How does flow connection path and vertical spatial layout of LIDs affect urban runoff? A new LID construction method based on refined landuse and hydrologic characterization

The techniques and modeling methods of Low Impact Development (LID, a more decentralized approach that uses or mimics natural processes to mange stormwater), has been extensively studied due to their positive impacts on urban flooding and water environment. Traditional LID modeling has been typically allocated on a plane layout based on rough land use classification and hydrological characterization. As the LIDs cannot be combined in the same space due to modeling restrictions, the LID effects on runoff control are often underestimated. This paper proposed a vertical LID model construction method based on a refined land use classification and improved hydrological characterization. By establishing a flow connection flux in the LID controller calculations, the overflows of different LIDs can be interconnected and transferred for further infiltration, storage and conveyance. Results showed that the refined approach provided more accurate spatial allocation guidance for LIDs, and the obtained catchment outflow was reduced by 25%-34% in comparison to conventional land use classification in a case study in northern China. The vertical construction method allowed a multi-dimensional LID allocation in space and function and achieved a higher control effect on total outflow volume and peak value. The combined LIDs could cope with the rainfall (i.e., no outflow from the LID plots) within the 50-year event, and the total outflow volume was 13-26% lower than the one from the plane layout method.