Sustainable Stormwater Management: Runoff Impact of Urban Land Layout with Multi-Level Impervious Surface Coverage

The expansion of urban impervious surfaces exacerbates flooding risks, influenced by both impervious surface coverage (ISC) and its spatial distribution. To investigate the impact of urban land use layouts on stormwater runoff, this study examined the current land use conditions in the Xinling Bay watershed of Xiamen, China, and generalized land use into three ISC classes: impervious (I, ISC = 100%), semi-pervious (S, ISC = 50%), and pervious (P, ISC = 0%). Six spatial layouts (ISP, IPS, SIP, PIS, SPI, and PSI) were modeled using SWMM under varying rainfall intensities and land unit scales. The influence of ISC layouts on peak runoff, peak time, and total runoff was simulated. The results indicate: (1) The IPS spatial layout yields the most effective stormwater mitigation; (2) Prioritizing impervious land upstream while avoiding pervious units upstream minimizes runoff; (3) Layout effects weaken with higher rainfall intensity but strengthen with larger scales. These findings provide actionable strategies for sustainable urban planning to enhance flood resilience through spatial distribution optimization.