Why do dam repairs often fail?

Farmers may be considering repairs to leaking or failed dams to increase their water storage capacity.
Dam repairs, however, are often high-risk and expensive and should only be undertaken when the cause of failure and repair options are well understood.
Repairs should only be attempted on larger, well-constructed dams. Understanding the dam's history – who built it, what equipment was used, and how it has performed – is essential before any work begins.
Poor construction, unsuitable materials, inadequate compaction and soil contamination are among the most common causes of dam failure.
While poor maintenance can contribute, it is rarely the primary factor.
Diagnosing the cause of dam failure can be complex. It is important to determine whether the leak is through the wall or floor of the dam, and whether it is isolated or widespread.
Thorough inspections should ideally be carried out across multiple seasons, including winter, spring and summer.
Where possible, landholders should:
Inspect the dam bank for seepage, subsidence, cracks, or tunnels;
Check the waterline for whirlpools or surface turbulence;
Examine downstream areas for soft ground or lush vegetation, indicating seepage;
Use a steel probe or crowbar to test soil firmness in suspect areas;
Watch for unusual signs such as bright yellow or very clear water, which may indicate tunnelling or unsuitable soil;
Monitor and photograph the site regularly to track changes in water levels or visible issues;
Inspect the dam after heavy rain to identify potential problems; and,
Carefully examine any breach in the dam wall, looking for signs of unsuitable materials like sand, gravel or topsoil.
Soil testing is a crucial part of any repair effort. Testing should include samples from the failure site and surrounding areas, as well as any potential borrow pits.
Basic soil assessments, including texture, aggregate stability and shrinkage, can be undertaken by landholders using simple guidelines available on the Agriculture Victoria website: Soil materials for farm dam construction.
Repair options depend on the location, cause and severity of the failure.