Evaluation of reduction rate of rainwater runoff pollution load in low impact development community based on rainfall grade differentiation method

In order to quantitatively evaluate the reduction rate of low impact development (LID) techniques on rainwater runoff pollution load, Liuan Hefeng Community in Jiaxing City was selected as the LID community, and Bay Community adjacent to it with similar underlying surface types was selected as the traditional community. The external discharge and TP concentration of the communities were monitored simultaneously. Then, the pollution load per unit area of the two communities was calculated according to the rainfall level differentiation under the same rainfall situation. Finally, the reduction rate of rainwater runoff pollution load of LID community was calculated based on the pollution load of unit area of traditional community. The results showed that: In light rain, LID facilities absorbed all the runoff and pollutants within their service range, and achieved a 100% reduction rate of pollution load. With the increase of rainfall, runoff and pollutants carried by it gradually exceeded the functional threshold of LID facilities, and the pollutant abatement rate began to decrease. In moderate rain the reduction rate dropped to 67% and in heavy rain it dropped to 46%. The average annual reduction rate of rainwater runoff pollution load was about 66%. On the whole, the reduction rate of rainwater runoff pollution load of LID facilities showed obvious differences in rainfall levels. The method of rainfall level differentiation could reduce the error caused by rainfall levels and ensure the accuracy of evaluation results, which provided a reliable decision-making basis for LID facility construction in communities.