High efficiency sediment basins

High efficiency sediment basins — Key considerations

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• Overview
• Key considerations
• Planning and design
• Construction and operation
• Links and references

Requirement for effective treatment

• High Efficiency Sediment Basins (HES Basins) are fitted with an automated dispensing unit to dispense coagulant (e.g. Aluminium Chlorohydrate (ACH)) or flocculant (e.g. Polymers, chitosan) to the stormwater/irrigation water influent[1].
• The right chemical must be used at the right dosage[2].
• HES basins are located off-line from major stream/river flows and are scaled relative to the local climatic conditions and irrigation regime to treat all of the stormwater and irrigation water generated from the local connected catchment (catchments typically up to a maximum of 100ha)[1].
• The basin design promotes calm flow conditions to prevent re-suspension of settled particles.
• Accumulated sediment needs to be regularly removed from the system.
• HES basins require a 1 hour hydraulic detention time, much less than traditional sediment basins, which makes them potentially applicable to a wide range of climatic conditions and on-farm applications[1].
• Conversion of rainfall figures to run-off volumes may require expert input and/or hydrological modelling to ensure the HES basin is sized appropriately[3].

Suitability and limitations

HES basins, while not widespread in Queensland, have been used in a variety of agricultural industries to remove sediments and associated nutrients and pesticides[1]. Some trials have been conducted in Queensland[3].

HES basins have a small treatment area ‘footprint’ compared to vegetated treatment systems and more traditional forms of sediment basins.

HES basins can be retrofitted to existing irrigation tailwater recycle pits or sediment basins/traps by adding an automatic coagulant dosing units to the primary inflow point(s)[3].

New permanent HES basins can be constructed at low points (e.g. farm drainage discharge points) or small HES basins can be constructed at drainage collection point(s) from land in fallow.

HES basins do not rely on vegetation for enhanced sedimentation and are therefore less vulnerable to prolonged dry periods (such as experienced in the dry tropics region) compared to vegetated treatment systems such as constructed wetlands and bio-retention.

Monitoring and modelling of an HES basin application in several Queensland locations shows high performance for suspended sediment and nutrient retention[3].

TSS load reduction: 80-90%

TP load reduction: 70-90%

TN load reduction: 45-65%

HES basins are not a suitable treatment system in areas that regularly flood, where there is shallow groundwater or if the runoff or tailwater is saline as this increases the risk of deep drainage.

The cost-effectiveness of high efficiency sediment basins in removing the target pollutant/s needs to be considered relative to other treatment structures. Refer to cost considerations for more information.

Treatment processes

References

1. ^ a b c d Eadie, M (June 2016), 'High Efficiency Sediment Basins for Reef Catchment Applications', Treatment Systems in Coastal Catchments Forum. [online] Available at: https://wetlandinfo.des.qld.gov.au/wetlands/management/treatment-systems/for-agriculture/treatment-sys-nav-page/treatment-forum/.
2. ^ McLaughlin, RA & Zimmerman, A (2008), Best Management Practices for Chemical Treatment Systems for Construction Stormwater and Dewatering, vol. FHWA-WFL/TD-09-001, North Carolina State University, Raleigh.
3. ^ a b c d Robson, K (2015), An assessment of the performance of current best practice sediment basins vs. high efficiency sediment basins based on modelling and field studies, Stormwater Queensland, Toowoomba.

Last updated: 10 June 2022