Study On Hydrodynamic-ecological Model In Urban Lakes

As an important carrier of water resources in arid regions,lakes maintain the balance of regional ecosystems and provide economic development needs with their unique ecological structure functions.Urban lakes are often more closely related to humans and are subject to human disturbances,resulting in a series of water environmental problems,In order to facilitate the promotion of urban lake water environment management,and give full play to the ecological and economic value of urban lake water supply,flood control,climate fine-tuning.cultural entertainment,aquaculture,etc.,this paper takes Chanba lake,Xi’an City Ecological Region,as the research object,and continuously monitors it.The water environment characteristics of the lake area,the two-dimensional hydrodynamic model of the lake was constructed,and the flow field characteristics of the water body in the lake area at various frequency years were simulated and analyzed.By constructing a mathematical model of urban lake water ecological dynamics,the temporal and spatial distribution characteristics of each state variable are analyzed.On the basis of the simulation results,combined with the comprehensive nutritional status index method and principal component analysis method,the nutritional status of the lake water body was evaluated and the main factors causing the eutrophication of the water body were analyzed.Specific results are as follows:,The ecological characteristics of the water environment at 9 points in the lake area were continuously monitored,and there was no obvious change law between the water environment factors in the time distribution.On the spatial distribution,the water quality of the Chanhe River is worse than that of the Bahe River,and the downstream water quality is significantly worse than the upstream.The effluent quality of the two sewage treatment plants at the S3 and S8 points is the worst.The bacterial community richness of the six groups of water samples was S8>S3>S4>S9>S7>S1,and the diversity was S8>S9>S7>S4>S1>S3.The main groups of microorganisms at the Phylum-level classification are Proteo:bacteria,Bacteroides,and Cyanophyta.The hydrodynamic model of the study area was established by MIKE21.The flow field characteristics of the study area under different hydrological frequency conditions were simulated.Under the different frequency years,the average flow velocity of the study area changed little,from high to low.P=10%,P=50%,and P=90%,the flow rate increases correspondingly in complex terrain changes and rubber dams.At the intersection of the Chanbahe river,due to the influence of the flow of the Chanhe River,the flow field of the Bahe river changed correspondingly,and the flow vector arrow was partially deflected to the right.The water ecological dynamics model was constructed by MIKE ECOLAB module.The model was used to calculate the time and space distribution of water quality indicators under different hydrological frequency conditions.The results showed that the TN concentration had seriously exceeded the V water limit(2.0mg/L).TP concentration belongs to surface class Ⅱwater.CODMn is surface type IV water.DO is better than surface type Ⅰ water,and the concentration of Chla decreases gradually from upstream to downstream along the whole area.The SD level is uniform.Comprehensive assessment of the annual water quality grades of each frequency,the water quality of the Baihe River is basically stable in Class Ⅱ before entering the confluence zone,and the Chanhe River water body is Class Ⅳ.The evaluation of nutrient status of the water showed that all the 9 monitoring points were in a eutrophic state.During the three frequencies,the water in the study area was dominated by mild eutrophication,and the water in the Bahe River was in the spring of P=50%frequency year and P=90%.In the autumn and winter of the frequency year,some water bodies show a nutrient state.Principal and secondary driving factors for water eutrophication were obtained by principal component analysis(NO2-N,NH3-N,DO);the measured points were ranked,and the top scores of S8,S3 and S4 were obtained.