Influence of rainfall dynamics uncertainty on sensitivity analyses results in hydrodynamic models of large urbanised catchments

Abstract

Abstract This paper presents an analysis method of rainfall uncertainty influence on the variability of modelled runoff from a municipal catchment. The model of 41.75 km2 basin prepared in SWMM 5.0 software was used in this study. The developed model consisted of 120 sub-catchments of area 5-100 ha and terrain slope 0.2 – 6%. The share of the impervious surface area of sub-catchments was in the range of 1 – 80%. The model was preliminary calibrated basing on measurement data for six rainfall-runoff events at four measuring cross-sections. To allow assessment of time-related rainfall intensity variability influence on maximal flow values registered at measuring cross-sections, the length of time step was changed by a division of registered data values on 30 minutes periods. The uncertainty parameterisation was performed for analysed rainfall events (resolution 30 minutes) by introduction the subsequent values of θ = {0.3; 0.4; 0.5; 0.6; 0.7}. Thus, it was assumed that for θ = 0.3, 30% of hourly rainfall dropped during the first 30 minutes, the remaining 70% during the next time step, etc. For the assumed θ = 0.3 – 0.7 values influence calculations of calibrated parameters variability (retention depth of impervious, impervious surfaces, the roughness of impervious surfaces, retention depth of pervious surfaces, and roughness of pervious surfaces) on modelled values of maximal flows at measuring cross-sections were performed. In order to supplement the analysis, the influence of impervious terrains spatial variability at measuring cross-sections on determined dynamics of maximal flows concerning SWMM 5.0 calibrated parameter values was assessed.