Hobsons Bay City Council - Stormwater and waterways

Stormwater and waterways

Stormwater and waterways

Learn more about stormwater, how it impacts our waterways and what you can do to help improve water quality.

In this section:

Pollutants in Stormwater
Urban Catchments
Water Sensitive Urban Design


Stormwater is the runoff we get when it rains. Water falling on solid surfaces — including roofs, roads and paths — runs off the surfaces and becomes stormwater. Stormwater is collected in stormwater drains in the street. It’s channelled, untreated, straight into local waterways or Port Phillip Bay.

Our waterways need water however stormwater can also be a threat to their health. Stormwater picks up many pollutants. The biggest impact comes from buildings, roads and pavements decreasing waterways’ dry weather flows and increase the risk of flooding. Read the following sections for more detail on the impacts and how you can help manage these potential issues.

Pollutants in stormwater


Rainwater picks up many pollutants before it reaches the drain. The most well-known and visible of these is litter. Litter from our streets is swept straight into the drainage system when it rains. Litter makes our waterways look ugly and can kill local wild life. Plastic bags, plastic six-pack rings and discarded fishing line can entangle and strangle wildlife. For information on how you can reduce litter see Council’s litter page.


Pathogens are microorganisms that cause illnesses. They include viruses and bacteria including E. coli. E. coli gets into our waterways and bays from dog faeces that have not been disposed of correctly. E. coli can also come from illegal stormwater connections—for example, when someone mistakenly connects their sewerage system to the stormwater drain instead of the sewer. For sewer or drainage connections always use a licensed plumber. Check here for dog off-leash locations in Hobsons Bay.


Toxins cause illness at a given concentration—they include heavy metals found in paint or rust. Petroleum products such as motor oil contain toxins as do pesticides and herbicides. These products should not be allowed to run into the drain. For information on how to safely dispose of products go to the Resource Smart website.


Nutrients such as nitrogen and phosphorus are found in food scraps and fertilizers. Plants love these nutrients and they help them grow. However, algae are plants and they love nutrients too. Keeping fertilizers and food scraps well away from drains will help prevent algae blooms in our waterways and the Bay.

Suspended solids

Fine particles including dust from construction sites collect in our streets and wash into drains and waterways when it rains. When it rains the speed of the waterway is too slow to move the sediment and it smothers everything that lives and grows on the river bed. It takes a high rainfall event to move the water fast enough to move the sediment and deposit it on the banks where plants can grow. To stop sediment blocking waterways in rainfall events follow these EPA guidelines.

Urban Catchments

An urban catchment is a developed area with roads and drainage pipes. 

When it rains in an undeveloped area some water flows overland and into local waterways while the rest seeps into the ground. Water that seeps into the ground fills up the water table, gets taken up by plants and trickles into streams producing dry weather flows.

In urban catchments, the ground is covered with hard surfaces and water is quickly channelled away through stormwater drains. Less water seeps into the ground and into streams during the dryer months.

The water channelled through stormwater drains creates a sudden high flow in waterways for a short period of time. 


Diagram of urban catchment - described above. The rainfall is Precipitation, the water seeping through the ground is Infiltration, the water moving from the ground back into the air is Transpiration and Evaporation and the flow from the underground water table into the catchment is Base Flow.

Water Sensitive Urban Design (WSUD) is a way of mimicking the natural water cycle and restoring the health of our waterways.

Water Sensitive Urban Design

Water Sensitive Urban Design (WSUD) applies water cycle management, protection and conservation measures in urban areas. This includes:

  • slowing down the flow of water;
  • enabling water to soak into the ground;

  • removing excess stormwater from the stormwater system; and

  • filtering the water.

Slowing down the flow of water reduces the highest (peak) flows. It also means that stormwater flows through the waterway for longer. Swales (open grassy drains), raingardens and wetlands all slow down the flow of water.

Enabling water to soak into the ground recharges the groundwater. It also means more water is available to plants, reducing the need for watering. Swales and raingardens help water to soak into the ground.

Removing excess stormwater from the system reduces peak flows. Rainwater tanks can store excess stormwater so it doesn’t go into the stormwater system. However, tanks must not be full when it starts to rain as they won’t be able to catch the excess stormwater. Connecting your rainwater tank to the toilet and washing machine means that you use stored rainwater constantly and there will be enough room in the tank for it to capture excess stormwater. The connection to the toilet and laundry should be accessible and easy to turn on and off so that you have good control over when and where you use tank or tap water.

Filtering pollutants out of the stormwater system improves the quality of waterways for fish and other aquatic species. Pollutants such as sediment and nutrients can be filtered out of the stormwater by swales, raingardens and wetlands.

Residents - How to build a raingarden Melbournewater.com.au.

New developments - How to use Water Sensitive Urban Design in your development Melbournewater.com.au.

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