Pond Boss Forums POND CONSTRUCTION Building a dam Dam question

Guys i made a new thread for my question since wasn't getting anywhere on the other..

My question is how high above your drain pipe do you want your emergency overflow and how high above the emergency overflow do you want the dam top???

Like Bill Cody says, "It all depends"

Do you have this booklet?

http://www.in.nrcs.usda.gov/pdf%20files/PONDS.PDF

If you read pages 22 thru 50, you will see that the answer that you are looking for depends on a lot of things that are very site specific. I'm guessing that someone with a lot of pond building experience (Mike, Tim, etc.) can give you an ballpark answer, but I can't.

I'll read it here in a little while.. Thanks I've looked online and read some stuff but nothing really with answers or even formulas..

That's way too complicated for me to figure out.. Good read though.. Do anyone know Mike or Tims email? PM me and maybe i can get a ballpark answer from them..

Otto's Dirt Service
800/882-Dirt (3478)
PO Box 2
Lindsay, TX 76250
[email protected]

I believe this is Tim:
Pinney Construction
Rr 1 Box 444, Skiatook, OK 74070
(918) 263-4016

I know this is his e-mail:
[email protected]

Hope that helps.

Thanks for the info I emailed both of them..

Bluegill

Check your PM

drp

Otto's the man.. Kept it simple 2' above the drain inlet for emergency overflow and 2' above that for top of dam..

Yes, Otto is great. He is one of the nicest people i have ever met, and he is incredibly knowledgeable.

Here's how to decide.
Figure out the size of your watershed that feeds the pond. Determine the size of pond you want to fit the site.
Remember this number...1 acre, 1 inch deep, is 27,000 gallons.
Next, learn what your average annual rainfall is and get the best guess as to what the average percentage of that rainfall is runoff. (That's based on surrounding terrain...forest, farmland, rocky soils, etc.)
Then, figure out your "100 year flood" event. From that, do the math and you'll see how much water you'll need to manage.
Remember this...your dam is a water management structure. It's designed to impound water and release excess water safely.
Many ponds have a primary spillway at pool level and then a secondary, emergency spillway above that. The primary spillway is usually a pipe, of diameter to accomodate a "normal" runoff event. The secondary spillway is designed to handle that 100 year flood event.
Here's an example of what I mean. Say there's a site for a 4 acre pond in a swale/creek that is fed by a 50 acre watershed. That part of the planet, over a 30 year average, gets 32 inches of rain/precip per year and 80% of that is runoff. That means, over a year-span, that pond will receive 25-26 inches of runoff. Over 50 acres, that's 1,200-1,300 acre inches of rain...or close to 100 acre feet. That means the pond is too small for that watershed...so the emergency spillway needs to be wide enough to dispose of excess water. In that case, freeboard (the elevation between spillway and dam) needs to be more than if that pond was 8 acres.

Here's the bottom line...most ponds are designed with 6-10" of freeboard between the primary spillway and secondary spillway. Most ponds have 3 feet of freeboard between the emergency spillway and top of dam. Those ponds/lakes with bigger watersheds have wider emergency spillways...so the water rarely flows out any deeper than 6-8".

Thanks for the info Bob.. Another question For you guys..

If you have a drainpipe sticking through a dam and say water is running through the bottom 1/3 of the pipe would a standing vertical pipe be more efficient since water will be pouring in completely around it's diameter?

Just got your email and agree with Otto keep it simple. You might be able to raise it a bit more but I would need a lot more info. Like elevations of top of dam to inlet of pipe and then outlet of pipe. Would need to know if you have a air vent welded on pipe to prevent swirl.
Keep in mind it takes a 24" riser to load a 12" pipe when water is about 3" above top of riser, a 30" riser will load it quicker. These larger risers must be anchored with concrete or something due to buoyancy. And also keep in mind that you are fixing to put more water pressure around your pipe than ever which is not a problem if you installed good anti seep collars. If you decide to bring level up to within a foot of emergency spill weld a 4" collar on bottom of riser and screw a 4" plastic cap in it. This will allow you to drain pond down and cut top of riser down some if need be.

here are some pics of a 24" pipe with vent on it and a 48" riser. The bottom of this riser has 1 ft of concrete in it when done to hold it down then another 2 yards concrete on the base to hold it down. One pic shows anti seep collars being installed we dont dig a hole anymore we put them under the pipe and push them down then weld top half on. And yes these are extremely efficient when done right.

Tim I sent you another email.. I actually made a different kind of riser than your describing.. From what Otto's told me it would not be as efficient as your setup but alot more efficient than my current setup.. I wasn't planning on anchoring this one either but now I'm thinking of welding a 3' leg on it with a 12x12 plate 3ft deep and filling with concrete to anchor it for buoyancy issues..