Your Dam Your Responsibility (PDF~1.2MB)

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9 Decommissioning of Dams
9.1 Removal or Decommissioning of a Dam
Where a dam may have outlived its usefulness or economic life and if you wish to remove
or decommission it, you need to obtain a licence.
An owner cannot simply walk away from a farm dam because it is of no further use
or is too costly to manage or rehabilitate. Instead, the dam must be either removed or
decommissioned. In either case, it should be made incapable of storing any water either
temporarily or permanently. Decommissioning other than by removal is normally done by
breaching one or more sections of the dam wall or embankment.
The dam owner is still responsible for ensuring the safety of residents and development
downstream, and of the dam itself while it is in the process of being removed or
decommissioned, and indefinitely afterwards if it is not removed but decommissioned.
Removal or decommissioning of a dam is not without its problems, and thought should
be given to the following:
• Has an assessment been made of the costs associated with the removal?
• Will the proposed works eliminate any future operation, maintenance, surveillance or
remedial work?
• Can the unbreached sections, if any, be left in a permanently stable condition?
• Is the proposed breach wide enough not to impound significant quantities of water
under flood conditions?
• Has the short and long-term stability of any sediment deposits within the reservoir
area been considered before commencement of the breaching operation?
• Is the breaching process acceptable from safety and damage perspective both at the
dam and downstream?
Breaching should not be attempted while there is any water in storage unless expert
advice is first obtained.
Environmental aspects downstream must also be considered before a dam is breached.
Siltation/sediment transport or erosion caused as a result of decommissioning could
become a liability on the dam owner.
It should be noted that the cost of rendering a dam that is of no further use safe
(particularly against storm and flood events) could be considerable. For any dam being
decommissioned or breached, professional engineering and environmental advice should
be obtained.
9.2 Rehabilitation of Site (After decommissioning)
For all dams, a plan for rehabilitation will need to be presented to the Licensing Authority
for approval. The plan is required to explain how the land or waterway will be managed
to minimise erosion or degradation impacts.
A dam breach that results in some portion of the dam wall being left in place, is not
necessarily sufficient action. This is because any flow obstruction effect during floods will
be an obstacle compared to the natural waterway characteristics.
It would be difficult to defend due diligence where a flood event erodes the remaining
dam structure and results in a sudden release of water or mud flows that causes loss of
life or damage to property or the environment.