Sediment extraction

In-channel sediment extraction for rehabilitation is commonly undertaken as an action to address bed build-up (aggradation) associated with excess sediment deposition from reaches up or downstream. Historically in-channel sediment extraction (e.g. for sand) has occurred commercially often resulting in the degradation of the channel both at the site, upstream and downstream. It has limited application and requires specialist technical input to ensure any potential adverse impacts are considered and mitigated as well as meeting legal requirements.

Sediment extraction works to rehabilitate the river may occur over the entire width of the riverbed, or on discrete deposition features (e.g. point bars). Sediment extraction works are also undertaken:

• to address bed build-up (aggradation) associated with an instream barrier which acts as a sediment trap, preventing sediment from transporting into downstream reaches.
• to increase channel capacity, where there is a flow capacity/flood impact.
• to provide more favourable aquatic habitat conditions.

Potential benefits from this intervention:

• Allows for rapid removal of excess in-channel sediment, potentially improving sediment transport capacity, channel capacity, channel depth and diversity.
• May prevent excess sediment inputs from entering up or downstream reaches.

Potential negative implications from this intervention:

• Sediment extraction has the potential to initiate channel instabilities (both bed and bank erosion) which can result in substantial changes in both an upstream and downstream direction.
• Sediment extraction can increase sediment transport capacity through the extracted reach, increasing the efficiency of sediment transfer into downstream reaches.
• Sediment extraction has the potential to cause significant site/reach disturbance due to heavy machinery access requirements.
• It is often difficult to find suitable sediment stockpile locations.

Intervention considerations:

• Seek appropriate specialist advice and check legal obligations (e.g. permits).
• Determine the cause of sediment aggradation. Excess sediment deposition received from upstream reaches will be more effectively managed by addressing the source of the problem (e.g. erosion management or barrier removal).
• The disturbance and cost associated with sediment extraction may not justify physical intervention.
• Safety of employees including seasonal exposures (e.g. heat) and high risk areas (e.g. crocodile presence in waterways or areas with soil contaminant risks).

Additional information

Publications:

Rutherfurd, I.D., Jerie, K. and Marsh, N. 2000. A Rehabilitation Manual for Australian Streams, Volumes 1 and 2. CRC for Catchment Hydrology and LWRRDC. Canberra.

Sims, A.J. and Rutherfurd, I.D. 2017. Management responses to pulses of bedload sediment in rivers. Geomorphology 294, pp.70-86.

Last updated: 10 June 2022