Stormwater hydrographs from the highly urbanized catchment for synthetic rainfalls with linear patterns

Abstract

Rainfall intensity is a critical input factor in rainfall–runoff modelling. This study examines the impact of intensity irregularities on runoff hydrographs, focusing on synthetic rainfall events with linear variations in intensity at different rates. The effects of rainfall intensity parameters on stormwater hydrographs in a highly urbanized, fully impervious small square catchment for the climatic conditions of Lviv (Ukraine) are studied numerically using the stormwater management model program. Initial depression depths in the range of 0–5 mm, with corresponding Manning’s roughness coefficients from 0.01 to 0.018, are considered. The peak flow rates of resulting hydrographs consistently align with a dimensionless coefficient of linear intensity variability k' = +1, while the minimum values correspond to k' = 0.67. The maximum peak flow rates for the intensity coefficient of k' = +1 can be expressed as the product of the peak flow rate for a design rainfall event of constant intensity and the generalized adjustment factor Ktot, which shows a clear linear correlation with depression depth. The findings of this study offer new insights into stormwater runoff behaviour under varying rainfall intensities, providing valuable information for urban water management and flood risk assessment in highly impervious urban catchments.