Study On The Water Quality Standard Management Plan Of The Bahe River Basin Based On WASP Model

The Bahe River Basin is the connection zone between Qinling Mountains mountainous area and Weihe River,a link between Xi'an's General Planning Ecological Zone and the umbilical zone of Xi'an Economic Development Zone.In recent years,the population in the Bahe River Basin has been increasing by years,demands for quality of life are also growing.There are many problems such as lacking of water,serious pollution and ecological imbalance,which affect the living conditions and economic level of the residents.Therefore,it is necessary to understand in detail the major pollutants in the Bahe River Basin,the degree of pollution of different types of pollution,river water bodies'ability to degrade pollutants and their remaining capacity,based on the basic scenario,a management plan was proposed,it is of great significance to solve people's livelihood issues and sustainable economic development.This paper took the Bahe River Basin as the research area to carry out water quality monitoring and assessment.The 2015 annual automatic monitoring statistical data was used to calculate the point source pollution,and the non-point source pollution load was calculated by the model of the loss output coefficient of the basin.The WASP model was used as a tool to analyze the relationship between water quality and pollution load.Targeted the functional areas as targets,the TMDL plan will be used to allocate and reduce pollution loads in the river basin and establish a water quality management model for the pollution sources in the Bahe River basin.The research results are as follows:?1?From 2015 to 2017,the average ratio of ammonia-nitrogen single-factor indexes which were greater than 1 were 71.42%,61.9%and 66.67%respectively in the 21 monitoring sections of the Bahe River basin.In the section of Bahe Bridge on Qinhan Avenue,the arithmetic mean values of ammonia nitrogen,TP,and TN concentrations during the rainfall period were less than 3 arithmetic mean values of ammonia nitrogen,TP,and TN concentrations during the non-rainfall period.Compared the five rainy rainfall processes,when the water level was low,the concentrations of ammonia nitrogen,TP,and TN were high,when the water level was high,the concentrations of ammonia nitrogen and TN were low,but the concentration of TP had no significant change.Compared with the three non-rainfall period monitoring,when the water level was low,the concentrations of ammonia nitrogen,TP and TN were higher.During the rainfall period,the mean values of 0.16 for ammonia nitrogen,TP,and TN RSD were greater than 0.06 for non-rainfall period RSD.?2?In 2015,the amount of ammonia nitrogen entering the Bahe River Basin was 1098.79 t/a,and the point source pollution load was 240.12 t/a,the non-point source pollution load was 858.67 t/a in Which livestock and poultry farming>Land use>Point source pollution>Rural life.Among the non-point source loads,43.8%came from livestock and poultry farming,15.6%came from rural life,and 40.6%came from different types of land use.?3?The river was generalized into 14 segments,the measured value of ammonia nitrogen degradation coefficient was obtained by field measurement.The results showed that:the ammonia nitrogen degradation coefficient was positively correlated with the flow rate.Ammonia nitrogen degradation coefficient(mean value 0.39 d^-1)during the rainfall period was greater than the non-rainfall period ammonia nitrogen degradation coefficient(mean 0.23 d^-1).Ammonia-nitrogen degradation coefficient values varied between 0.21-0.46 d^-1during 5 rainfall periods and 3 non-rainfall periods during flood season,the model parameters were taken as the mean 0.31 d^-1.?4?After parameter calibration and model verification,it showed that the model could be used as an effective tool for water quality prediction and management in the Bahe River Basin.The basic scenario showed that the rate of compliance of the whole river reaches the dry period?November-February?was38.45%,the flat water period?March-June?was 25.26%,the wet period?July-October?were not up to standard.Scenario simulation showed that the reduction of load to a certain extent guarantees that the water quality was up to standard,and the rate of reaching the standard in the whole river basin reaches up to 89.28%in the dry period and 73.02%in the wet period.?5?Based on the actual 50%guarantee rate of the actual flow value?1991-2010?of the Maduwang hydrological station in the past 20 years,calculated the water environment capacity of ammonia nitrogen in the Bahe River Basin as 303.70 t/a.In order to achieve the target area of the functional area,the total non-point source reduction rate of the upper reaches of the Bahe River exceeded 70%.The top three non-point source reductions were:Seg3?148.71 t/a?>Seg1?140.61 t/a?>Seg4?104.35 t/a?.Therefore,the water quality management of the Bahe River Basin can be divided into sub-basins,sub-levels,and seasonal cuts.The upper reaches of the river basin should focus on the control of non-point source pollution,optimizing the types of land use,and promoting the large-scale development of livestock and poultry farming.Controlling point source pollution in the lower reaches of the river basin,a system management system should be established from the generation of pollution load to discharge.The maximum allowable discharge amount should be calculated according to the seasonal flow rate and carried out the dynamic management of the river basin.