastal cities is generally high,which affects the salinity of urban water systems,which in turn limits the health of aquatic vegetation communities and river and lake systems.Especially the coastal cities in the northern plains,due to the overall shortage of fresh water resources and the poor mobility of urban water systems,the problem of excessive salinity of surface water bodies is more prominent,and it has gradually become an factor which restricting the improvement of the local ecological environment.In order to alleviate the problem of salinity in urban water systems,it is necessary to start with the process of groundwater and surface water exchange,clarify the changes of salinity in coastal city water systems,and propose control objectives and control methods for water salinity.This article takes Dongying city center as a typical case,on the basis of identifying the changes of water salinity and influencing factors,through the reasonable determination of salinity control objectives,the selection of control methods,and the formulation of control schemes,the salinity control of coastal city water systems is developed.The specific research undertaken includes:(1)Analysis of the change law of salinity in coastal citiesFocusing on the city center of Dongying,a typical coastal city,combining the monitoring data of surface water and groundwater,the spatial and temporal changes of salinity in the water system of the coastal city are clarified.By comparing the changes in precipitation,river level,groundwater level and surface water salinity in different periods,the influencing factors of water salinity are identified.The change and distribution of salinity in urban water systems are related to groundwater salinity concentration,surface water and groundwater level difference The more the groundwater level is higher than the surface water,the faster the surface water salinity increases,and the higher the maximum salinity of the water system,and is more similar to the groundwater salinity,otherwise the slower the increase rate,and the lower the maximum salinity.(2)Study on salinity tolerance of typical aquatic vegetationCarry out the salinity tolerance experiment of typical aquatic plants,explore the salinity tolerance threshold of aquatic plants,so as to determine the reasonable target of surface water salinity control.Select different types of aquatic vegetation,monitor the changes of relevant biochemical indicators under different salinity concentrations,and study the stress status of plants with different salinity concentrations.The results show that representative water plants—cattail,representative floating leaf plants—Water lily,representative submerged plant—Myriophyllum spicatum can not grow in water body with salinity of 2000mg/L,and grows well at salinity of 1000mg/L.Considering the current situation of Dongying City,it is recommended that the salinity control target be 1000mg/L in the near future.In the long term,the requirements will be further improved according to the situation.(3)Construction of surface-groundwater salinity coupling modelBased on the MIKE SHE and MIKE 11 models,a surface-groundwater salinity coupling model in the downtown area of Dongying was constructed.The model combines the MIKE SHE distributed hydrological model to simulate regional groundwater level and salinity changes,analyzes the surface-groundwater salinity exchange process,and uses this as an input condition to carry out a joint simulation of surface water hydrodynamic water quality with the MIKE 11 model.Combine with the hydrological station and urban water system main control section length series of monitoring data for model parameter calibration and verification.(4)Development of water salinity control planCombined with the surface-groundwater salt coupling model,through the joint simulation of hydrodynamic conditions and salinity under different water replenishment schemes,the optimal scheme of ecological water replenishment was determined.Simulate the changes of the salinity of the surface water body under the continuous water replenishment with low velocity and high velocity,and the regular water exchange program with different water exchange cycles.Under the continuous water replenishment scheme,the salinity of the low velocity scheme in the ordinary water year can be controlled below 800mg/L,and the high velocity scheme can be controlled at 500mg/L.The salinity of the two schemes is within the control target.The water needs is 360 million m3 of the low velocity scheme,and 790 million m3 of the high velocity scheme.Due to the limited water diversion index in the study area,it is recommended to select the low-velocity plan.Under the regular water exchange program,the water exchange cycle required to control the salinity of the water below 1000mg/L is 15 days,that is,exchange the water exchange twice one month can protect the health growth of aquatic plants,needs about 380 million m3 water.According to the precipitation law and the impact on the salinity of the water body,it is recommended to adopt a dynamic water exchange cycle,with a 15-day water exchange cycle from March to May,a 90-day water exchange cycle from June to November,a 30-day water exchange cycle from September to November,and no water change during the freezing period from December to February.The change of water exchange cycle can control the salinity of the water body in the study area below 1000mg/L and only needs 200 million m3 water.