Stormwater

As stormwater flows to the Derwent, it picks up litter, sediment, fertiliser, bacteria and other pollutants that harm our waterways and estuary ecosystems.  Increased urbanisation - mainly increasing 'impervious surfaces' (sealed over ground) with buildings and roads - creates larger volumes and higher speeds of run-off.  This results in erosion, pollution and flooding. Construction sites, roads, car parks, sports ovals and golf courses, and commercial and industrial sites are all contributors to stormwater contamination. 

Pollution of the estuary from stormwater comes from things like:

·       Litter from shopping centres, fast food outlets, and wheelie bins;

·       Sediment and cement from construction sites;

·       Hydrocarbon pollution from vehicle fuel (also from the wearing out of tyres and brakes);

·       Heavy metals from commercial and industrial sites;

·       Bacteria and pathogens from cross-connections with sewer, and sewerage systems overflowing;

·       Dog poo (dog poo bags blocking the pipes are a problem too); and

·       Nitrogen over-fertilising lawns, sports ovals and golf courses.

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  works hard  to improve stormwater quality. This work includes:

• Raising awareness about the impacts of stormwater on our urban waterways and ultimately the Derwent Estuary;
• Running training and workshops to build stormwater management capacity with industry and Councils;
• Hosting regular stormwater meetings with regional councils;
• Monitoring stormwater quality;
• Providing stormwater management resources for local government and the construction industry, including the new (2023) Sediment and Erosion Control Fundamentals;
• Supporting builders, developers, civil contractors and home owners to get their site right when developing or renovating to prevent any water pollution;
• Securing grant funding and supporting construction of stormwater treatment systems, including passive treatment wetlands at Windermere Bay and Whitewater Creek;
• Providing the technical guidelines for Water Sensitive Urban Design; and
• The Tasmanian Stormwater Policy Guidance and Standards for Development (the TSPGD).

Erosion and Sediment Control

Sediment generated from soil erosion on building and construction sites is 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 Erosion and Sediment Fundamentals 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; and
• Healthier waterways and a cleaner environment for everyone.

 

(Click on above image to open document.)

The Tasmanian Stormwater Policy Guidance and Standards for Development (the TSPGD)

The DEP facilitated the Stormwater in Developments Working Group in 2021 to create a TSPGD policy guidance document to bring together stormwater requirements for the planning process for streamlined stormwater management in Tasmania.  The policy guidance document is being used by Councils as Planning Authorities to develop effective stormwater controls as they transition to the Tasmanian Planning Scheme  which has no Stormwater Code (as the interim schemes did).  The document is presented in two parts - Part 1 outlines the why of stormwater management  and Part 2 the practicalities of  how to implement stormwater management. 

 

Pollution source tracking

To assist Councils with how to find sources of pollution in their stormwater systems, in 2020 the Derwent Estuary Program and partners 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 to develop and implement strategic and targeted investigations in response to poor recreational water quality at swimming beaches, and impacting natural ecosystems. The Toolkit provides tools and methods for source tracking investigations. One of these tools is the ammonia kit - a cheap and fast method (5 minutes, on site!) showing if this is elevated nitrogen that can be used to follow pollution up into a catchment to the source

Source Tracking Framework and the Toolkit