Last updated: April 2026 | Author: Angus Hughson, Big Ditch Dam Building Company
A storm cell about to drop its load into Dam No. 5 at Big Ditch HQ. 6.10 pm 17 March 2020 causing a huge dam overtopping.
The dam is at 102% capacity, and due to wall shrinkage during 18 months of drought, the spillway became unbalanced by 1% in relation to the freeboard, causing some excess volume to start gently rolling over the dam wall.
We always construct dam walls with gentle rollover characteristics – so in the unlikely event that there is overflow, the flow doesn’t dig into the wall as it travels over the apex
Handling the Dam overtopping issue
Our young apprentice Kaleb heroically spent his day in a little 1.8 ton excavator in the pouring rain taking out 600mm of spillway floor to re-balance the freeboard from -200mm to +400mm.
The danger was that if we receive the heavy falls predicted this weekend, the outflow over the wall would become destructive and start chewing into the wall and possibly cause a wall collapse. But Kaleb increased the spillway flow, and increased the freeboard enough to deal with any further torrential downfalls – and he gave us a margin for safety, while also maintaining the infinity dam effect achieved with minimal freeboard design
Frequently Asked Questions
How much does it cost to managing overtopping: controlled overflow techniques for earth dams?
Costs vary significantly depending on dam size, soil conditions, location, and access. Big Ditch provides fixed-price quotes after a site inspection. Contact our team for an accurate estimate tailored to your property.
Do I need council approval for managing overtopping: controlled overflow techniques for earth dams?
Requirements vary by state and dam size. In NSW, QLD, and VIC, dams above certain storage volumes require approval. Big Ditch handles all regulatory compliance as part of our service — contact us to discuss your specific situation.
How long does managing overtopping: controlled overflow techniques for earth dams take?
Timeline depends on dam size, soil type, weather, and site access. Most farm dam projects take between 3–14 days of machine time. Big Ditch will give you a realistic schedule during your site inspection.
Can Big Ditch help with managing overtopping: controlled overflow techniques for earth dams?
Yes — Big Ditch specialises in earth dam construction, repair, and maintenance across Queensland, NSW, and Victoria. We offer fixed-price quotes, 10-year guarantees, and over 30 years of experience. Call us or book a site inspection to get started.