Pond Boss Forums POND CONSTRUCTION Building a dam repairing spillway wooden gates

You might be able to find a piece of 60mm pond liner or roofing membrane. Cut that to fit and replace the previous hardboard like material?

Flashboard riser systems like that always leak a bit of water between the boards as there is no "seal" between the boards. Maybe that hardboard like material was put there to minimize the leakage between the boards?

The closer the boards fit together, the less water will leak.

I wonder if the SoilFloc Polymer treatment that TJ sells would help seal those type of leaks??

I almost forgot, yes, I would replace all the boards at once.