Pond Issue....

[neopheous]

I am attaching a few pics to show the conundrum I'm in right now.... it is a new pond, just built it last summer and I obviously miscalculated the amount of water coming into it as it filled the 18 overflow pipe I have and then ran over the dam.... prior to that it had already ate the overflow side of the dam up pretty good even though I had placed a LOT of large rocks on the dam. What I am planning on doing right now is to pump the pond down and then create an emergency spillway on the left of the spillway pipe as you look from the pond side. I believe this is an old logging road cut into the hillside probably 15-20 years ago so it should be solid. I was planning on just digging it out with my Kioti backhoe and FEL. I know I don稚 have much freeboard and I am planning on building the dam up some over the current pipe with the excess dirt I take out for the spillway. Although some of the dirt will also be used to fix the dam on the overflow side where it is washed out. I would like some ideas as to if this is the best way to do it without spending a fortune. I am going to create a concrete and rock tailrace under the overflow pipe as well to keep it from eating away the dam on the overflow side.
The way I see it right now I have possibly 3 options, as listed below:
1) Dig out an emergency spillway on the area marked in the pic. It is probably about 75' to the ravine from the pond that I would need to dig out.
2) Remove the existing 18" overflow and create a concrete spillway wider that goes over the dam where the pipe was and forget the emergency spillway.
3) Remove the 18" overflow pipe and replace it with a larger 24" - 30" pipe.

Any other ideas or which of these sounds the best? Thanks!

 

[John Fitzgerald]

You can get answers to all those questions on "www.pondboss.com/forums"

It looks like a case of too much watershed for the pond size, but that could be helped by an adequate emergency spillway lined with concrete.

 

[oosik]

You are asking questions that would best be answered by a hydraulics engineer who is on-site at your pond. Any way you look at it, answering this situation is going to be quite a bit of money. Do yourself a favor and seek local professional assistance.

 

[jfh28]

if you've got that much water coming into the pond then it sounds to me that it won't be an "emergency" spillway but rather a "continuous" spillway.......so the question becomes is that really where you want the water flowing all the time and are you prepared for the erosion it will cause.......I suspect the logging road will look like the pic you have at the overflow pipe in short time......I agree with oosik.....time to get some local professionals in........Jack

 

[RedNeckRacin]

One real good place to start is to get a topo map and figure out how much watershed that you have coming to that pond. draw a line connection all the high spots that drain to the pond. That should give you a good starting place to talk to an engineering firm on what kind of flows you are looking at unless you want to run hydrocad yourself.

 

[neopheous]

You can get answers to all those questions on "www.pondboss.com/forums"

It looks like a case of too much watershed for the pond size, but that could be helped by an adequate emergency spillway lined with concrete.

Ok. Thx... just posted there as well.

 

[neopheous]

if you've got that much water coming into the pond then it sounds to me that it won't be an "emergency" spillway but rather a "continuous" spillway.......so the question becomes is that really where you want the water flowing all the time and are you prepared for the erosion it will cause.......I suspect the logging road will look like the pic you have at the overflow pipe in short time......I agree with oosik.....time to get some local professionals in........Jack

Well, no, it wouldn't be using the emergency spillway all the time.... normally 90-95% of the time the overflow has handled the amount of water just fine, other than needing a concrete tailrace. However, we just went on record as having the wettest February ever recorded... so this was unusual for our area/timeframe.

 

[vlcakc]

When I had my old pond rebuilt a few years ago, the dirt contractor I hired called in the County Water Conservation Specialist for consultation. They decided on an 18" overflow pipe set 12' higher than the base of the dam, a 15' wide spillway 2' higher than the overflow pipe and 2' more elevation to the top of the dam. They got it mostly right with a couple of exceptions. The Water Conservation guy opined that he didn't think the pond would ever fill up based on the watershed size. Even the experts don't always get it right!! The pond filled up almost overnight after a 3-4" rain, and has stayed full or within 2-3' of the overflow pipe, except for a severe drought a few years ago. A few years later during an unusual 6" rain storm, a wall of water swept down the normally dry creek bed into the pond overflowing the pipe, the spillway and went over the top of the dam. There was some erosion on the back face of the dam near the top. The dam is now heavily overgrown with Bermuda grass sod, so I don't think any future overflows will cause significant damage. Calling in the local professionals is still a good idea even if they don't always have all the answers. Good luck with your project! Vic

 

[neopheous]

When I had my old pond rebuilt a few years ago, the dirt contractor I hired called in the County Water Conservation Specialist for consultation. They decided on an 18" overflow pipe set 12' higher than the base of the dam, a 15' wide spillway 2' higher than the overflow pipe and 2' more elevation to the top of the dam. They got it mostly right with a couple of exceptions. The Water Conservation guy opined that he didn't think the pond would ever fill up based on the watershed size. Even the experts don't always get it right!! The pond filled up almost overnight after a 3-4" rain, and has stayed full or within 2-3' of the overflow pipe, except for a severe drought a few years ago. A few years later during an unusual 6" rain storm, a wall of water swept down the normally dry creek bed into the pond overflowing the pipe, the spillway and went over the top of the dam. There was some erosion on the back face of the dam near the top. The dam is now heavily overgrown with Bermuda grass sod, so I don't think any future overflows will cause significant damage. Calling in the local professionals is still a good idea even if they don't always have all the answers. Good luck with your project! Vic

Wow Vic! Man, that is hard to believe there was that much water to circumvent the 18" pipe, the 15' wide spillway, plus another couple feet of insurance in the dam itself... I do not believe I would ever have that much water, but that is good to note. It sounds like it was built right, whereas if I knew then, what I know now, I would have done several things differently on mine, but now I am just trying to fix it the best way possible without completely redesigning/rebuilding the pond.... I'm afraid if I have to do that I may just fill it in and put me a nice pool in for 30K....

 

[vlcakc]

Wow Vic! Man, that is hard to believe there was that much water to circumvent the 18" pipe, the 15' wide spillway, plus another couple feet of insurance in the dam itself... I do not believe I would ever have that much water, but that is good to note. It sounds like it was built right, whereas if I knew then, what I know now, I would have done several things differently on mine, but now I am just trying to fix it the best way possible without completely redesigning/rebuilding the pond.... I'm afraid if I have to do that I may just fill it in and put me a nice pool in for 30K....

I wouldn't have believed it either, if I hadn't seen it with my own eyes! I think the design mistake they made was the location of the spillway at the far side of the pond from the creek channel. The creek channel enters the pond on the extreme South side and the spillway is on the North end of the dam, perhaps offset by 60-70'. I think if the spillway had been more in line with the channel, most of the overflow would have gone out there instead of over the top. Live and learn from our mistakes! Vic

 

[skipperbrown]

4 years ago we had what the experts are calling a 500 year flood. Hundreds of home that were not in a flood zone were flooded (and got no, zero, nada insurance reimbursement for their flood damage. The flood opened my eyes to what can happen when you get too much rain. Make sure you can handle at least a 100 yr flood and also be cognizant of what might happen downstream if your pond releases all its water at once. You could be held liable for someone's loss/damage of property or livestock. I would start with a call to your county extension agent.

 

[MossRoad]

If it overfilled with an 18" overfill pipe enough to top the dam, then you need a larger overfill pipe for starters. You had no emergency spillway, either. There should always be an emergency spillway. You're putting one in, but what do you know about sizing it? And the overflow pipe, too, for that matter. As others have mentioned, best to consult an expert, especially if there's anyone else's property downstream that could be impacted if your dam breaches.

 

[neopheous]

If it overfilled with an 18" overfill pipe enough to top the dam, then you need a larger overfill pipe for starters. You had no emergency spillway, either. There should always be an emergency spillway. You're putting one in, but what do you know about sizing it? And the overflow pipe, too, for that matter. As others have mentioned, best to consult an expert, especially if there's anyone else's property downstream that could be impacted if your dam breaches.

Thanks.... concerning the mention of should the dam fail in the last couple of posts, and what is downstream... There is the main creek that runs along the road (dirt, with very little traffic... if I am at the property for 8-10 hrs I may see 2-3 cars and one of those is the mail carrier.) That creek/road is about 75-80 yards from the dam, and then downstream of that I own along the road on the pond side for probably close to a 1/2 a mile. Beyond that it is just pasture for the next 2 miles... the pond is approx. 1/4 acre so I am not too concerned should it fail and where the water goes, as it should just flow to the creek and empty out from there..., other than I definitely don't want it to fail!

 

[MossRoad]

Just be aware of the power of moving water.....

Here's a horror story from a 3 acre beaver pond that broke...

Flood waters rush in Duvall after beaver dam break | KOMO

 

[neopheous]

Just be aware of the power of moving water.....

Here's a horror story from a 3 acre beaver pond that broke...

Flood waters rush in Duvall after beaver dam break | KOMO

Understood, although that it at least 12x larger than my pond, possibly more depending on the depth, not to mention sitting evidently right above homes..... plus a dam built from sticks and logs plus a little bit of mud rather than compacted clay.... but I do realize even those sort of dams have failed before.

 

[philbuilt]

Do you have the option to put the spillway on the other end wa
Where the water is coming from. That would solve 2 issues, one water level controll and you could remove your over flow pipe. That’s how I controll my pond. High side inlet creates consitant water level and prevents lower dam washouts. If that’s not possible eliminate the pipe and do a wide and long spillway with integral creek bed

 

[neopheous]

Do you have the option to put the spillway on the other end wa
Where the water is coming from. That would solve 2 issues, one water level controll and you could remove your over flow pipe. That痴 how I controll my pond. High side inlet creates consitant water level and prevents lower dam washouts. If that痴 not possible eliminate the pipe and do a wide and long spillway with integral creek bed

Phil, I wish... but I do not see anyway since it is all higher elevation... see attached below:

 

[philbuilt]

Can you give us a google earth image? Your spillway will work as you have it in the pictures just make sure it is wide and a slope of 1/8” per foot. Water needs to move over it but not fast. Make sure to grow grass to help eliminate washout. I’m a fan of natural drainage not pipes. Put a small creek bed in the spillway and get rid of that pipe. Looks to me like you could raise the water level another 18”.

Just my thoughts
Phil

 

[rekees4300]

There should always be an emergency spillway.

DITTO ... No matter how much it rains the water must NEVER top the dam or it will be like a knife slicing through hot butter. In addition to proper overflow pipe sizing, pipe blocking from debris needs to be prevented. I use a device called a bar guard.

View attachment 543778

 

[neopheous]

Can you give us a google earth image? Your spillway will work as you have it in the pictures just make sure it is wide and a slope of 1/8” per foot. Water needs to move over it but not fast. Make sure to grow grass to help eliminate washout. I’m a fan of natural drainage not pipes. Put a small creek bed in the spillway and get rid of that pipe. Looks to me like you could raise the water level another 18”.

Just my thoughts
Phil

Phil, I like that idea as well. So, let me make sure I understand what you’re saying. So the emergency spillway that I have highlighted is that what you are saying should be 1/8 in drop per ft? And I had already planned to immediately sow it it with perineal rye grass and fescue. But you also mention removing the pipe and making a spillway there also over the dam in its place? That’s a much steeper drop and I see no way to make a slow descent. I was just going to make a concrete and rock tail race under the pipe. Or are you saying just remove the pipe and build up the dam in its place and then use what I call the emergency spillway as the sole outlet for the pond? If so I would assume it needs to be at least 10’ wide, plus b/c of the lack of freeboard I have it could be close to 2-3 ft deep by the time it reaches the ravine that I plan on running it to.