Pond Issue....

[neopheous]

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

I have looked at these and plan on purchasing one if I leave the pipe in the dam.

 

[MossRoad]

Good grief.... you have an earthen dam and earthen spillway. You NEVER want water flowing over the dam OR a spillway. The spillway is for EMERGENCY overflow only to try and prevent the dam from washing out if its topped. That's why the spillway is supposed to be very, very wide and completely level, and a much longer, gentler slope than the dam. Your main device for controlling the level of the water behind the dam is your pipe. You can build a box with a drainpipe in it, and control the level of the pond with boards on the box. Or you can add spacer rings to the top of the pipe. But you want that pipe to be able to handle any and all water that comes into that pond so it leaves the pond fast, and the level of the pond never ever approaches the spillway. You do not want water on the spillway ever. It's for emergencies and a last-ditch device before dam breech.

From the looks of your topo map, and the size of the pond indicated, you have a HUGE, steep, watershed above your pond. Just 1" of rain on one acre of land that drains entirely into that 1/4 acre pond has the potential to raise the water level 4". How many acres drain into that pond? Let's guess at 5 acres for an example.

A 1" rain on 5 acres will give you 5 inch acres of water.
Compress that to a 1/4 acre pond, and you have 20" of potential water level rise in an hour (assuming the ground is saturated and nothing soaks in).

Now let's assume you have no drainpipe.
And your spillway is 10' wide.
You're going to try and drain 20" of water from 1/4 acre through a 10' wide path in an hour without washing out any dirt...... think about that.

You want that drainpipe sized to control the pond level, and you want it large enough to handle a 100 year rain in your area, whatever that may be, on the watershed above your pond, however many acres that may be, and then size the pipe larger than that plus a 10% fudge factor for safe measure. The spillway is to safeguard against anything more than a 100 year rain that the drainpipe won't normally handle.

Now that is not scientific, I have no idea if its correct. And I have no idea if that's what you should actually do. I know my father always planned our yard drainage around 100 year rains, and we had 2 of them when I was a kid, and our yard didn't flood and the neighbors almost lost their houses to washouts. Our town just had a 500 year flood a few weeks ago, and everything was planned on 100 year floods. Many folks lost a lot.

Plan ahead and you most likely won't have problems. Good luck in your project. Get some professional advice.

 

[neopheous]

Good grief.... you have an earthen dam and earthen spillway. You NEVER want water flowing over the dam OR a spillway. The spillway is for EMERGENCY overflow only to try and prevent the dam from washing out if its topped. That's why the spillway is supposed to be very, very wide and completely level, and a much longer, gentler slope than the dam. Your main device for controlling the level of the water behind the dam is your pipe. You can build a box with a drainpipe in it, and control the level of the pond with boards on the box. Or you can add spacer rings to the top of the pipe. But you want that pipe to be able to handle any and all water that comes into that pond so it leaves the pond fast, and the level of the pond never ever approaches the spillway. You do not want water on the spillway ever. It's for emergencies and a last-ditch device before dam breech.

From the looks of your topo map, and the size of the pond indicated, you have a HUGE, steep, watershed above your pond. Just 1" of rain on one acre of land that drains entirely into that 1/4 acre pond has the potential to raise the water level 4". How many acres drain into that pond? Let's guess at 5 acres for an example.

A 1" rain on 5 acres will give you 5 inch acres of water.
Compress that to a 1/4 acre pond, and you have 20" of potential water level rise in an hour (assuming the ground is saturated and nothing soaks in).

Now let's assume you have no drainpipe.
And your spillway is 10' wide.
You're going to try and drain 20" of water from 1/4 acre through a 10' wide path in an hour without washing out any dirt...... think about that.

You want that drainpipe sized to control the pond level, and you want it large enough to handle a 100 year rain in your area, whatever that may be, on the watershed above your pond, however many acres that may be, and then size the pipe larger than that plus a 10% fudge factor for safe measure. The spillway is to safeguard against anything more than a 100 year rain that the drainpipe won't normally handle.

Now that is not scientific, I have no idea if its correct. And I have no idea if that's what you should actually do. I know my father always planned our yard drainage around 100 year rains, and we had 2 of them when I was a kid, and our yard didn't flood and the neighbors almost lost their houses to washouts. Our town just had a 500 year flood a few weeks ago, and everything was planned on 100 year floods. Many folks lost a lot.

Plan ahead and you most likely won't have problems. Good luck in your project. Get some professional advice.

MossRoad, I'm sorry if I have offended you with my stupid questions... but the reason I am asking is b/c I don't know.... I KNOW water is not to go over the dam, what I was trying to clarify was if he meant that I remove the pipe and build a "concrete" spillway over the dam that continues down the dam and into the stream/creek that the pond is currently emptying into. I grew up on a fairly good size lake that has a concrete spillway and water flows over it 95% of the time.... Yes, there is drain tubes, but even with water flowing thru those there is still water flowing over the dam/concrete spillway almost year round except for winter when they lower the lake for homeowners to do dock maintenance.... so I assume if it is built as such on a pond it would work the same way, I guess based on your answer that is not the case.

But to make everyone here issue a sigh of relief, I called my local Soil, Water Conservation District this AM and have now sent them pictures and a description of what I would like to do to get their input. They are going to try and come out in the next couple of days as I am taking the next couple of days off work to use my 300GPM pump to hopefully pump the pond dry until I can come up with the best solution. I guess it seemed to me that it would have some pretty cut and dry solutions such as add a bigger pipe, or another one the same size beside the current one, build the dam up some, add an emergency spillway, and build a concrete tailrace for the overflow..... but I guess somethings seem to get more complicated the more folks you get involved. Thanks for all of the assistance to those who replied and now I guess I will let the "pros" figure it out.

 

[MossRoad]

MossRoad, I'm sorry if I have offended you with my stupid questions... but the reason I am asking is b/c I don't know.... I KNOW water is not to go over the dam, what I was trying to clarify was if he meant that I remove the pipe and build a "concrete" spillway over the dam that continues down the dam and into the stream/creek that the pond is currently emptying into. I grew up on a fairly good size lake that has a concrete spillway and water flows over it 95% of the time.... Yes, there is drain tubes, but even with water flowing thru those there is still water flowing over the dam/concrete spillway almost year round except for winter when they lower the lake for homeowners to do dock maintenance.... so I assume if it is built as such on a pond it would work the same way, I guess based on your answer that is not the case.

But to make everyone here issue a sigh of relief, I called my local Soil, Water Conservation District this AM and have now sent them pictures and a description of what I would like to do to get their input. They are going to try and come out in the next couple of days as I am taking the next couple of days off work to use my 300GPM pump to hopefully pump the pond dry until I can come up with the best solution. I guess it seemed to me that it would have some pretty cut and dry solutions such as add a bigger pipe, or another one the same size beside the current one, build the dam up some, add an emergency spillway, and build a concrete tailrace for the overflow..... but I guess somethings seem to get more complicated the more folks you get involved. Thanks for all of the assistance to those who replied and now I guess I will let the "pros" figure it out.

I apologize if I came across that way. I was "good griefing" at people suggesting you don't need a pipe, not at you. It's one of the reasons I would prefer face-to-face conversations... I don't come across well in written word. Again, sorry for the gruffness on my part.

 

[neopheous]

I apologize if I came across that way. I was "good griefing" at people suggesting you don't need a pipe, not at you. It's one of the reasons I would prefer face-to-face conversations... I don't come across well in written word. Again, sorry for the gruffness on my part.

No worries... been there done that as well.... I appreciate your input.

 

[Tigershark]

We recently built another pond on our farm and I would always recommend an emergency spillway over on the side so you don't compromise the dam. Usually our pipe handles things fine but we had a week where we received close to 20 inches total and 6 inches in 2 hours and we had so much runoff the pond went over the emergency spillway for the first time, it did it's job and the dam was fine. If you cored the dam (hopefully) I wouldn't even think of replacing the pipe it is large enough you just need a spillway off to the side that handles emergencies, it doesn't need to be concrete because it will probably seldom get used. just regrade it after it washes some dirt out when water does manage to over. Pondboss is a great website been a member for a longtime.

 

[neopheous]

We recently built another pond on our farm and I would always recommend an emergency spillway over on the side so you don't compromise the dam. Usually our pipe handles things fine but we had a week where we received close to 20 inches total and 6 inches in 2 hours and we had so much runoff the pond went over the emergency spillway for the first time, it did it's job and the dam was fine. If you cored the dam (hopefully) I wouldn't even think of replacing the pipe it is large enough you just need a spillway off to the side that handles emergencies, it doesn't need to be concrete because it will probably seldom get used. just regrade it after it washes some dirt out when water does manage to over. Pondboss is a great website been a member for a longtime.

Good to know... yes, I have been discussing this on pondboss as well... in fact this was my last post there just to do an update here:

Ok.... I decided to reach out to my local Soil, Water Conservation District folks for some more ideas.... I hope to have them come out in the next day or so as I will be using my 300GPM pump to hopefully pump the pond dry until I can come up with a solution.....

But, one of the things they mentioned after I spoke with them and sent them the pics is that I need approx. 25" of freeboard above the pipe, (which I knew I needed at least 18"), but when I asked about putting a bigger pipe in they said this one could possibly handle the watershed but b/c of the low freeboard there was not enough hydraulic head pressure to allow the pipe to run at full capacity... does this make sense. or sound right?

Also in building up the dam, I know it would be BEST to have a dozer or tractor with a sheepshead roller.. BUT, since I do not have either... Do you think I could add to the dam with just using my tractor and backhoe, and then using it's weight to compress the soil? It weighs between 5500 and 6000 lbs with the backhoe. The SWCD folks said you should only layer about 6" at a time on the dam and then compress it, which sounds right... just didn't know it others have built their dams just using the weight of the tractor to compress it. I am running R4 industrial tires on the tractor as well. Plus I am a little concerned at building it higher but not being able to make it much wider... of course if all here feel it would be better to just hire a dozer for a day to build up the dam and repair the it then that's what I will probably do... although I am still not sure if I do not want to put at least a 20" or 24" pipe in place of the current 18"... would hate to go to all that trouble of building up the dam to accommodate more freeboard and then find out that the 18" with a anti-vortex plate and more freeboard still is unable to handle the watershed.

 

[neopheous]

Just heard from the local SWCD folks... just as an update:

I again talked with our engineer, and I also figured the acres of watershed for your pond. So with not being at your pond site before, the numbers are rough estimates. I came up with 32 acres of watershed for the pond. From that ran some numbers and the CFS (cubic feet per second) for the watershed for a 2 year storm would be 23 CFS, and for a 10 year storm around 47 CFS. So with that being said the 18” diameter pipe you currently have installed in your pond would carry the normal 2 year storm with anti-vortex hood. However you would have the need for an emergency spillway as we discussed earlier on the phone in the event of a larger storm. Also I would recommend extending the existing pipe further without any angles because the angle would cause a reduce of flow in the pipe. There would also be the need to increase the elevation of the dam to meet the required head pressure for the 18” pipe to flow full (which we talked about on the phone). See attached for hooded inlet drop structure form to better explain. Again the numbers are rough estimates. I will try to make it out to your pond site around 10:00 if that works for you.

 

[John Fitzgerald]

Most ponds in this area of one acre or less do not have any overflow pipes, only gently sloped, grassy or riprap covered spillways. I've never seen or heard of a quarter acre pond with an overflow pipe. That a really small pond.

 

[RedNeckRacin]

Most ponds in this area of one acre or less do not have any overflow pipes, only gently sloped, grassy or riprap covered spillways. I've never seen or heard of a quarter acre pond with an overflow pipe. That a really small pond.

it has nothing to do with the pond size and everything to do with the drainage area that feeds it.