June 2006 Forum
Evolving science and management of stormwater, including constructed wetlands
The guest speaker was Mr Andrew Thomas, Project Manager, Adelaide and Mt Lofty Ranges Natural Resources Management Board, who gave a very informative presentation on 'Evolving Knowledge in Stormwater Management'. The forum was held on-site at Urrbrae Wetlands, and Dr Allin Hodson, Coordinator of the Urrbrae Wetlands Complex and speaker at the March forum, provided a tour of the site.
Andrew provided a very useful overview of the management issues and priorities in urbanized catchments, and described the 'treatment train' required to deal with the mixed components of stormwater on its journey through the catchment. It was startling to learn that the highly visible litter component in stormwater is only 10% of the pollutant volume, and that organic material (70%) and silt (20%) are the major components requiring treatment and management. Leaf litter is the largest problem in urban catchments, with street sweeping removing only a small proportion of the problem.
The ideal treatment train includes a combination of trash racks, sedimentation basin, litter boom and wetland filtration basin, with adequate capacity to allow sufficient residence time in the system before discharge downstream. Andrew pointed out the difficulties of retro-fitting existing systems which were installed without sufficient features to include all of these steps.
Andrew's comments reinforced the points raised by Allin Hodson about inefficiencies in stormwater management at the March forum, and the group was able to view on-site the extensions to the Urrbrae Wetland which are attempting to increase its flexibility and capacity within the constraints of available land, local flood risk and outflow capacity. The CSIRO aquifer storage and recovery project was also inspected, where trials are being conducted to find methods to prevent clogging by algal growth in fine sand aquifers so that stormwater can be stored effectively.
Postgraduate Young-Kil Kim also described his project, which is examining water quality issues in relation to stormwater management and re-use at the Parafield Wetlands, which the group visited during the December forum. Young-Kil is investigating several questions such as the relationship between the sediment and open water, and the effect of invading water plants on water quality, and anticipates making recommendations about residence time, plant harvesting and relative areas of open water for improved management of the wetlands.