Flashboard riser installation

[Duck Engr]

Looking for some do's and don't's of flashboard riser installation.

A little background:
This is a low field alongside a ditch that holds water annually. We've built a levee around the field, now it's time to install the pipe and riser. I've run the runoff calcs, time of concentration, the whole 9 yards. Ended up with a 36" pipe (this area drains a large hillside). Bought a steel painted riser from osceola machine for a plastic corrugated pipe. The soil where the impoundment is located is red clay, sometimes gray clay, so no issues with holding water. A problem with that dirt is it eats through metal quickly.

Most flashboard riser installs i've seen bury half of the riser into the levee. I'm worried that'll greatly reduce the life of my riser due to corrosion. I'm wanting to pull it out into the impoundment a few feet and have it stand alone. Now my next issue, that pesky buoyancy thing. Water will be 4' deep at full pool. Riser is 2' deep x 3.5' wide. that weight of water comes out to 1,750 lbs. Riser only weighs 185. Ideally, i'd pour a big chunk of concrete and anchor it to the concrete, but i doubt we can get a concrete truck back to that area. I've also considered anchoring it into the soil using auger-style anchors.

My most recent idea is to put the riser on the back end of the pipe, outside of the levee. It'd basically be turning the system around backwards. Water flows in the pipe first, then through the riser and over the boards. No buoyancy problems then but water will be trying to push the riser off the pipe and once a stick gets in there, it won't be able to escape (unless there' s a big rainfall event) until i pull a board or two. Beavers are around, so i'll install a hog wire fence guard around the inlet. Also planning on putting in a seep collar.

Anyone ever seen a flashboard riser installed outside of the levee?

[novacaine]

The only issue i see is the non water tight connection from the flashboard to pipe. You set up is probably using screws thru pipe and into the flashboard starter. It may leak around that.

I have cantilivered the flashboard on the inlet side (after making watertight with spray insulation, calk, etc) and drove 2 channels (1 on each side of the flashboard vertical channel guides) into the ground (support and bouancy) and drilled thru guides/channel sections.
You still need to be able to get to the front of the flashboard structure to put in boards and take them out.

[Duck Engr]

Thanks for the response Novacaine. You’re correct, planning to use self-tapping bolts to connect the pipe to riser. Also planning to use “great stuff” spray insulation to seal along with silicone if need be on any cracks. I like your idea about the channels and directly anchoring the riser to those. That would avoid cables stretching and allowing movement up which might compromise my levee. Thanks for the input.

[novacaine]

I cant find my old picture of an install. Sorry