Keeping our drains flowing

In the central area of Cairns alone, there are 20,000m of culverts, 58,000m of open drains, 168,500m of pipes and 3,800m of waterways that require maintenance. This information provides an overview of drainage management in Cairns and surrounding areas: what Council does to maintain and improve drainage, major flood mitigation works, and what you can do to be prepared ahead of the wet season.

Annual drainage maintenance and cleaning program: Council maintains over 260 drains and waterways, many of which are tidal. Annual inspections are carried out on most drains prior to the wet season to identify any flow capacity issues and drains are cleaned if required. The capacity of drains can be significantly restricted by the invasion of vegetation, including mangroves. As mangroves provide fish habitat, there are limitations as to how tidal drains can be maintained. Council’s Marine Plant Management Strategy, endorsed by the Department of Agriculture, Fisheries and Forestry, sets out how drain capacity is best maintained. Council can only dredge unlined drains between April and October due to fish breeding seasons.

Emergency works: In addition to scheduled annual maintenance and cleaning, Council’s Investigations Unit responds to unforeseen drainage issues as the result of extreme weather events and arranges for improvement works to be carried out. Hearing local knowledge and first hand experiences helps to plan for future drainage improvements.

Did you know?
  • Council spends on average $5 million per year on drainage maintenance.
  • Pressure cleaning of the central Cairns underground drainage network costs $200 000 per annum.
  • It costs an average of $250 per metre to clean major drains of sediment—nearly half the overall cost of the annual drainage program is associated with dumping that acid sulphate soil appropriately.
  • Around 500 calls are received each year requesting assistance with drainage problems within central Cairns suburbs.
  • Each month, about 20 to 30 shopping trolleys are retrieved from the central drainage system in Cairns.
  • During and after periods of intense rainfall, work crews check 127 sites within central Cairns suburbs to make sure that grates are not blocked from debris being washed into the waterway systems from the surrounding hill slopes and properties.
  • There are 185 gross pollutant traps (GPTs) in waterways around the region that catch litter and debris before it reaches the ocean—each one requires regular cleaning.

What are tide gates? Installed at the sea‐facing end of a stormwater pipeline or waterway, tide gates can be hinged at the top allowing stormwater to pass freely into the ocean or creek. There are three sets of tide gates in central Cairns waterways and these are lowered into the waterway when very high tides (king tides) are forecast. As the tide height increases, tidal water pushes against the flap sealing it tightly and stopping saltwater from flooding low‐lying areas of land. They are never locked into place but can always move in a downstream direction (ie. towards the ocean). When stormwater levels are higher than tidal water levels, they open wider allowing stormwater to flow to the ocean.

CBD Flood Mitigation Scheme: This Scheme is part of a strategy which is aimed at reducing the impact of king tides and heavy rainfall on business and property in the CBD. During severe weather events, the underground pump station in Lake Street can move five cubic metres of stormwater per second into Trinity Inlet, which equates to a 1 in 100 year storm event. This major project has been undertaken in stages including:

  • $9 million Lake St pump station and associated drainage upgrades in Hartley and Wharf Sts (2009);
  • $1.5 million Wharf St improvements (2011).

Additional stages will be carried out subject to funding.

What can you do to help? If you live near a drainage easement, property owners should be aware that they may be held liable for damage caused by an illegal obstruction in an easement or drain. Therefore your assistance in checking and clearing any obstructions is appreciated. If you want to report drainage problems, please call Council’s customer service team on 1300 69 22 47 or log your feedback online.

Last updated: 26 June 2020