WITHDRAWN: Parameterizing Unit Hydrographs (UH) to account for Rainfall Derived Infiltration and Inflow (RDII) from different land use in tropical urban environments

Abstract

• Rainfall Derived Infiltration and Inflow of an urban tropical environment are parameterized for the first time. • 12 catchment models across Singapore were developed for our analyses. • The transient hydrometeorologic and seasonal factors were also evaluated. • Forests have the most delayed unit hydrographs. • Results provide practical guidelines for urban sewage engineers and modelers. Rainfall-derived infiltration and inflow (RDII), the subsurface flow that enters a drainage system during and sometimes long after cessation of rainfall, may negatively impact system performance and cost. Accounting for RDII, however, is subject to a number of uncertainties, of which land use land cover (LULC) constitutes a major factor. One of the options in the Stormwater Management Model (SWMM) to represent RDII is the triangular Unit Hydrograph (UH) approach where the UH shape is described by three parameters: R, T, and K. Literature parameterizing R T K is limited and predominantly associated with temperate climate areas. As such, this study examined tropical sub-catchments across Singapore, where the characterization of RDII is critical due to the heavy rainfalls and high-water table for the effective design of the drainage system. In total, we instrumented and modelled 12 sub-catchments at the district level, representing different LULC. The fit of the modelled flow was generally improved through explicit inclusion of the RDII in terms of the coefficient of determination R 2 (0.709-0.976) and Nash Sutcliffe Efficiency (NSE) (0.705-0.982) between observed and modelled flow. The calibrated UH parameters varied both temporally and spatially. In particular, the K values were greater for forested areas as compared to other LULC categories. Temporally, the R values were high and the most varied in July and August, while the T values were high in August, October, and November.. The values of the UH parameters derived from this research provide practical estimation guidelines for engineers and modellers that are involved in complex RDII problems.