A joint risk assessment method of waterlogging and non-point source pollution in urban built-up areas

Waterlogging and non-point source pollution are two common problems in urban built-up areas, both of which are closely related to the rainfall runoff process, forming a risk superposition.In order to systematically evaluate the risk of waterlogging and non-point source pollution in urban built-up areas, a joint risk assessment method was proposed which based on the established water quantity-water quality joint risk assessment index, as well as Copula joint distribution function and SWMM-InfoWorks ICM coupling model.A university is used as the research area, in which a comparative analysis of two different gray-green scenarios is carried out.The results show that: compared with the baseline scenario, the average values of waterlogging control elasticity, runoff control elasticity, and water quality control elasticity in the built-up area under the renovation scenario increased from 0.55, 0.90, and 0.76 to 0.63, 0.95, and 0.80, respectively.However, while the degree of risk decreased, waterlogging and water quality exceeding the standard still existed at the same time.In addition, extreme points exist in the probability density distribution of water quality elasticity values under two scenarios, which are mainly caused by the reduction of SS control ability.In multiple rainfall events been recorded, the high-low risk boundary return period of water quantity and water quality increased from 2.21 a and 1.60 a to 4.59 a and 1.81 a, respectively, which means the risk probability decreased.At last, after the gray-green transformation, the water quantity control ability increased but the water quality control ability decreased, indicating that the joint regulation of water quantity and water quality is very important.