Identification, Prioritization, and Mitigation – a Three Step Process for Stormwater Quality Management

Stormwater Conference

Development of effective plans for stormwater quality management to mitigate the degradation of freshwater quality in urban catchments demands an explicit understanding of the catchment both spatially and temporally. This includes “identification” of critical source areas for pollutant load reduction, “prioritization” based on contaminant influence on in-stream ecological health, and “mitigation” through optimal measures. To address these three major aspects of stormwater quality management, we developed an online geospatial decision support system called “MEDUSA Online: Contaminant Loading On Demand”.

This system allows catchment managers to investigate catchment characteristics, quantify loads from individual surfaces, compute in-stream concentrations in the receiving waters, prioritize sub-catchments, and simulate mitigation measures to determine impact of green infrastructure on loading and concentration. The system generates predictions of single-rain-event contaminant loads at the point of runoff from individual surfaces. The system allows users to identify the spatial distribution of contaminants as well as the relative contribution from the different surface types in the catchment at both event and annual timeframes. The system facilitates the user to explore the effects of implementing different treatment systems (surface as well as end-of-the-pipe) at any site in the catchment.

This system integrates University of Canterbury’s MEDUSA (Modelled Estimates of Discharges for Urban Stormwater Assessment) engine with MIKE Powered by DHI software. MEDUSA is an event-based contaminant load model that estimates the amount of contaminants generated by individual surfaces within the catchment. MIKE suite of software is used to model hydrological, hydrodynamic and water quality processes in the stormwater network as well as in the receiving environment. The integrated system enables the identification and prioritization of critical source areas for pollutant reduction and facilitates mitigation measures for optimal siting of LID measures in urban catchments. The web-based system is accessible to a wide range of users – including Regional Council, City Council, District Council, Consultants, Infrastructure developers, and Property owners.


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01 Oct 2019


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01 Oct 2019