Stormwater Drain Blocked? What Sydney Homeowners Need to Know

Your driveway has recurrent flooding during rainfall. There is water against the house. The garden is becoming like a swamp! These are issues related to stormwater, they’re nothing like sewer backups.

When most people in Sydney hear the words “blocked drains” they imagine a sewer issue, spilling toilets, showers overflowing and sewage backing up onto the lawn. However, storm water drains are a totally different system and blockages result in flooding, erosion, damage to the foundation and water coming from the outside of the home.

Stormwater drains capture the rainwater/stormwater that drains from your roof (through gutters and downpipes), from driveways, paths and garden areas and deliver it into stormwater drains to the council or Sydney Water stormwater system which ends up in creeks or harbours or the ocean. These are clean(ish) rainwater streams that are drained into the stormwater system. Sewer system is for transporting wastewater from toilets, sinks and showers. These are totally different systems in modern-day Sydney properties. Decades ago, legacy combined systems once conveyed both, and remain so in some older areas (especially Rushcutters Bay, Darlinghurst and some locations in the inner west).

What Stops Storm Water Drains

Falls, leaf litter and garden debris. This is the most usual reason, particularly during the fall. Downpipes, pits and grates on the streets capture leaves, bark, twigs, and grass clippings that are washed off of garden beds and lawns. Debris will cause a partially blocked stormwater pit to become overflow after a few weeks of debris built up and a single heavy rain.

Tree roots. The reason for terracotta (and PVC) sewer lines to have this root problem also applies to stormwater pipes, meaning that PVC stormwater drains with deteriorated joints and cracked terracotta stormwater drains are equally vulnerable to root entry. Those same processes start in storm water pipes, but at a slower rate, because the storm water pipes do not entrap as much of the warm nutrient-rich contents that sewer pipes do, but the outcome is the same — a line that does not flow when the storm hits.

Silt and sediment. Over time, the small soil particles erode into the stormwater pits and deposit in the pipe. Sediment in stormwater pipes is an ongoing problem in Sydney’s Eastern Suburbs where the soils are sandy and found closer to the coast. Over time the pipe deposits dirt and until it collects too much, it becomes incapable of achieving peak flows.

Construction debris. Neighbouring buildings undergoing renovations or construction may add sand, cement, brick pieces and packaging material to the storm water system. If the storm water issues occur at the same time as construction in the area, then there could be a relationship between the two.

Who's Responsible for Stormwater Drains

On your property Your responsibility. All stormwater drainage on your property, such as the gutters, downpipes, sub-surface drains, pits and pipes are the private property of you, the homeowner. As the owner of the property, you are responsible for maintaining and clearing them.

Council’s stormwater system: Your local council is responsible for monitoring and maintaining the kerb and gutter system, and the smaller stormwater pipes that link this system to the larger network. Notify your council when stormwater is flooding from a council pit, grate or street pipe.

Sydney Water manages these larger stormwater mains, channels and outfalls, referred to as trunk drainage in Sydney Water. Many catchments have specific ‘handover’ points where the council’s minor system links with Sydney Water’s trunk system.

Red flags for blocked stormwater drain include:

The problem of water accumulating on the driveway or footpath when it rains. If water has suddenly begun to pool for several hours that previously drained quickly, then it is likely that the stormwater pipe or pit beneath it is clogged.

During the rain water runs up the garden grate. The downstream pipe is unable to pass the flow causing the pit below the grate to surcharge. There’s a blockage downstream.

Wet or wet marks on the house lower wall. When rain can not be drained away from the structure, it accumulates around the foundation, which can cause infiltration of stormwater through cracks in the slab/masonry.

Garden erosion. Runoff of water in places it does not belong, such as erosion of soil, washout of containers and beds or pathway gully erosion across the lawn, can signal that the stormwater system is not collecting and directing runoff as was intended.

The Problem is Storm Season

Sydney stormwater blockages are a seasonal occurrence. They grow incrementally when it’s dry (leaves fall and attach, silt settles, root growth continues) and then pose a problem when it rains for the first time, in big volume. The light showers weren’t causing any issues for the system, but, when it comes to a heavy east coast low dumping 50mm in an hour, the partially blocked pipe can’t handle it and the overflow appears as flooding.

for this reason, annual stormwater maintenance (clearing stormwater pits, flushing pipes, and checking for root intrusion) is prudent, and preferable, to be done prior to the storm season since responding after flooding has occurred. An ounce of prevention in the fall can save you money from a call out after your garage is flooded due to a storm situation.

With all the excitement and passion about the waterfront, nobody wants to think about stormwater maintenance. Stormwater drains are not thought of until the driveway is flooded. However, by capping the annual pit clean and pipe flush cost with $250 – $500, one can avoid this scenario just fine. Now is the time, before autumn storms, or else on a Saturday night with water lapping at your garage door.