The drainage system minimises the impact of flooding by safely carrying stormwater away from built-up areas into rivers and creeks.
What makes up the drainage system?
- 1,400 kilometres of regional drains, managed by Melbourne Water
- 25,000 kilometres of local drains and street gutters, managed by local councils
- residential roof gutters, downpipes and pipelines, which are the responsibility of property owners
- other drains managed by agencies like VicRoads and VicTrack
How the drainage system works
When it rains, some water naturally seeps into the ground. To prevent the rest of it from flowing towards low-lying land, the drainage system directs it into rivers and creeks — and eventually into the bay.
- Stormwater enters house gutters and downpipes, and flows into residential drains
- Residential drains connect to council drains along streets and roads
- Council drains connect to Melbourne Water’s regional drains
- Regional drains direct stormwater into the nearest river or creek, or directly to the bay via piped beach outlets
- Rivers and creeks flow into Port Phillip or Western Port bay
Drainage design standards
While it’s impossible to design a drainage system that can prevent all floods, under today’s standards:
- underground drainage systems can generally cope with frequent storms that have a 20% chance of occurring each year
- overland flow paths carry excess floodwater away from properties, preventing flooding during storms with up a 1% chance of occurring each year
- other benefits to waterways are considered, such as litter traps, stormwater treatment wetlands and stormwater harvesting
Stormwater beach outlets: sand scouring
Some stormwater from piped beach outlets can leave uneven areas of sand due to the exiting water’s volume and force. This is called sand scouring, and while it also happens naturally from wind and waves, we are committed to working with the community to reduce its impact.
Entering stormwater drains is illegal, dangerous and in some cases, fatal. Conditions inside a drain can change quickly without warning:
- water levels can rise or suddenly arrive from kilometres away, even on a sunny day
- slow moving flows can become raging torrents
- poisonous gases and low oxygen areas can be deadly
- steep, hidden slopes are easy to slip on and can prevent others from hearing you call for help
We can’t cover all stormwater drains and grilles — this would restrict water flow and make litter and debris build up, causing flooding. Warning signs are placed at drain across Melbourne.