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