It is well known that established urban catchments often result in increased flow to receiving streams, but they can also lead to reduction in coarse-grained sediment to receiving streams. The resulting loss of coarse-grained sediments (e.g. sands, gravels etc.) in streams has negative consequences for aquatic ecosystems, including reduced foraging and refuge for macroinvertebrates and fish. Stormwater harvesting and treatment systems often exacerbate the problem. Gross Pollutant Traps (GPTs) are commonly designed to remove particles and particulate-associated contaminants from reaching the water body, further starving streams of coarse-grained sediments. Passing coarse-grained sediments through these systems, however, risks transporting associated pollutants to the receiving water body. This paper reviews the literature on particle size distribution, pollutant concentration and the effect of particle size on pollutant concentration before and after GPTs. We also outline initial findings from a field sampling study on a GPT on the outskirts of Melbourne, Victoria. The results suggest that stormwater treatment systems may be more effectively designed for specific sediments sizes, with the high pollutant particles captured and low pollutant particles redirected to the stream. This will help us consider alternative designs to simultaneously mitigate pollution, maintain stream health and reduce the cost of maintenance.


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