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Outflow litter traps

Updated: Jun 6, 2022

Did you know that a lot of marine debris gets into the sea via storm drains? In this post I’ll describe some ways to prevent this happening. It’s something we definitely could campaign for on Bribie Island to help keep Pumicestone Passage clean.

Credit: Insidewaste

We are all familiar with this picture; plastic bottles, straws, bottle tops, bags, and other pollution littering our beaches and water ways. Apart from the obvious, reducing the amount of plastic produced, we need to find ways of reducing the amount of litter ending up in the environment.


This blog post looks at one method, traps placed at storm water outlets that are designed to capture large pieces of litter washed down storm water drains during periods of heavy rain before it can reach the waterways and oceans.


I first came across this method when I lived in Bowral in NSW. My neighbour and I were instrumental in forming a local landcare group with the express purpose of cleaning up the creek running behind his house. To cut a long story short the creek was cleaned up, various flood mitigation methods put in place by council and we then replanted the banks with native trees, shrubs and grasses.. The creek still floods but less severely (at least until this years floods) and, importantly the water now drains away a lot faster.


As part of the work carried out by council various “gross pollution traps” were installed along the creek at storm water outlets and these were successful in reducing the amount of litter entering the creek and as the creek was in the Sydney catchment area this was important work.


Examples of Gross Pollution Traps


So let's look at some forms of gross pollution traps. I am no expert on these so please excuse me if I get some things wrong! I’ll give two examples of smaller traps.


The basic formula for all these traps is a "filter" which captures litter but allows water to flow through. They vary from mesh socks that are installed over the outlet of smaller storm water drains to large, engineered units with concrete foundations and steel cages built around larger storm water outlets.


Brisbane City Council Stormwater net

An Australian-designed gross litter trap

The second example above is made by Australian company Syrinx.

Here’s a photo of the type of trap installed at a storm water outlet on the creek in Bowral.


Credit: Willoughby Council

One very important point to consider with all of these traps is that they need to be emptied and cleaned on a regular basis. They can clog up quickly, initially trapping larger pieces of litter which then in turn begin to trap smaller pieces and then weeds and other debris. This could obviously block the outlet and cause water to backup and result in flooding upstream. Councils must ensure cleaning out of these traps becomes a regular maintenance task, especially after heavy rainfall!


So, do these gross litter traps work? From personal experience I know they do trap litter but how much and how efficient they are I cannot say, though I am sure there would have been studies carried out, if for no other reason than for councils to justify the costs involved in installing and maintaining them. But for now, I suggest that we, as members of BIEPA and residents of Bribie Island keep our eyes open for situations where these traps might work in our environment where they may help to reduce the amount of litter reaching the passage and our beaches. Maybe we can produce a report which we could present to council encouraging them to investigate this method of reducing pollution?




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Unknown member
Jun 07, 2022

Bribie Gardens canal residents have been asking MBRC for traps to be installed on the 36 or more stormwater outlets that drain into the canal For the last 10 year. So far no success.

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Unknown member
Jun 06, 2022

Great

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