Risk Assessment of Upper-Middle Reaches of Luanhe River Basin in Sudden Water Pollution Incidents Based on Control Units of Water Function Areas

Upper-middle reaches of Luanhe River Basin belongs to Haihe River Basin and it is a pretty important water source to North China, especially to Tianjin and Tangshan Cities, Hebei. Based on control units of the water function areas and the sub-basins the working units were produced. The index system for environmental risk source hazard was constructed by adopting the pressure state response (PSR) environmental analysis model. The environment risk sources are identified, and their hazard grade assessment is performed. In the environmental risk source hazard an assessment index system, namely “downstream characteristics of environmental risk sources” is added by taking the fact into account that environmental risk sources themselves are affected by different functional areas (working units) downstream of the rivers. Through collecting hazard data, determining their standards and weights for environment risk sources, the fuzzy comprehensive evaluation method is used to calculate the risk source hazard grades and the vulnerability grades of the working units. Using the one-dimensional exponential decay river model for pollutants in rivers, the hazard grade evaluation method of working units is established. This consists of two parts: (1) The risk source hazard grade of the working unit itself, and (2) the impact of the risk sources upstream on the working unit downstream of the rivers. Combining the hazard grade with the vulnerability grade of the working unit, the risk grade of the working unit is evaluated through the risk matrix. The risk zones of the watershed are realized by merging working units in the same control units of the water function areas with the same risk grades. The risk zoning of sudden water pollution incidents in the upper and middle reaches of Luanhe River Basin is obtained by applying the above risk zoning method. It is found that there are 55 risk zones in total, including three highest risk zones, 15 higher risk zones, 14 lower risk zones, 23 lowest risk zones. These results indicate that the upper and middle reaches of River Luanhe are overall at low risk. The corresponding management methods for the different risk zones are suggested