Sediment basins

Sediment basins — Construction and operation

Select from the tabs below

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

Approvals

Approvals may be required for the construction of a sediment basin. Contact your local government before any construction is undertaken to understand requirements.

For example:

• Sediment basins should be sited to avoid damage to vegetation, but if it is unavoidable and vegetation removal is required, approvals may be required.
• High impact earthworks within the vicinity of an area mapped as a wetland protection area may trigger an approval process.
• As sediment basins can capture stormwater run-off, approvals may be required for taking overland flow.
• Prior to construction, check for any existing infrastructure by contacting electricity, water and telecommunication providers.

It is also recommended that local Traditional Owners are engaged to ensure no sites or items of cultural significance are disturbed during excavation.

Engineering advice should be sought prior to construction to ensure the sediment basin is sized and sited appropriately, taking into account soil suitability, groundwater and local hydrology. The stability and safety of the sediment basin should also be considered.

Construction

Construction of a sediment basin involves a number of steps, including:

• Earthworks to create the excavated settling pond/storage area and the access pad.
• Construction of an inlet and outlet (and possibly high flow bypass).
• Stabilisation of the soil around the basin.
• Possible planting.

A vegetated sediment basin will require consideration of levels needed for plants to establish and thrive. If the sediment basin is to be vegetated, topsoil should be stripped, stockpiled, and respread in the basin.

Case study: Installing a sediment basin on a cane farm in the Burdekin.

Establishment

A sediment basin can start trapping sediment as soon as it is built.

The batters of a sediment basin should be stabilised with grasses or groundcovers to prevent erosion.

A vegetated sediment basin will require plants (mainly reeds and sedges) to be established throughout the sediment basin. Refer to establishment of treatment wetlands for more information.

Operation

Sediment basins do not require active operating other than maintenance as described below.

Monitoring and maintenance

Sediment basins should be inspected for damage and to assess sediment accumulation every six months, or after every major rain event.

Typical maintenance of sediment basins will involve:

• Removing sediment when capacity is less than half the storage volume and before the start of the wet season. A marker post could be installed within the sediment basin to indicate when half the storage area has been filled. The sediment basin should be designed to have sufficient storage so that desilting is required infrequently (e.g. once every five years[1]). Machinery and access will be required. Removed sediment should be placed in a location where it can dewater away from drainage lines and natural waterways (ideally upstream of the sediment basin so flows can drain back into it). Once sediments are dried, they should be removed and can be used back on the paddocks.
• Repairing any erosion on the batters.
• Removing blockages and repairing erosion or damage of inlets, outlets and bypass structures.
• Removing weeds before they spread and/or set seed.
• For vegetated sediment basins, it is important to maintain healthy vegetation to ensure the sediment basins are not colonised by weeds. The most intensive period of maintenance is during the plant establishment period in the first two years when weed removal and replanting may be required.

Lifespan/replacement

With regular maintenance to remove accumulated sediment, sediment basins should last indefinitely.

References

1. ^ Department of Employment, EDI (2011), Wetland Management Handbook: Farm Management Systems (FMS) guidelines for managing wetlands in intensive agriculture.. [online], Queensland Wetlands Program, Brisbane. Available at: https://wetlandinfo.des.qld.gov.au/resources/static/pdf/resources/reports/fms/fms_025_handbook_web.pdf.

Last updated: 5 November 2022