Dynamic Water Environmental Capacity And Risk Assessment Of The Yellow River At Huhhot

Water environmental safety is directly related to national economic security and social stability. With the continuous development of social economy,there is an increasing need of water requirement and water displacement.While in the water shortage at the same time,sewage discharge is not coordinated with the water environment capacity, so that the water environment of the river basin is increasing deterioration.Therefore,based on dynamic water environmental capacity study providing pollution emission guidance for emission firm and gauge of pollution gross control and protection countermeasure for administrative department is the cornerstone of basin water environmental restoration.the Yellow River at Huhhot was used for this paper,Through analysis the pollution source distribution-. pollutant contribution amount and exceeding standard pollutants,to determine the calculation factors of dynamic water environmental capacity using single factor index method based on the actual situation water quality and the characteristics of the water pollutants.The Yellow River at Huhhot are divided into 7 control sections and key control sections are chosen according to the main sream function zoning and waste water discharge position.1-D dynamic water environmental capacity of the Yellow River at Huhhot and 3-D dynamic water environmental capacity of the water diversion project from the Yellow River to Huhhot are analyzed using the 1-D、3-D hydrodynamic and water quality coupling model based on the hydrology,water quality, regional meteorological data of the 9 sections of the Yellow River at Huhhot.Based on the dynamic water environmental capacity,the paper calculates the environmental risk value of each pollutants to evaluate the risk level and the countermeasures to protect water quality is put forward.The main conclusions of the paper are as follows:(1)Based on the ECOLab module in MIKE,the ice sheet model is built for the one dimensional hydrodynamic model,which is the relationship between the total water level、the liquid level and the ice sheet thickness.The main parameters of water quality include degradation coefficient temperature coefficient and other 30 items,the main parameters of hydrodynamic forces is rough rate and ice sheet and wind are the main features of Hohhot the Yellow River section,after the model debugging and calibration.The relative error and the Nash-Sutcliffe coefficient of simulation value and measured value of hydrodynamic and water quality after the model calibration are ≤15%、≥0.9 and≤20%、≥0.8.The water level error interval and the discharge error interval are≤<0.19m、≤27m3/s.The error intervals of DO、COD、BOD、NH3-N、TP、 NO3- and FC of all calibrated sections are≤0.09mg/l、≤0.28mg/l、≤0.10mg/l、≤0.11mg/l、 ≤0.076mg/1、<0.13mg/1　and≤203/1.This precision can meet the requirement of dynamic water environment capacity calculation accuracy.(2)The dynamic water environment capacity variation range of DO、COD、BOD、 NH3-N、TP、NO3-、FC of the Yellow River at Huhhot are 839.94～2506.38t/d、-167.03～ 3482.44t/d、324.36 ～1330.44t/d、-74.00 ～370.84t/d、14.11～64.14t/d、1026.98 ～ 4032.54t/d、747.11×106～4112.12×106/d.Non frozen period is greater than the frozen period of dynamic water environment capacity of each pollutants.Non frozen period of the maximum dynamic water environment capacity of each pollutants in Aug、Sep and Oct,March、April and November centered,Mar、Jun and Jul minimum,excepting COD and NH3-N.(3)Vertical dynamic water environmental capacity of each pollutants is slightly different of the intake water diversion project from the Yellow River to Huhhot.The dynamic water environment capacity variation range of DO、COD、BOD、NH3-N、TP、 NO3-、 FC of 1～4 layers are 39.91～231.55t/d、-50.56～389.51t/d～4.35～107.14t/d、 4.87 ～57.46t/d、1.63～ 7.50t/d、139.59 ～558.20t/d、80.45×106 ～ 568.42×106/d.Non frozen period is greater than the frozen period of dynamic water environment capacity of each pollutants.Non frozen period of the maximum dynamic water environment capacity of each pollutants in Aug、Sep and Oct.(4)The influence of flow is greater than comprehensive degradation in water quality process of the dynamic water environment capacity.The dynamic water environmental capacity of each pollutants has obvious fluctuation in the month change node and the biggest fluctuations occurred in July,but the overall change is relatively stable in the month.The same trend of the each pollutants dynamic water environment capacity of the control sections 1～7 and the intake water diversion project from the Yellow River to Huhhot of one to four layers.The dynamic water environmental capacity of each pollutants from upstream to downstream along the Yellow River at Huhhot is gradually reduced.The existing water intake point is the best water intake point on the existing water intake section.The best water point in the existing water intake section of the existing water point.Selecting the vertical simga second (1～2m) and third layers (2～3m) accordance with river characteristics and seasonal features in intake port.(5)The dynamic water environmental capacity risk value variation range of DO、 COD、BOD、NH3-N、TP、NO3-、FC of the Yellow River at Huhhot are 1.18～1.50、 1.33～2.19、1.03～1.6、0.04～2.53、0.87～1.60、0.40～0.79、0.24～1.34.1～4 layers dynamic water environmental capacity risk value variation range of DO、COD、BOD、 NH3-N、TP、NO3-、FC of the intake water diversion project from the Yellow River to Huhhot are 0.69～1.51、1.21 ～ 1.89.1.13～1.59、 0.45～1.76、0.90～1.30、0.42～0.82、 0.24～1.31.The water environmental risk of COD and NH3-N is at a low and middle leve, while the water environmental risk of DO, BOD, NO3-、 TP and FC is below the low level.(6)The main reduction pollutants are COD and NH3-N of the Yellow River at Huhhot. The date of COD reduction is from April 16th to May 17th and the total reduction amount is 4570.19t/a,maximum reduction amount is 57.52t/d.The date of NH3-N reduction is from May 26th to June 7th and the total reduction amount is 3410.45t/a,maximum reduction amount is 16.12t/d.The main reduction section is the control section 1(The intake water diversion project from the Yellow River to Huhhot).The dynamic water environment capacity of DO、COD、BOD、NH3-N、TP、NO3-、 FC of the Yellow River at Huhhot are considerable and at lower risk level, Short negative dynamic water environment capacity of COD and NH3-N.the Yellow River at Huhhot can health and sustainable development in total amount control and countermeasures forprotection, not to the intake water diversion project from the Yellow River to Huhhot caused by persistent effect.