Leaking Dam Triage: Will Bentonite Fix Your Dam?
60-second dam check
Answer four questions about your dam. The tool tells you whether a drained bentonite treatment is worth planning, whether the site needs assessment first, or whether the dam wall should be checked before any material is ordered. It is a screening guide, not a site assessment.
How the triage check works
Sodium bentonite reduces seepage through a dam floor and walls when it is applied to a suitable, prepared and compacted surface. It does not repair a failing embankment, a leaking outlet pipe or a spillway problem. The check above sorts a dam into one of three outcomes so you know what to do next before you spend money on material.
- Check the wall first. Any sign of piping or embankment instability sends you to a structural assessment. These signs include muddy seepage below the wall, a boggy outer batter, crest cracking or a sinkhole.
- Assess the site first. A dam that cannot be emptied, coarse or fractured ground, and dispersive or unknown soil all need a closer look before a treatment method is chosen.
- Plan a drained treatment. A stable dam on suitable soil that can be emptied is a candidate for a mixed or pure blanket at Bentonite Pro’s recommended 30 kg/m².
Why the dam wall comes first
The NSW DPI guide to leaking farm dams identifies leakage through unsuitable embankment material, beneath the wall, and through exposed rock, sand or gravel in the basin. Water that carries soil out of the wall is eroding it from the inside. Treating the basin surface does not address that, and working machinery on a weakened wall can be dangerous. If you see these signs, keep people and stock away and have the wall inspected.
Why the dam needs to be emptied
Both standard methods need a dry, cleared surface. For a mixed blanket on light or loam soils, bentonite is worked into the upper 150 to 200 mm of soil and roller compacted. For a pure blanket on heavier soils, bentonite is spread, covered with at least 100 mm of site soil, or at least 450 mm where stock have access, and then compacted. NSW DPI describes broadcasting bentonite over open water as “at best hit and miss” and does not recommend it because success cannot be assured. The full method is set out in how sodium bentonite seals a leaking dam.
Why soil type changes the answer
Bentonite works with the soil it is mixed into or covered by. Light and loam soils suit a mixed blanket. Heavier soils with some clay suit a pure blanket under cover soil. Clean gravel, sand seams and fractured rock may need more cover, a different treatment or a liner. Dispersive clays, which cloud water when wet, behave differently again and should be tested. The bentonite soil suitability guide explains each case.
Working out how much bentonite you need
Bentonite Pro’s recommended rate is 30 kg/m² across the total treated area, floor plus walls. One 1.2 tonne bulk bag holds 1,200 kg, so it provides material for 40 m² before any site allowance. Bags are supplied whole, so the bag count is rounded up. Use the bentonite calculator for tonnes, bags and cost, and the freight calculator for delivery to your address.
Common questions
Can I fix a leaking dam without emptying it?
Do not rely on it. NSW DPI does not recommend broadcasting bentonite over water because success cannot be assured. If the dam cannot be emptied, arrange a site assessment.
Is a falling water level proof of a leak?
No. Evaporation, stock use, pumping and outlet losses all lower a dam. Rule those out first. The guide to telling leakage from evaporation sets out the checks.
What does muddy water below the dam wall mean?
It can mean water is carrying soil through the embankment, a sign of piping. Treat it as a structural issue. Keep stock and vehicles off the area and have the wall inspected before any repair or material order.
How many bulk bags does a 1,000 m² dam need?
At 30 kg/m², 1,000 m² needs 30 tonnes, which is 25 bulk bags of 1.2 tonnes, before any site allowance.