Unsafe Factors In Methods Of River Environmental Capacity Calculation

As one of the most important environmental management systems, total quantity control of water pollutants can effectively promote reduction of water pollutants and improve the environmental quality. Water environmental capacity is part of the theoretic base of total quantity control and right calculation method for water environmental capacity is dispensable.The paper reviews the development progress of study and application on water environmental capacity, points out problems, and proposes a prospect on its development in the future. The paper summarizes water quality models and calculation methods for water environmental capacity, including zero-dimension, one-dimension and two-dimension. Based on giving attention to the external orderliness of water quality simulation and the practical requirement of environmental management, the paper identifies and avoids the unsafe factor in capacity calculation, and brings forward reasonable calculation method by using some mathematical theories, such as differential and integral.The paper draws conclusions as follows. The unsafe factor in capacity calculation mostly is that the practical requirement of environmental management is not satisfied enough. The initial hypothesis condition of centralized discharge by one pollution outlet is more fit for capacity calculation than initial hypothesis condition of decentralized discharge by many pollution outlets; to amend the unsafe factor that not all water affects the dilution and reduction of the pollutant drained into wide river, the paper computes unsafe coefficient(0～1, mainly depending on width and ratio of width and length) to amend the initial calculation result of zero-dimension and one-dimension calculation; to amend the unsafe factor of pollutant density standard-exceeding along the entire reach and the oversized extent of pollutant density standard-exceeding at the pollution outlet cross section, which are made by simulating the pollutant density at first-section under the condition that the pollutant density is according with water quality standard at last-section, the paper proposed reasonable calculation method on the basis of some parameters, such as designed water quality achievable percentage(0.6 required) which is computed on the basis of the average pollutant concentration along the river is just achievable, designed water quality standard-exceeding extent and designed calculation segment length of reach which is computed on the basis of the dilution degree at the pollution outlet cross section is just achievable; to amend the unsafe factor that the pollutant mixing zone is lack of criterion, the paper proposed the allowable area of single mixing zone(1/3 of river width and 1200 meters of river length required), and proposed the allowable area of all mixing zone(35% length of whole river length required) , and put forward reasonable calculation method on the basis of capacity using extent is ruled.As the example, capacity of three reaches are analyzed and calculated, and it turns out to be very effective.In view of the systematical research on unsafe factors of capacity calculation, the work of this paper could provide us some reference in calculating the water environmental capacity across large region.