needing ideas on the primary overflow control for about a 5-6 acre pond I'm building earthen dam, approx 18' high in center, base will be maybe 60-75' wide at center
Put in a large metal culvert with a spillway at one end of the dike so if it overflows it won't wash out the dike, also make a pull plug style metal drain so the pond can be drained to work on it rather than dig the dike out if repairs are needed to the pond or you need to clean it. Thats how we do all ponds in our area anyhow.
Yair...monkey. I don't quite grock what you mean by "primary overflow control" but with a pond like that the size of "bywash" as we call it here is governed by the catch area and possible rainfall. Formulae would be available from your State irrigation Dept. I mostly cut the bywash on one end of the wall and set out to have about three feet of freeboard above that level. It should be cut perfectly level and despite what the formulae may tell I like to cut it as as wide as practical and construct it to direct the water away from the toe of the embankment. The aim is to spread the water and to slow it down and if you can establish some sort of grass/vegetation so much the better...on domestic work I encourage clients to lay sod and establish a good ground cover. Embankments of this size and a little smaller are very common here for stock water and I used to build them with a Komatsu 65. Cheers.
The pond should have two overflows... One is the level that you want the pond's level to be maintained.. say at the 12 foot mark or maybe a little higher... the emergency spillway is for heavy rain events... usually around the end, say at your 15 foot mark... Rip-rapped to prevent erosion...and continue for maybe 25' to 50' away from the dam,with a berm to protect the front dam where the emergency spillway has been built.... with some larger rip-rap every now and then to disperse the water over a larger area... Some will rip-rap the dam and shore line of the entire pond to prevent wave erosion...
by primary I guess I mean like a riser in the center on the water side of the dam I had planned on a spillway on one end for the really bad storms my plan is I want to finish up the damn THEN finish all the other work.....I want to make sure I have adequate material for the dam first. If I dont put in some type of center drain system, the pond will fill very quickly because of the ground water and rain...long before I can get finished was thinking along the lines of a horizontal pipe (galvanized culvert) with a riser to the eventual water level....leaving the horizontal section open for now (water side) till I finish...then cement it shut don't know
ahhh yeah that's what i was thinking first pond so I'm kinda playing it by "what looks right"
Hey monkey, you wouldnt need to cement it shut just put a gate valve or shear gate on the end of the pipe. Check out ponddampiping.com, it will give you a few ideas and options, you can also check out the different valves available. If you put in a conventional style thru-dam system be sure to properly install anti-seep collars, this is not a good place to cut corners.
thanks for the site, and info
Yair...monkey. Do you have a stream or ground water flowing throught that gap in the middle of the wall? If so you have a pretty difficult situation. The design of the overflow might be the least of your problems...you need to be able to control that water and how you go about it will depend on the flow. Cheers.