Regional Council in New Zealand benefits from web-based geospatial decision support system

In New Zealand, stormwater runoff from urban catchments often end up in receiving water bodies such as streams, rivers, wetlands, estuaries and exposed ocean coastlines. When stormwater contacts surfaces like impermeable roofs, roads, carparks and so on, it carries significant amounts of contaminants into the receiving waters.

Environment Canterbury wanted to make it easier for local councils to assess the effectiveness of stormwater management options to reduce the impacts on receiving water quality. In collaboration with the University of Canterbury, DHI developed a GIS-based decision support system – ‘MEDUSA Online: Contaminant Loading On-Demand’.

Challenge

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. In order to manage stormwater effectively, Environment Canterbury needed a solution that would help them, and local councils who are responsible for stormwater networks, to quickly and easily identify critical pollution source areas so they can prioritise their efforts and mitigate impact through optimal measures.

Solution

To address the major aspects in managing stormwater quality, DHI developed ‘MEDUSA Online: Contaminant Loading On-Demand’. The web portal allows catchment managers to investigate catchment characteristics, quantify loads from individual surfaces, compute in-stream concentrations in the receiving waters, prioritise sub-catchments and simulate mitigation measures to determine the impact of green infrastructure on contaminant loading and concentration.

The system generates predictions of single-rain-event contaminant loads at the point of runoff from individual surfaces. Users can 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. With the simple interface, users can easily explore the effects of implementing different treatment systems (at source as well as end-of-the-pipe) at any site in the catchment.

Solution components

The solution integrates University of Canterbury’s MEDUSA (Modelled Estimates of Discharges for Urban Stormwater Assessment) engine with MIKE Powered by DHI software MIKE URBAN (now MIKE+). The integrated system estimates the amount of contaminants generated by individual surfaces within the catchment, based on local monitoring of different surface types. Features include the surface-specific load generation component, based on rainfall characteristics and the ability to couple with hydraulic models to translate into instream concentrations.