Over 6500 hectares of sea grass have been lost from Adelaide’s coastal waters since 1949. This has had a negative impact on the environmental, community and economic values associated with St Vincent Gulf. Excess nutrients and turbidity (cloudy water due to suspended particles) were identified as the main causes of this loss. Nutrient inputs have now been significantly reduced and so the primary barrier to sea grass restoration is the input of sediment, particularly fine sediment.
While we understand where fine sediments are coming from, we don’t know which types of urban water management interventions are best suited to help stop fine sediments reaching the Gulf. This project developed a decision support framework to help prioritise investment in urban stormwater water management interventions to reduce inputs of fine sediment to Adelaide’s coastal waters.
In developing the decision support framework, the team has:
• considered the effectiveness of different interventions, with a focus on known interventions rather than new interventions
• synthesised existing information on sources of fine sediment to the Gulf
• applied a multi-criteria assessment approach
• considered opportunities for co-investment across local and state government.
The framework was tested and applied at a sub-catchment scale in the first instance and is set up in a manner that allows it to be further refined and applied to all metropolitan Adelaide catchments in the future. The framework is intended to inform investment decisions by the South Australian Government.
The project was funded by the Department for Environment and Water as part of the New Life for our Coastal Environments program.
The project has produced a spreadsheet-based framework that can support state and local government decisions on where and how best to invest in urban water management solutions across Metropolitan Adelaide to remove fine sediment from stormwater runoff in the short-term. This was developed following consultation with government agency staff and a variety of local government representatives. It was tested in a number of sub-catchments around the Adelaide metropolitan area including: .
The framework considers key sources of fine sediment and appropriate interventions, and then determines the relative risk of a catchment for the generation of fine sediment. It can be used to assess one catchment but is more ideally suited to comparing the risks of several, where those with the highest weighted score are those with the highest risk for sediment export.
Beyond immediate use in supporting the prioritisation of investment into urban stormwater quality management interventions, the framework has also identified a number of data gaps and made several recommendations as to how to improve local understanding of fine sediment sources and measures to reduce sediment transport to Adelaide’s coastal waters. The key recommendations were: