Research On Water Quantity And Quality Operation Of Multiple Water Sources And Effects Of Rainstorm Runoff On River Water Quality

Water resources should be valued not only the quantity but also the quality.With the development of social,economic and ecological environment,the demands of the water quantity and the quality are increasing day by day.This requires the joint operations and the overall planning of water resources in river basins.For Northern China,the utilization of water resources is inefficiency under the impacts on the geographic location and the climate,etc.It leads the contradiction of water resources supply and demand.Moreover,to satisfy the needs of landscape,hydraulic structures lack effective regulations,which cause the poor connection of river networks and the low self-purification of water body.Furthermore,with the urban development,non-point source pollution caused by storm runoff is gradually becoming the main contributor to pollutant loads in urban water bodies.A large quantity of pollutants is washed off by storm water during rainfall events,which deteriorate the river water quality rapidly.These above factors let the northern rivers own a poor water environment carrying capacity and the water ecological problems boom frequently,which is not conducive to the sustainable development of society,economy and environment.Taking the river network composed by Beiyun River,Longfeng River and the canal in Wuqing district as an example,based on the numerical model,this paper carried out the studies of the schemes of river networks connection and circulation,the joint operations of water quantity and quality of multiple water sources,the influences of joint operations factors and the effects of rainstorm runoff on river water quality in urban areas.These studies can provide data support for the water resources managers to improve the regulation of water resources.The key objectives and results of the present paper include:(1)The trend of water quantity and quality in study area was analyzed.Then the hydrodynamic and water quality model was constructed by Infoworks ICM according to the river networks and measured data.The results show that there is an increasing trend for annual water quantity.The annual average runoff concentration degree is0.46 and the runoff concentration period is July to October.TN and TP are the main pollutants in rivers.The R~2,NSE and PBIAS were used to evaluate the numerical model performances.The results show that most of the R~2 and NSE are above 0.58and 0.47,and the PBIAS is controlled within 30%for most simulations,which indicates the applicability and reliability of the model.(2)Considering the characteristics of river networks and available water supply,the scheme of river networks connections and local water circulation was presented,and the effect of the scheme was evaluated by the numerical model.The simulation results illustrate that,for river networks connections,the water diversion ratio should be approximately kept at 1:1 between Beiyun River and Longfeng River when the Danan Gate is operating.Under these conditions,the average concentration improvement rate and the standardized rate of water body are 54%and 0.82,respectively.Moreover,the hydrodynamic condition of the local water circulation is suitable when the flow of the 7th,the 5th,the 2nd and the 1st channel are 1.0,1.0,0.7and 1.3m~3/s,respectively.However,due to the shortage of water supply,the average concentration improvement rate and the standardized rate of local water circulation are approximately 40%and 0.62,which means the effect of water quality improvement needs to be enhanced.(3)The ecological water requirements of different classes of the study region were calculated.The numerical model was used to estimate the advantages and disadvantages of the multiple water sources operation schemes.Then,the appropriate scheme and river ecological target were confirmed.The results display that the annual ecological water requirements under five classes is 16.74 to 93.12 million m~3.The ecological class of the river could be maintained as minimum if the upstream water was utilized.However,the demands of the ecological water could be effectively improved by using reclaimed and external water.Under the water quantity and quality operations of multiple water sources,the average concentration improvement rate and the standardized rate increased to above 60%and 0.95,respectively.The river ecological target could be maintained as middle and satisfied the long-term goal.(4)The impacts of water discharge,water quality,concentration of water,the peak time of discharge and intermittent operation on river water quality and water resources utilization efficiency were analyzed based on numerical simulations.The results find that the improvement of water quality is mainly determined by the water quality,while the time required for water quality improvement is controlled by the water discharge.Increasing the water discharge can accelerate the water quality improvement processes,but the consumption of water resource will increase when the same concentration is gotten.The additional water volume is approximately10%～60%.The consumption of water resources is the least when adopting the operation scheme of high water quality,low peak and average water diversion.However,using appropriate proportion of water resources in the early stage of water diversion can improve the river water quality more rapidly with a slight increase in water consumption.(5)The effects of surface runoff pollution on river water quality in urban areas under different rainfall conditions were analyzed.The surface runoff pollution model of Wuqing district,Tianjin,was constructed based on the data of land uses,pipe networks,field measured pipeline velocities and surface runoff samples.Then,the surface runoff pollutions were simulated under the 1a,2a,3a and 5a rainfall conditions.Simulation results demonstrate that the event mean concentrations(EMC)and the peak of the river pollutant concentrations were the highest under the condition of the 1-year return period.With the increase of return periods,both the two indexes decreased gradually.The increase of runoff not only enhances the dilution of pollutants,but also shortens the retention time of pollutants in rivers,which are the main reasons for the decrease of water pollution.