Litter and sedimentation management systems are basic treatment methods that keep gross pollutants in place. Litter and debris are the most popular forms of gross pollutants and coarser sediments.
Litter includes human-made garbage such as paper, polyester, styrofoam, metals, and glass. Coarse particles are often inorganic degradation products of soils, pavements, or construction materials. Gross pollutants are waste items bigger than five millimeters, and coarse sediments are grain sizes more than 0.5 millimeters in diameter. Some contaminants endanger animals, impair aquatic ecosystems, diminish aesthetic characteristics, leach dangerous substances, and attract vermin.
However, non-structural management strategies such as trash collection, container design and positioning, sedimentation controls, sidewalk sweeping, and limiting usage of deciduous plants get the ability to minimise litter and particle inputs to the drainage system.
What utilised sediment and trash management systems in Australia?
In Australia, sediment and garbage management solutions range from purification for the higher reaches of the watershed to slow-moving streams deeper down the catchment. Such systems are suited for fitting to an already pipeline drainage system, especially in densely populated regions, and deliberately targeting issue areas with large loads of gross pollutants.
- Gross pollutant traps GPTs are sedimentation traps with a weir and garbage rack on the discharge side. Flows enter a large, often concrete-lined basin and are held in place by a weir, reducing flow velocity and fostering sedimentation.
The garbage rack gathers rubbish from flows that overflow the weir. GPTs serving small catchments can locate underground. These devices frequently involve a series of underground chambers, spillways, screens, or obstacles to control flow and trap sediments.
- In addition, the continuous deflective separation device is an alternate below-ground system that works by channelling rainwater and pollution into the chamber with a circumferential screen that creates a vortex to maintain pollutants in constant movement, preventing sediments from ‘stopping’ the screen. The vortex-induced secondary flows focus on silt at the unit’s bottom. Water flows down after passing past the screen.
Additional types of trash and sediment traps include:
- Grate and side entry screens are metal screens that protect the drainage channel’s intake and prevent heavy trash objects from entering and obstructing the drain.
- Baffled pits are stormwater pits in a series of baffles built to capture floating trash and help sediments to sink.
- Circular settling vessels arise from a concrete slab tank beneath the ground, separated between an above-diversion section and a lower retention chamber. The diversion spillway at the entrance sends runoff into the lower retention tank, where silt sinks to the chamber’s bottom.
Efficiency of performance
Manufacturers have built unique products to capture and filter trash and silt from drainage systems, and these technologies were not properly field tested. However, monitoring a GPT absorbing runoff from the 50 ha catchment to the unit retained almost all gross pollutants while having little influence on flows. As a downstream control, the CDS device utilised the conjunction with side entry pit trapping installed at all roadway drain entries.