Pond Boss Forums POND CONSTRUCTION Building a dam Need help fixing a dam.

My father-in-laws dam broke and we are looking for suggestions.So, after fixing the dam twice it broke again last year. His place got 10 inches of rain in less than 24 hours and it took the damn out. from the looks the spillways were taking all they could handle and the water sarted rushing over the dam a eroded it a fast rate. Im not sure of how big of area the watershed is from but it's quite large there is three creeks that meet in the middle of the "Lake". We have a few ideas as far as redoing it. We are thinking about doing a concrete "spill over" in the middle of the damn somwhere so if the water riser 5-6 inches over the drain pipe it will then go over the spill over then to the spillways. We have also had trouble getting the grass to take on the dam so I'm thinking erosion mats are going to be a must. So we are looking for suggestions and also possibly trying to get someone to come take a look at it. we plan on doing all the work ourselves again. By the way it is located in southern Alabama in Crenshaw County. Here are some pictures. Thanks ahead of time!!!

http://i868.photobucket.com/albums/ab250/tjenkins0421/dam021.jpg





[img]http://i868.photobucket.com/albums/ab250/tjenkins0421/dam014.jpg[/img]
[img]http://i868.photobucket.com/albums/ab250/tjenkins0421/dam013.jpg[/img]
[img]http://i868.photobucket.com/albums/ab250/tjenkins0421/dam012.jpg[/img]

Tyler:

I'm not a dirt guy, but I'm sure that some experts will be along by tomorrow evening.

Have you tried talking to the local NRCS for dam construction tips and help on correctly sizing the emergency spillway for the watershed that you have?

10 inches of rain coming down 3 creeks would clobber most dams. Sorry to hear about the problem(s).

How large is this body of water?

Do you have any kind of emergency run around?

How was the dam repaired in the past?

I believe it is a total of 18 acres when done. There are emergency spillways on each side of the dam. The dam was just rebuilt and a spillway added to the otherside because there was only one spillway before.

Wow Tyler those photos really tell the story. Sorry to see such damage to your pond. If it were me I would contact Mike Otto. Mike is one of the top pond builders in the US. I think it would be well worth it to have Mike take a look at your pond, spillway and dam.

You can find the contact info for Mike Otto and other pond builders in the Pond Boss Resource Guide... Pond Construction, Pipes and Other Pond Hardware.

Tyler,

Essup's correct in stating what your first step should be contacting NRCS to see if they can do an engineering design for you. They can determine the watershed area, calculate the projected amounts of runoff for various amounts of precipitation, and design the structure so it would be able to handle that amount of water.

It is truely amazing to see how much water can flow through a watershed after a heavy rain. About a month ago we had 5 inches in 4 hours and all our NRCS designed dams functioned properly. All the dams except 1 were able to pass all the water through the principle spillway (tube). The other dam had water flowing through the secondary (earthen) spillway for a short period of time.

I'm assuming that your dam was constructed based on what "looked" good based on normal flows. One of the pics seems to show a fairly narrow emergency spillway. On our dams the principle spillway tube is designed to handle a 25 year storm by itself. Thus they range from 18 inches up to 4 ft in diameter. There are at least 2-4 ft of elevation from waterlevel to the emergency spillay elevation. This ensures that the tubes can flow completely full before the water reaches the emergency spillway. Then there is another 3-4 ft of elevation from the emergency spillway to the top of the dam. The emergency spillways are between 10-30 ft wide and have a slight slope down the backside to the existing creekbed. We get sod forming grass like brome grass growing on the emergency spillway. Then when water flows over it the grass lays over and protects the soil, much like a thatched roof.

If NRCS can't/won't help, try to get an engineering firm to look it over. It would be interesting to see what they say. Based on what you describe you might need several large principle spillway drop structure tubes (3-4 ft dia) with a couple feet of elevation up to the emergency spillway. Then a spillway 30-50 ft wide with another 4-5 ft up to the top of the dam. It is easier to overbuild a dam, rather than keep rebuilding the same one.

Bill

b

Tyler,

I think the reason that you haven't seen much more feedback is that all anyone at a distance can do is speculate on what might work. Without topo maps, information on soil types and vegetative cover in the watershed, and runoff estimates from various precipitation events, one cannot give any firm solutions.

As I said, what you need is to get a local NRCS person or a private engineer on the site to do this work. It may cost you some dollars, but it would be far cheaper than re-building the dam. Who knows, you might have your dam placed in a location where it is not feasible, unless it is tremendously overbuilt to handle the three creek flowing into it. At least that would be my gut feeling, supported by the fact that it has washed out several times. To handle that water flow you might need a very large concrete spillway (or many large drop inlet tubes) along with 5-10 feet of freeboard up to the emergency spillway, and then another 5-10 feet up to the top of the dam.

Bill

Bill, thanks for taking the time to provide great feedback.

Thanks Bill. I can give general suggestions, and point someone in the right direction, but engineering via photographs from roughly a 1,000 miles away is impossible.

Thanks for the feedback. After re-reading my post I kinda came off as an ass. It wasn't meant to sound that way. Who at NRCS would you talk to? Engineering?

Tyler, I don't know how large the county NRCS office is in your county, but in mine there are 3 people in it. I'd just stop in and tell them your problem and let them run with it to see what they have to say.

The level of help (expertise) that you get from them will vary from little to none to someone that thinks out of the box and bends over backwards to help. My county has the former, and a NRCS office two counties over is the latter. Too bad that they don't cross county lines to help.

Nope.

No worries Tyler. I'm sure you're just frustrated by the situation, after looking at the photos I sure would be if I were in your shoes.

Get an expert on the ground to look at the situation and post their conclusions and recommendations for some additional expert feedback.

Tyler, In our county we have both the county NRCS office as well as a regional office. The regional office has the engineers who do dams, lagoons, etc. Just give the office in your county a call and they should be able to direct you to the right place. It seems like it varies around the country.

Worst case, if the NRCS doesn't have the personnel or ability to do the work, there should be some engineering firms in the area. They would cost you something (compared to it often being free with NRCS). The other thought would be to see if the US Fish and Wildlife Service has any offices close to you. Up here they have a "partners in wildlife" program where they can provide technical assistance as well.

Good luck,

Bill