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#315224 12/22/12 06:33 PM
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Need some opinions from the experts... In the process of building basically a new dam / pond... Dam is nearly finished, contractor wants to put in a 18" overflow pipe in addition to the spillway. Is this absolutely necessary? The only really good location for the overflow pipe is about 30 feet from the spill way and the backside of the dam is kinda steep there which will be an erosion issue and I really just don't really want the pipe. Is it a bad thing to have water trickling over the overflow on a continual basis?? Then when we have a substantial rain having a large amount of water flow over the spillway??


7 Acre +/- pond. Stocked with CNBG, RESF, GS, TFS, FHM, in March - June of 2008, Stocked with 200 3" F1 Tiger Bass in March of 2010... Additional stockings of CNBG, Tilapia, FHM in May of 2011.April of 2012 and May of 2013.
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Is the spillway the only overflow for the pond if the pipe isn't installed? Is the spillway concrete or dirt?

If it's the only overflow, the pond should have a regular spillway or pipe for water to exit during normal rain events, and an "emergency" spillway. If water is constantly trickling out the dirt spillway, it'll slowly eat a channel in it.

Regarding pipe going thru the dam. Could you put a liner or geotextile fabric where the pipe ends, and then put rip-rap on top of the liner/fabric to prevent erosion? Or, 45° the pipe and add more so it dumps on the ground at the very base of the dam.


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Yes, Spillway is the only overflow period. So I like your idea about the liner, rip rap or 45... will look into that. So looks like I will go with the pipe as the overflow and the spillway as the emergency. How much above the pipe should the spillway be??


7 Acre +/- pond. Stocked with CNBG, RESF, GS, TFS, FHM, in March - June of 2008, Stocked with 200 3" F1 Tiger Bass in March of 2010... Additional stockings of CNBG, Tilapia, FHM in May of 2011.April of 2012 and May of 2013.
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Quick question. How much land do you have behind the dam?

Extending the bottom of the overflow pipe another section or two might be an option.


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Not to much..dam is along my back property line


7 Acre +/- pond. Stocked with CNBG, RESF, GS, TFS, FHM, in March - June of 2008, Stocked with 200 3" F1 Tiger Bass in March of 2010... Additional stockings of CNBG, Tilapia, FHM in May of 2011.April of 2012 and May of 2013.
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Pinetar, if you haven't read the threads that I list below, you should. There's a lot more than just sticking a pipe thru the dam and letting it stick up in the pond:

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=253695

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=272310

I'd double check with the NRCS office to make sure the pipe is sized correctly. I wouldn't want to think about having to pull it out and installing a larger one. They'll have the information to size it correctly, and to give you the correct freeboard dimension. There should be 2 measurements that are critical in building a dam. I think they are Primiary Overflow pipe to emergency spillway and emergency spillway to top of dam. There's a formula for the depth and width of the emergency spillway too, so it's sized correctly. You don't want water going over the top of the dam during a 100 year rain event.


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Met with NRCS to discuss freeboard, spillway, overflow pipe, emergency spillway, etc, etc. Jest of it is they recommend by the book having a overflow pipe, spillway and 100 year rain event emergency spillway. How practical this is and how much this is actually put into practice by your average joes who have a pond and a budget is another question... I know my frustration will show through a little here, but it seems all these wonderful guidelines are written and engineered by someone who takes not a care to being able to build a project like this on a reasonable budget.

I would rather spend a little extra now and not have issues with a leaking overflow pipe 15 - 20 years down the road. I am already having to build this second "super pond" to account for sloppy work done when this original dam was built prior to me owning this property.

Met with my builder and a consultant. Consultant is adamant against an overflow pipe as "they are a leak that will eventually happen, regardless of anti-seep collars etc". Builder can be swayed either way...

The plan we are considering (at substantial additional $$$$) is to skip the overflow pipe, use the planned spillway as the overflow and construct / excavate a 500 foot ditch that will engage at the 100 year flood event, line this ditch with rip rap etc.... This ditch will shed into my back 40 (if ever used).

Couple of my concerns are of course the additional funds... (probably the ones I have allocated to use for my aeration system) and how much of a maintenance issue is this ditch going to be? If we line it with rip rap, I wont be able to mow it, so its going to be a bunch of spraying etc to keep it from becoming a snake den, etc.

I just am having a real hard time even considering digging through this awesome dam we built to put a pipe through it...Been a lot of blood, sweat and tears put into this and digging through it at any level to put this pipe in just chaps me big time!!

Any thoughts??

Last edited by Pinetar; 12/27/12 01:05 AM.

7 Acre +/- pond. Stocked with CNBG, RESF, GS, TFS, FHM, in March - June of 2008, Stocked with 200 3" F1 Tiger Bass in March of 2010... Additional stockings of CNBG, Tilapia, FHM in May of 2011.April of 2012 and May of 2013.
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My initial novice thought is a spillway that is not built properly (and used like an overflow pipe) will be alot more headaches and repairs than a overflow pipe that will give out in "X" number of years. A big question would be how often is the overflow pipe expected to be used? Will it be a constant flow thru or once a year?

I have seen some lakes/ponds, mostly gov't built, that have a spillway that is used non stop, like a common overflow pipe. But, most of us do not have the money to build it properly so that there is not yearly troubles with it.

Have you considerd a siphon drain?

Personally, the funds to do it right may be more than you thought intially. The dam is a permanant part that is needed now. Put the money into it now, if needed. The aeration can wait till you save some more up in a year or two. Not as crtical of factor like the dam. Wait and see what others will say on this.

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After reading the thread I am not seeing how big the pond is and how large is the watershed topography. Smaller ponds in my area commonly have plastic overflow pipes (4"-8" dia) that are laid horizontal and buried around 12"-24" below the ground embeded in the free board as the pipe leaves the pond. Water is drained to a ditch or another outlet tile.

Outlet pipe structures are intended for releasing water from common rain events. Most spillways are for emergency high water surges. Siphon pipes are good for fish, weed, and shallow shoreline management.

A wide, deep high water earthen or cement spillway designed with proper slope and soils for the velocity of watershed water could be used for your pond if budget is critical. It is easier and cheaper to plan and design a spillway than fix one. Devote good money to better spillway design and construction, rather than the outlet pipe structure. Spillways have a tendency to erode, wash out, get perforated by digging burrowing animals. A wide well built stabilized spillway IMO, would handle more water release than a outlet pipe structure. A larger volume spillway IMO should have rip rap or cement on both sides to help reduce any possible water movement causing erosion during high water events. A cement sluceway on the back side of the dam, if the spillway in on the dam, might be appropriate. The emergency overflow spillway for my pond is not on the dam.

The drainage ditch to move water from your water spillway would not have to be ripraped the entire length; just riprap until the water is . It could be grassed and have gentle sloping sides (4:1 marginal - 5:1 better) where you could mow it or keep the brush out of it (slow sloped surface ditch).


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I second what Bill said. But, pay attention to the "A wide high water spillway could be used for your pond if the pond is not large and it doesn't have a huge watershed." part. If the velocity of the water is relatively fast, it will erode the spillway, causing you to spend lots more $$ to fix the problem.

What sise pipe did the NRCS recommend? Tell us what they said in regards to sizes of freeboard, etc., etc.


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Thanks...just seeing your responses means a lot!! Pond will be approx 6 - 8 acres when full pool. NRCS said 3 foot free board minimum and 18" overflow pipe. They did not give me specifics on spillway or emergency spillway in regard to height and width. So in regard to wide high water spillway... what is wide? 20 feet, 50 feet, 100 feet??

Bill in regard to the pipe setup you were discussing utilizing it in the free board. Would you still use an anti seep collar?

Last edited by Pinetar; 12/27/12 11:19 AM.

7 Acre +/- pond. Stocked with CNBG, RESF, GS, TFS, FHM, in March - June of 2008, Stocked with 200 3" F1 Tiger Bass in March of 2010... Additional stockings of CNBG, Tilapia, FHM in May of 2011.April of 2012 and May of 2013.
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I added some things to my above comments. Reread it. Size of spillway will depend on watershed and if a horizontal outlet pipe is used. Anti-seep colars are a very good wise investment on outlet pipes especially if you want the water level to ever be above the exit depth of the pipe. Aquatic ecosystems sells anti-seep collars that fit various sized pipes. Two or three would provide good anti-seepage insurance. http://search.aquaticeco.com/index?D=Ant...nti-seep+collar

Using betonite mixed in with clay packed around the exit pipe is good cheap, leakage insurance. If you don't use an outlet structure I would spend a little extra money to get an oversized better built spillway. For spillway design talk to someone knowledgable about the specifics for your pond and watershed. If it was me I would get two or threee reliable experienced opinions. Good or the best available technical advice should be similar in nature. Subjective opinions and guessing will vary in content.

Some of my information above came from the pond planning and building book - "Perfect Pond... Want One" by Bob Lusk.
http://www.pondboss.com/store.asp?c=8

Last edited by Bill Cody; 12/27/12 11:56 AM.

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It's a shame that you have to scramble now to get it done right, but at least the construction isn't finished yet. You probably have some time left to take a step back, do a little more research on what's the correct way to build it. Even if it takes a trip or 2 back to the NRCS, it'll be worth it in the long run not to have to touch the dam/overflow pipe/spillway again after everything is seeded and growing.

I agree with Bill on the 4:1 marginal, 5:1 better. You can seed the "ditch" if you decide to go that route with a seed mixture that is for water retention basins or areas that get flooded occasionally. That way you won't have to cut it, just minor annual maintenance to keep the brush/small trees from growing there.

On the spillway, I'd make sure that you put down some erosion mats to help keep erosion down to a minimum while the plant seeds that you spread out get established. Once erosion starts, it's a PITA to fix. Make sure the contractor triple checks that it's packed down and level. You don't want the water to concentrate on exiting the pond at one point on the spillway - that point will be the most susceptible to erosion.


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Here are some tips about outlet pipes and spillways from articles by Mike Otto - Pond Boss Texas Best Pond Builder: “Some ponds can get away without an outlet pipe, but don’t run the risk. Analyze your watershed from an engineering perspective and verify. Pipes are necessary to not only rid your pond of extra water but to help with management. Pipe size is determined by the amount of water to run through it.” ‘Moving Excess Water’ –Mike Otto in Pond boss Mag: Sept Oct 2004.
“A Spillway Is A Spillway Or Is it?” M.Otto Pond Boss Mag: Nov-Dec 2004. One acre 1 inch deep contains 27,000 gallons. This will give an idea of water volume from a 10” or 12" rain on your water shed acreage (27000 x acres). The spillway needs to handle this water volume. Spillways work best when water flows wide and shallow.
“Emergency spillways are designed and engineered for an orderly exodus of big rains, torrents, floods. Before a spade of dirt is turned you should have a solid grasp where the spillway should sit, how large it should be, and where it directs excess water. Spillways can be made of concrete, earth, rock…. butt design and materials should be well thought out and engineered to the specific situation. Earth spillways should have the most gentle slope possible to allow water from the biggest rain possible to move as slowly as possible. If water gets over the dam you will likely repair or build a new dam. Dirt spillways are cheapest but expect maintenance and erosion. Heavy vegetation allows water to soak with less runoff. Best place for a spillway may not be at the end of the dam. Look for a natural spillway location and consider mechanical or concrete in the design because water is directly released where it needs to flow. Without a good spillway all good features of a pond or lake could be lost in one big rain event.“

Back issues of PBoss magazine are available here:
http://www.pondboss.com/store.asp?c=9

Last edited by Bill Cody; 12/27/12 09:46 PM.

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Some more info on spillways from another PBoss article.
From: "Spillways .... Avoid The Flood" by Mike Otto. PBoss Mag Nov-Dec 2007. Mike discusses spillway options for excavated ponds and ponds with dams. Here are some pertinent points from the artcle.

Spillway pipe is the principal or primary spillway. When the primary spillway cannot drain all the water, the pond fills to the secondary spillway called the emergency spillway whose job it is to quickly release huge amounts of water during heavy rains. The excess water should always flow through the spillway and not across the top of the dam. Excavated ponds are usually dug on flat ground and do not have spillway pipes because massive amounts of water in these ponds drains across the top and out, not downward through a pipe or over a dam. How do you wash out just a hole in the ground?. However most all ponds have some sort of dam unless the pond is built on very flat ground where the water fills the hole and out the top.
Reasons for a spillway pipe are: 1. Water management –release of bottom water or water drawdown. 2. Manage ordinary rainfall and protect emergency spillway from erosion damage. The emergency spillway should not be on top of the dam unless the spillway is rock or concrete. Small terrace can be used to divert water away from the backside slope of the dam . Thus if any erosion damage occurs it is to the spillway and not the dam.

Last edited by Bill Cody; 12/27/12 05:33 PM.

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That is alot of good info above. I have thought about Pinetar's comment about how the consultant is adament against overflow pipes. If it was me, I would ask for ponds that this consulatant was in charge of and go visit them. See how he built the spillways, and are they built properly. What does his theories look like after 10/20 years. What do the owners think. He may do a really good job, or it might make you aware that you need to really watch the situation closely and impart the knowledge shared above.

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Siphon Diagram: http://www.ponddampiping.com/syphon1.html

I think this kind of shows what Bill is talking about with regards to the drain being in the top part of the dam.

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Originally Posted By: Pinetar

The plan we are considering (at substantial additional $$$$) is to skip the overflow pipe, use the planned spillway as the overflow and construct / excavate a 500 foot ditch that will engage at the 100 year flood event, line this ditch with rip rap etc.... This ditch will shed into my back 40 (if ever used).


Just so you know a 100-year event has nothing to do with 100 calender years. It is a term to describe the 1 in 100 chance of getting a set amount for a set area in a given year. I was in a meeting about storm runoff this year where it was said in my area of Alabama a 100-year event occurs about every 3 calender years now. I always get nervous when people use the term 100-year event and (if ever) near each other. The 100-year term is very misleading since in you life time you are more likely experience one.

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Thank the Insurance companies for the new definitions wink laugh

It's a term to describe a 1% chance of crap going crazy at any time shocked

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That is a really nice looking set up. Any ideas on what size pipe you would use for this? Is the pipe that goes in the pond and down the back of the dam buried under the surface or is it on top of the ground.

So if I am looking at this right, this is an overflow pipe and a siphon all built in one. Am I correct???


7 Acre +/- pond. Stocked with CNBG, RESF, GS, TFS, FHM, in March - June of 2008, Stocked with 200 3" F1 Tiger Bass in March of 2010... Additional stockings of CNBG, Tilapia, FHM in May of 2011.April of 2012 and May of 2013.
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Originally Posted By: Pinetar
That is a really nice looking set up. Any ideas on what size pipe you would use for this? Is the pipe that goes in the pond and down the back of the dam buried under the surface or is it on top of the ground.

So if I am looking at this right, this is an overflow pipe and a siphon all built in one. Am I correct???


The way I understand it, and someone correct me if I'm wrong:
--Size of pipe is the same as what size is recommended for your pond's overflow pipe.

--It can act both as an overflow pipe and siphon, depends on how it is set up. Thats the true benefit of it.

--If you want it to act as a overflow pipe, the horizontal pipe is placed in the dam at the level you want the surface water to stay at. Then it still can be used as a siphon when needed.

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Originally Posted By: JKB
Thank the Insurance companies for the new definitions wink laugh

It's a term to describe a 1% chance of crap going crazy at any time shocked

If I remember the way the USGS person there said "it just means there is a 1% chance that the 63% chance of 100-year event happening to you occurs this year".

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PineTar if you do not have to buy your pipe right away there is an upcoming auction in Dothan, Al. that may have what you need for alot less. I have bought quality used & new pipe there several times. Last year I picked up some 12" construction leftovers I needed for about 1/3 the cost.

Deanco Auction
16th Annual January
Farm & Construction Equipment
Public Auction

Thursday, January 31st to
Saturday, February 2nd, 2013 - 8:00am
Highway 431 N • Dothan, AL
Sale Site Phone: (334) 693-2540
Sale Site Fax: (334) 693-2551
Main Office Free: (334) 677-3192
Main Office Fax: (334) 671-0149

PLEASE NOTE: The buyers fee is 10% on the 1st $2500 then 1% on the remaining balance of each item.

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Found this while cruising thru some of the archives. Siphons..

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=126193#Post126193

Has a nice link included to a photo installation. Lots of reading.


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