Critical source areas identification and reduction plan of non-point source pollution in a typical community in a plain river network city, China

Increasing non-point source pollution (NSP) due to population growth and urbanization has caused the deterioration of urban water environments, and the characteristics of stagnant water flow and complex river channels in plain river network areas have hindered the prevention and management of NSP there. Therefore, the simulation of NSP, the identification of critical source areas and proposal of effective pollution reduction schemes for the plain river network areas can contribute to the sustainable development of the natural ecology and social economy of plain river network areas. This study takes the Xinlong pilot area in Changzhou city as the study area. A NSP critical area identification system based on the PCSWMM model results was constructed for the characteristics of the plain river network city. Nine low-impact development construction scenarios based on three LID facilities were developed for the identified critical area, and the peak runoff reduction, pipe network overflow reduction and COD, TN and TSS load reduction were analyzed for each scenario under five rainfall recurrence periods of 5a, 10a, 30a, 50a, and 100a. The main findings of this study are as follows: 1) NSP The critical areas are old residential areas; 2) Scenario 2, which includes higher proportion of green roof and rain garden, shows best performance for peak runoff reduction, achieving a reduction rate of 11.19 %, 11.02 %, 10.75 %, 10.63 %, and 10.59 % under five rainfall recurrences, respectively; and 3) Among the nine renovation scenarios, scheme 8, which allocates 3 % to green roof, 2 % to permeable pavement, and 4 % to rain garden, demonstrated relatively good performance in simultaneously achieving runoff reduction, pipe network overflow rate reduction, and pollutant load reduction. The methods and results of this study provided improvements and guidance for urban planners and environmental managers in designing more effective and sustainable NSP control measures in plain river network cities.