Decommissioning a Dam: Removal and Site Rehabilitation

An unwanted dam should not become an unplanned earthmoving job. Before booking machinery, decide what you want the finished site to do: retain a smaller storage, support a different use, or stop functioning as a dam. Put that objective alongside the water supplies, access routes and neighbouring land that the project must protect.

As of October 2026, the NSW and Victorian guidance discussed below provides useful starting points for planning, but not a single approval pathway for every Australian farm. Treat this as a guide to commissioning the assessment and defining the work. It is not a set of instructions for opening a dam wall or releasing stored water.

What does decommissioning a dam involve?

For project planning, distinguish removal from repurposing. Dam removal means taking away some or all of the structure; repurposing means changing the use of the retained asset. Write down the proposed end condition rather than assuming that everyone quoting the job has the same meaning of decommissioning.

Victoria’s decommissioning and repurposing guide uses four decision-making stages to compare future management options before implementation, including retaining the dam rather than automatically proceeding to removal (Victorian guide for dam owners).

Option to assess	Question for the project brief
Retain and repair	Can the dam meet the property’s needs with an acceptable repair and maintenance commitment?
Repurpose or partly remove	What water, structure and management responsibilities would remain?
Remove the storage function	How will runoff pass through the finished site without recreating an unwanted impoundment?

Compare those options against the same brief, including replacement stock water, possible firefighting use, environmental values and future maintenance. Do not compare a repair price with a removal price that excludes sediment handling and rehabilitation. Our dam repair and rebuild guide can help frame the retain-and-repair alternative without deciding the outcome in advance.

Make the proposed final land use explicit. A grazed paddock, a rehabilitated drainage corridor and a retained wetland need different assessments. Ask the designer to show what remains on the plan, who will manage it and how the site will perform when water returns after rain.

Which approval checks come before dam removal?

Prepare a property plan, existing licence and approval details, photographs, the reason for removal and a description of the intended finished site. Ask the relevant water authority and council which permissions apply, then check whether dam-safety, waterway, vegetation, heritage or ecological matters need separate assessment. Do not assume an old construction approval also authorises removal.

For NSW declared dams, Dams Safety NSW requires owners to notify it before decommissioning and continue normal inspections until the dam is omitted from the declared-dam Gazette list, which is normally published twice yearly (NSW decommissioning and declaration guidance).

A declared dam is one formally included in NSW’s dam-safety regulatory system. Check the actual status of your dam rather than applying the declared-dam process to every farm storage. If declaration applies, ask what evidence is needed for its removal and keep the regulatory close-out separate from the contractor’s completion of earthworks.

Victoria’s published works-licence policies require a licence condition for removing or decommissioning a potentially hazardous dam that engages a suitably qualified engineer to supervise the work and prepare a completion report within 30 days of completion (Victorian works-licence policies).

That deadline concerns a specified Victorian licensing situation, not the duration of a removal project or a national rule. Ask the licensing authority to confirm your dam’s classification, the required plan and the conditions that will govern the work. Elsewhere, obtain the equivalent property-specific advice from the relevant state authority before committing to a start date.

How should drawdown and sediment management be planned?

Drawdown is the lowering of the stored water level. Have an appropriately qualified dam engineer specify the method, sequence, monitoring and stopping conditions for your site. Do not cut through a water-retaining wall to find out how it drains, and do not choose a pumping rate from a generic online example.

Ask the assessment to address the stability of the existing wall during lowering, the receiving area’s capacity, water quality and the route of any discharge. Include a plan for rain arriving during the work. Identify who can authorise a change in the sequence and what site observations require the contractor to stop and seek advice.

Sediment management is the planned handling, retention or stabilisation of material accumulated in the storage. Commission an assessment of its amount and condition before choosing how to expose or move it. Ask whether sampling is needed, where material can lawfully go and how disturbed areas will be kept from washing into downstream drainage.

Do not assume every deposit needs excavation, or that every deposit can remain undisturbed. Have the environmental and engineering advisers compare the options for this site. Include access to the material, temporary storage, treatment where required, transport and final placement in the scope so that the excavation price does not hide the disposal problem.

Keep this distinction separate from routine cleaning out a silted-up farm dam. Desilting seeks to recover storage capacity; a removal project needs a plan for the landscape after that storage function has changed. Do not use a cleanout specification as a substitute for a decommissioning design.

What belongs in the site rehabilitation design?

Site rehabilitation is the work needed to establish the agreed stable landform and vegetation after disturbance. Ask for drawings that show final ground levels, the water’s future route and any structure to remain. Include the connections to undisturbed ground upstream and downstream, not only the opening through the old wall.

Have the engineer assess whether retained wall sections, outlets or foundations need treatment. Request a design for erosion protection and ask how flood flows and temporary blockage have been considered. Avoid selecting an opening width, slope or rock size from a photograph of another dam: ask for the calculations and site assumptions supporting the proposed detail.

Plan vegetation establishment alongside earthworks, including suitable local species, topsoil handling, weed control and protection from stock. Specify what needs to be in place before the contractor leaves. Where vegetation needs time to establish, identify the temporary protection and who will inspect and repair it after rain.

Include redundant pipes, pumps, cables, fencing and access tracks in the inspection. Have services located before excavation and agree what will be removed, isolated or retained. Keep people and stock away from incomplete works, and make access restrictions part of the site plan rather than an informal instruction remembered by one operator.

How do you define the scope and prove completion?

Build the estimate from the assessed method, not a flat allowance for excavator days. Request separate allowances for investigations, approvals, temporary water management, sediment work, earthworks and rehabilitation. Identify uncertain quantities and hold points before accepting the scope. A hold point is a nominated stage where work pauses until a specified inspection or approval is complete.

Lindsey Hughson’s retained close-out correspondence for a completed Big Ditch dam project at Lorne, NSW in 2019 records 76.5 excavator hours. It is evidence of a completed construction job, not a decommissioning case study or a benchmark for removing another dam.

Use that distinction when reviewing your own records: machine hours describe effort, while the approved design and completion evidence describe the required result. Ask for a handover package that matches the project conditions, including photographs, survey information where specified, inspection records and any engineer’s report. Record departures from the plan and how they were resolved.

1. Define the finished site’s purpose and replacement water needs.
2. Compare retaining, repurposing and removing the dam.
3. Confirm approvals and commission the necessary engineering and environmental assessments.
4. Agree the work sequence, inspections, hold points and weather contingencies.
5. Document completion against the approved scope and regulatory conditions.
6. Assign post-work monitoring, maintenance and corrective actions to a named person.

For the handover, specify inspection triggers, access arrangements and the process for reporting erosion, settlement or unwanted ponding. Adapt the inspection discipline in our farm dam maintenance checklist to the agreed post-removal plan rather than assuming the old checklist remains sufficient. Keep responsibility clear if the property or retained asset changes hands.

If the project is still at the options stage, ask Big Ditch to assess the existing dam and proposed site work. Bring the authority’s advice, existing plans and your intended end use. We can discuss the practical earthworks scope without treating a contractor’s inspection as a substitute for engineering design or regulatory permission.

Frequently asked questions

Can I cut a gap in the wall and let the water out?

No. Do not make an uncontrolled opening in a wall retaining water. Obtain a site-specific assessment and an agreed drawdown and works plan before disturbing it, including downstream and sediment controls. If the dam appears to be failing, keep people away and seek urgent professional or emergency assistance rather than starting an improvised removal job. A planned decommissioning project is not an emergency breach response.

Does removing a dam end all maintenance?

Do not assume maintenance ends when the machinery leaves. Define the post-work inspection and maintenance duties in the design and handover, including responsibility for vegetation, drainage and any retained structures. Ask the relevant authority what evidence is needed to close the regulatory process. Keep those documents with the property records, and arrange follow-up work if the finished site does not meet the agreed objectives.

Can an old dam become a wetland instead?

Consider a wetland as an option to assess, not an automatic outcome of leaving water behind. Ask an appropriately qualified environmental specialist and engineer to examine the proposed water regime, habitat, retained structure and maintenance requirements. Include any necessary approvals and replacement water supply in the comparison with repair or removal. Agree who will manage the wetland and how its performance will be checked.

Considering decommissioning a dam rather than repairing it? Book a site inspection with Big Ditch and define the site work before disturbing the wall.