Abstract

In 1993 the City of Edmonton initiated a project to update existing SWMM2 RUNOFF and EXTRAN models of the 30th Avenue storm sewer system for the purpose of evaluating cost-effective solution strategies for upgrading the system. Part of the requirements for attaining this goal included simulating the major system operation to compute surface flooding locations, depths and frequencies. The 30th Avenue storm basin encompasses a total area of some 5,400 ha in south Edmonton. The vast majority of the basin’s major system does not follow a dendritic drainage pattern. Rather, surface runoff collects in localized street depressions before entering the storm sewer system. During intense rainfalls, localized ponding can cause temporary nuisance and flooding.

Three alternative methods were proposed to simulate both major and minor system storm drainage: modified SWMM modelling to simulate ponding at major system depressions; modelling with OTTHYMO 89; and modelling with PC OTTSWMM. Each model generates runoff data suitable for minor system routing with EXTRAN. Monitored rainfall and flow data was available for model calibration. Rainfall-runoff models were compared on performance against easured data and suitability for City requirements. A test catchment was proposed to determine which of the three methods was most appropriate for overall basin modelling. The 280 ha Knottwood Community in south west Mill Woods was selected because it represented a manageable size, contained over 50 major system depressions, comprised a representative mixed land use, was flow monitored and located close to a rain gage (Figure 23.1).

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