Pond Boss Forums INTRO Questions & Observations Size for overflow and siphon system.

We have a 4.5 acre pond that was built in the late seventies with DER approval and help. A few years after it was built a hunting cabin was built on the next property (in the flood plane even before the pond was built). Somewhere in the same time frame Pa. established thier dam commision. About 5 years ago Pa. decided that because of the cabin and the acre foot of water held back by our dam during the 100 yr. flood prediction we were a C2 (dangerous regulated dam). After some exspensive work we have found out that we can be droped to a C4 (does not require exspensive annual inspections, permits, EAP or many otehr exspensive and time consuming actions). In order to get around draining the pond for an inspection and altering of the original emergency drain I am planning on adding a siphion/overflow system. Prior to the proposed changes the maximum water retained was calculated to be at 68 acre foot, after the changes we will be at app. 40 acre foot or even less depending on how far down we go with the water level and emergency spillway. My question is can I get away with 8" pipe wich is much more affordable than 12"?

Hard to answer that question without a lot more detail like drainage area etc. See this NRCS publication that give pipe sizing calculations.
http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_030362.pdf

Bingo. The drainage pipe has to be sized according to the area that drains into the pond, not the amount of water that you are holding back. IIRC you have to plan for a "100 year" flood event. Your local NRCS office should be able to provide that information to you for no cost.

I must admit that most of this is over my head. The exsisting watershed is 109 acres according to ther topo map. They want us to cut a swail to lower that to under 100 acres. Most of the ground 98% or more is in grass. There is a small stream feeding the pond that is normally not very much volume and even dries up some summers.
They did send me some work that gives some of this information but it is all greek to me. This is the same report that gave the reccomendations to get the pond lowered to a C4 rating. Those requirements were to lower the dam 4.4' lower the water level 2.15' and lower the emergency spillway by 3.6'. The exsisting emergency drain runs through the bottom of the dam (high pressure concret pipe) and has a control valve located inside the dam accessed through a manhole.They want us to drain the pond so that we can run a camera the entire length of that pipe and then add an upstream control to it. That is the main reason I want to add a siphon system so we do not need to do that. The exsisting overflow works just fine but may require the same type of scrutiny so by adding the siphon/overflow I am hoping to eliminate the need for both inspections.

Just curious Tom how are the Crappie doing in that 4.5 pond?
(size, population, overall experience with them & if you know how long have they been in their and what type are they).
Thanks
Tums

That is a good question. To be honest with you I did not know they were in there until two or three years ago. My stepdad built the pond over thirty years ago but I was already moved away and married. I was there when they brought some of the fish which came in trucks but I was not present when the fingerlings were set out. They came in styrofoam boxes and I just remember that there were a lot of them. I also know that he put in fifty fresh water eels but no one has caught any of them for twenty years or so. There seem to be a decent amount of crappie in there and they are bigger than the biggest blue gills but I do not know what type they are.