Pond Boss Forums POND CONSTRUCTION Building a dam 12" valve or water control structure

Not sure if this is the correct area to be posting this but I'm looking to install a 12" plastic culvert as my main pond overflow and I would like the ability to block it off in order to flood a portion of my lake during duck hunting season. I have used Agridrain and another company that was slightly cheaper than agridrain on other wetland projects, however in this case I don't need to be able to adjust the water level as it will only be backed up a little over a ft before it hits the secondary overflow. Hoping to save some money and not spend $1,500 on one of those water control structures since I really just need an open or shut type valve. I'm only tossing out the 12" plastic culverts because they were the cheapest on the last project that we did. Frankly I'm finding a ton of "left over" stuff posted on craigslist and Facebook market place so if there's a valve that that will work on a different type of pipe there's a good chance that I can find that pipe for a decent price now. I do want to keep it to a minimum of 12" diameter though. Thanks in advance.

Have you ever heard of a "turn down elbow"?

Basically, you run the outlet pipe just barely tipped past horizontal through your dam structure. Then you install an elbow with an extra extension of straight pipe at the downstream end of your outlet pipe. The height of the pipe extension can then be used to control the water level in the pond. Want the pond level 5' above the outlet pipe elevation? Then stand the 5' extension straight up. Only want 3' of water, then turn down the elbow a little so the pipe extension is at an angle.

You must block the elbow so it cannot separate. I believe that is sometimes called a "thrust block". Full flow through a 12" culvert will be impressive, so you will need some kind of splash pad that covers flow from every extension pipe position.

This type of outlet becomes less structurally stable as the diameter increases and would probably require some heavy bracing to survive a flood event.

You could make a very secure outlet at the discharge end and put the turn down elbow on the upstream side of your outlet pipe. You could put the elbow at the end of dock or just wade to change the position. However, the water is pretty chilly during duck season!

Another option would be to build your 12" outlet in the simplest fashion and design it only for flood control. You could then build a moveable siphon out of 6" PVC or even flexible pipe. A 6" siphon would draw the pond down pretty quickly after duck season to your desired "spring pool elevation". You could then remove the siphon and your lake level would go back up during the next rain, whereupon you might have to drain as needed. Or you could create a permanent siphon installation that would break the siphon flow at the desired level.

Here is a link to a good automatic siphon drawing.

Siphon Schematic - (from Pond Dam Piping)

I have heard of a turn down elbow, and that's a great idea.

Mostly wanted to go with 12" just because that will be the main drain, and in the past we have had smaller diameter tubes get clogged with floating debris, however this location may be a little better suited to not have to deal with debris.