How to shore up a wooden pond spillway?

[plowhog]

My pond spillway is concrete. It has a provision to put boards across the face of it, horizontally, to prevent water from escaping and raise the pond level. The boards currently are 2 x 8's. About 40" from side to side, and I can stack 3 more boards on top of the first.

The 2 x 8's act as a dam when the pond level rises, but it leaks everywhere. From under the "bottom" 2 x 8 where it touches the concrete, along the sides where the 2 x 8 edges touch the concrete, and in-between each 2 x 8 stacked on each other.

A few questions:

1. What would be a good sealing material between the wood barrier and the concrete?
2. A single sheet of plywood could replace several of the bottom boards. Do you think 1 1/8 plywood is strong enough?
3. If I use plywood, how should I paint or treat it before it goes into service?

 

[CobyRupert]

Does the bottom board sit flush on the concrete? Maybe bottom edge of bottom board needs to be “scribed” and cut to match the exact contour of the concrete?

 

[plowhog]

Does the bottom board sit flush on the concrete? Maybe bottom edge of bottom board needs to be “scribed” and cut to match the exact contour of the concrete?

The concrete on bottom is flat. No special notch or edge. Just a flat board sitting on rough concrete-- leading to leaks.

On the sides, there is an extra "lip" or "edge" on the concrete on the side opposite from the water. So the boards can push up against that lip when holding back water. Again, it sort of seals, but leaks.

 

[Topzide]

What about using packing just as you would on a wooden boat? Same principle and maybe a lap joint as they stack will help out also. Other than that, maybe some sort of rubber gasket like a door seal on a truck. Good luck.

 

[MossRoad]

Can you put a seal on the bottoms of each board before you slip them into place? Likewise, can you put a seal on the downstream face of each board where it contacts the channels on each side?

 

[Thomas]

Maybe thick rubber or horse mat might help.

 

[frogracer]

Wood Boards are going to warp in short time. I have a dam spillway that is purpose built and uses aluminum C shaped “2x4’s”. We lay a bead of grease from a typical grease gun along the edges and smooth face ends. These then are pressed against each other by hand and all water is sealed.

Using these type boards along with a gasket type material on the bottom interface may work for you. Look up SIKA water stop products.

Not the greatest pics but may give you an idea.

Pond full and pond empty.

 

[plowhog]

Look up SIKA water stop products.

Those look interesting, but I'm not sure which of their many products would work. I'll try to get some photos of the spillway which may help ....

 

[frogracer]

One way to do this if you can locate the smooth aluminum boards - like in my photos - is the install smooth silicone aluminum place 1/16” or 1/8” thick along the flat face and then up the down stream face of the vertical groove which the boards slip into. This would then allow you to use typical heavy duty grease like I do to make a water tight seal.

When I want to break the seal / lower the water I take a putty knife at the seam and just tap it in and it very easily takes a board off.

You could use liquid nails to glue these aluminum plates in.

The hydraulic water pressure keeps the dam boards pressed against the back or down stream vertical edges for no leaks.

 

[frogracer]

Here are a couple of pics from the other side of the dam overflow.

Ignore the boards. The 2x4 floated in and the ply wood is what I call the coyote perch - find their crap on it all the time (it’s been there for years - I need to remove it.).