High efficiency sediment basins

High efficiency sediment basins — Construction and operation

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

Approvals

A range of legislation and approvals may be required for the construction of a HES basin. Contact your local government before any construction is undertaken to understand requirements.

Prior to construction, check for any existing infrastructure by contacting electricity, water and telecommunication providers.

Engineering advice should be sought prior to construction to ensure the basin is sized and sited appropriately, taking into account soil suitability, groundwater and local hydrology.

Construction

HES basins will require earthworks to excavate a pit.

The angle of the batters will depend on the soil type, but generally, batters should be less than 2.5:1 and no steeper than 3:1 unless reinforced by stabilising material. The upper batters should be stabilised with jute matting or non-invasive grass to prevent erosion. An inlet and outlet into a farm drain also need to be constructed and can be either an open drain or pipe.

Spoil should be returned to the farm, or disposed of away from natural wetlands and waterways (Subject to ensuring that the aluminium content of the material and other factors are acceptable for agricultural use). The spoil disposal site should be bunded to avoid sediment loss.

Establishment

An HES basin can be constructed and operational within a month of construction (will depend on the size of the structure).

Operation

Operation of an HES basin requires:

• Dosing appropriate volume of coagulant. Applied at correct dosing rates and within optimal raw water pH range, if correctly dosed ACH will produce residual aluminum levels below drinking water and aquatic ecosystem guideline limits.
• Dosing should be adjusted according to water inflow measured using flow or level sensors.
• Removing and desilting collected sediment periodically from the first part of the HES system.

Maintenance

Typical maintenance will involve:

• Inspecting and maintaining coagulant supplies.
• Inspecting dispensing system for correct operation (rain/flow sensors; telemetry (if installed)), and rectification when required.
• Inspect structural and hydraulic integrity of basin and basin outlet and rectification when required.

Monitoring

Basins should be inspected regularly and after every major rain event to ensure the structure and pumping infrastructure has not been compromised.

Lifespan/replacement time

10 year replacement of coagulant dispensers.

20 year re-set of basin to original design.

Last updated: 10 June 2022