Research On Water Environment Capacity Of Han River(Shaanxi Section)

Water environmental capacity is the basis and gist for rationally planning water resources.With the development of industry and urbanization,water pollution problem has becoming more and more serious.In order to make rational and effective use of water resources for social and economic construction,water environmental capacity needs to be evaluated in order to provide surpport for environmental management.Through investigation and analysis of water quality,economy and ecology in the upper reaches of the Han River(Shaanxi section),COD(chemical oxygen demand)is identified as the main pollution factor in this study area.Several different water quality models and methods were compared.Moreover,the river's bed roughness and COD degradation coefficient of Han River Ankang section was calibrated using MIKE software.The relationship between the unevenness coefficient and the flow rate,pollutant degradation coefficient and river width was studied.This paper analyzes the shortcomings of the traditional one-dimensional water environmental capacity calculation formula,and modifies the calculation formula from two aspects:unevenness coefficient and water quality standard rate.The main conclusion of the study are as follows:(1)Through study,The value of the unevenness coefficient is related to the flow velocity,degradation coefficient,river width,distance from the upstream section of the sewage outlet,and the proportion of the length of the discharge river to the total length of the river.The values of the inhomogeneous coefficient corresponding to river,middle river and river are between 0.8?1.0,0.4?0.8 and 0.1?0.4 respectively.(2)In this paper,we used MIKE21 hydrodynamic model for the simulation of the Han River Ankang section.The unstructured mesh being used was generated in MIKE21 software.The finite element method was adopted during the simulation.Finally,the simulation results shows that the roughness value of Ankang section n is betwwen 0.028 and 0.03.The COD degradation coefficient k is equal to 0.1/d and 0.175/d in the dry warter period and the water level period,respectively.The COD degradation coefficient k is equal to 0.18/d in the wet warter period.These three values satisfy the requirement of relevant specification.(3)In this paper,the traditional one-dimensional water environmental capacity formula is modified by introducing the inhomogeneous coefficient and water quality standard rate.The selected unevenness coefficient and the water quality standard rate were 0.8 and 0.5 respectively,and the calculated results were 85.4%of the traditional calculation results.(4)There are 13 functional areas whose pollution need to be cut during the dry water period and 7 functional areas whose pollution need to be cut during the level water period.On the otherhand,due to the Abundant river flow during wet water period,almost all functional areas could appropriately increased emissions.The amount of emissions that can be increased is about 258624.40 t/a respectively.