Numerical Simulation Of Rural River System Interconnection

The water system in the plain river network is well developed.With the economic development and human activities,the original connection between the rivers is broken,the connectivity of the water system is deteriorating,and in addition to the heavy use of pesticides and fertilizers,the eutrophication of water bodies occurs from time to time.Environmental issues are becoming increasingly severe.The eutrophication of the water ecosystem depends not only on the nutrient loading in the water,but also on the impact of hydrodynamic conditions.After the river network is connected,the improvement of river hydrodynamic conditions has a positive effect on the self-purification of water bodies and the improvement of river water quality.This paper takes the river network of the Shenhaiwei Rural Wetland Park in Fuwei village,Changshu city as the research area.Based on the river water level,the shape of the river section and the river water quality,the water system structural connectivity evaluation system is used to study the connectivity and differences of different structures in the river system.The river water quality status under the connected path was simulated.The suggested guidelines for rural river system connectivity design in the plain river network area was put forward to provide theoretical reference and practical guidance for the river system of regional river system restoration,repair and planning.The main research results of this paper are as follows:Suggested guidelines for rural river system connectivity design in the plain river network area(1)Environmental MonitoringThe RISEN-SFCC ultrasonic depth sounder was used to measure water depths at each section of the river,and the shape of the cross-section of the river was calculated.427 actual river sections were measured within two months.After sampling and detecting the river network water in the study area in different seasons,it was found that 94% of the nitrogen in the water was inorganic nitrogen,and the phosphorus was mainly in the form of organic phosphorus.The average concentration of total nitrogen in the river reaches 3.09 mg/L,and the average concentration of total phosphorus is 0.24 mg/L.Both of them are of inferior V water body standards and are in urgent need of treatment.(2)Model construction and simulation analysisBased on the Mike11 model,this study constructed a hydrodynamic model of the river network in the Chenhaiwei Park.Based on the hydrodynamic model,a hydrodynamic-water quality model was constructed based on the AD module and the eutrophication template in the EcoLab module.Twelve indicators such as ammonia nitrogen,nitrate nitrogen,total nitrogen,phosphate,total phosphorus,and chlorophyll-a were selected as state variables,and the main simulation parameters were the total nitrogen and the total phosphorus.In this paper,the water quality of the rivers under the condition of connectivity of different water systems was simulated using the method of water structure connectivity evaluation and the Mike11 model simulation.The main existing forms of nitrogen and phosphorus in the water of the river network of the Chenhaiwei Wetland Park are inorganic nitrogen and organic phosphorus,respectively.The simulation study found that the degree of water circulation was positively correlated with the degradation effect of TN,and negatively correlated with the degradation effect of TP.The river network is designed to be a tree-like river network(without loops).The degradation of TN is better,and the river network is designed to have a good degradation effect of TP when it is a circular river network with excellent degree of ringing(0.06~0.08).The connection rate of river nodes is positively correlated with the degradation effect of TN and TP.The higher the node connection rate,the lower the simulated concentration of TN and TP and the better the degradation effect.The higher the degree of hydrological connectivity,the lower the concentration of TN and TP,and the more significant effect of TN degradation.In addition,simulations have found that when rivers are connected at confluence,water quality improvement is better.