Regionalisation of impervious area parameters of urban drainage models

Stormwater drainage models are increasingly being used in design and analysis of urban drainage systems. If these models are to be used for ungauged drainage systems for which no storm and corresponding flow data are available, then the model parameters have to be estimated through regional equations. These regional equations define the model parameters via measurable catchment properties. In this study, regional equations of two impervious area parameters, namely directly connected impervious area percentage (DCIA) and its depression storage (DSi ), were developed for use in urban drainage models, using 15 gauged urban catchments in Melbourne Metropolitan area (Australia). The ‘small’ storm events of these gauged catchments were first used to calibrate the impervious area parameters, since the ‘small’ storm events produce runoff only from the impervious areas. These calibrated impervious area model parameters were then analysed with several measurable catchment properties to derive the regional equations. The results of the study revealed that DCIA was depended only on household density of the catchment, while DSi was not correlated with any of the catchment properties analysed.