As stormwater makes its way to the Derwent, it picks up litter, sediment, fertiliser, bacteria and other pollutants that can harm wildlife and pollute our waterways. Furthermore, increased urbanisation results in larger volumes of run-off that may cause downstream flooding. Construction sites, roads, car parks, sports ovals and golf courses, and commercial and industrial sites are all contributors to stormwater contamination. In some areas, cross-connections between stormwater and sewerage systems are also a problem.
Stormwater runoff has been identified as a major source of pollution to the Derwent estuary, particularly with respect to litter, faecal bacteria and sediments. Regional stormwater monitoring programs have found that levels of some pollutants regularly exceed national water quality guidelines, and in some cases may result in beach closures after heavy rain.
The Derwent Estuary Program’s stormwater program has supported a number of initiatives to improve stormwater quality, including:
- Hosting regular stormwater meetings with regional councils
- Monitoring and modelling stormwater quality
- Developing a range of stormwater resources for local government and developers, including technical guidelines for Water Sensitive Urban Design
- Securing grant funding and supporting construction of stormwater treatment systems, including passive treatment wetlands at Windermere Bay and Whitewater Creek
- Developing Soil and Water Management guidelines for building and construction sites, and supporting their implementation
Pollution source tracking
To assist local councils with how to go about finding sources of pollution in their stormwater systems, the Derwent Estuary Program and partners in 2020 developed the Source Tracking Framework and Toolkit. The Framework outlines a standard process for identifying sources of faecal pollution in the Derwent estuary (at the beach) and in its sub-catchments (in the stormwater network). This process assists councils in developing and implementing strategic and targeted investigations in response to poor recreational water quality at swimming beaches. The Toolkit details a range of tools and methods that can be employed in source tracking investigations. One of these tools is the ammonia kit, a cheap and fast method that has already proven itself very effective in local Derwent estuary stormwater investigations.
Sediment and erosion control
Sediment generated from soil erosion on building and construction sites can be a major source of pollution to local waterways. In fact, a single building block can lose four truckloads of soil in one storm. Any sediment that moves off-site typically enters stormwater drains, clogging the stormwater system and transporting attached pollutants including nutrients, heavy metals and hydrocarbons into local waterways. Excessive sediment can kill fish and aquatic plants, silt up streams, and block stormwater pipes, which can lead to increased flooding.
The building and construction industry is responsible for soil and water management throughout all phases of a development. The soil and water management guidelines discussed in the Fact Sheets minimise erosion and sediment run-off from building sites. Benefits include:
- Greater compliance with the appropriate regulations including state environmental laws, thereby reducing the risk of fines and other penalties.
- Improved wet weather working conditions, reduced downtime and earlier building completion.
- Fewer public complaints and a better public image for businesses.
- Reduced stockpile losses and clean up costs.
- Healthier waterways and a cleaner environment for everyone.
Soil and water management on building and construction sites
- Large building and construction sites
- Standard building and construction sites
- Management plans
- Dispersive soils
- Minimise soil disturbance
- Preserve vegetation
- Divert up-slope water
- Erosion control mats and blankets
- Protect service trenches and stockpiles
- Early roof drainage connection
- Scour protection
- Stabilised site access
- Wheel wash
- Sediment fences and fibre rolls
- Protection of stormwater pits
- Protected concrete, brick and tile cutting
- Sediment basins
- Dust control
- Site revegetation