Ok, Here we go. Around 1987 my grandfather built this lake with pretty bad timing. 3months after it was completed they received a 16in rain in 24hrs, 13 on which was in 9hours. The lake litterally filled up and busted in the same rain. My grandfather never was able to get the funds to fix the dam before he passed away, so there has just been a huge hole there ever since. Recently I have purchased this property and want to repair the dam. We just started clearing some of the trees off of the dam. It's hard to tell how big it really is from the pics, but the trees on the dam are about 20-25in in diameter and from the top of the dam to the bottom is about 35ft. There is about 7-8ac cleared in the bottom of the lake right now, so a lot more will need to be done there.
We are currently looking at putting a large 10-12" siphon pipe in the dam as well as doubling the size of the spillway. There are 550ac of watershed on this one spot so it gets a lot of water. Any thoughts from some of those who have lakes this size?
It seems like building a large lake like this is a lot like building a house in that there are always things you are really glad you did and some things you wish you would have done differently. I am interested in hearing those comments from those of you who have experience with larger lakes. Thanks.

very cool, very large
Describe the spillway details, please.

Don't have too many specific numbers yet, as we are currently taking trees out of where the spillway washed out. The massive water blew out the spillway approx 20yds wide and approx 12ft deep, then made a small 4ft wide by 8ft deep cut through the core. At the time this was as wide as the spillway could be made because of a property line, however, I have since purchased that property as well so this will enable us to double it's width. We will have to dig into the side of a pretty steep hill to do this, so I may have to use some kind of stabilizer to keep the hill from washing back into the spillway. I have been told that we will need to cut a big wedge back in the spillway and carefully layer it back into place. Thanks for the intrest.

Maybe somebody can answer my curious question on this, and it may help you too: with trees on the dam that are 20" diameter, if all those roots rot it will be a big problem won't it? Does that mean the whole dam needs recoring?

As shown in pictures we are currently removing all trees from front side of dam. We are removing stumps and all roots. I believe dam, especially one this size will be ok if dressed and packed well. Someone else may want to weigh in on this though as I am not qualified to give advice, just my opinion.

What about the back side of the dam ? Those trees need to go as well and around 50 yards back. Don't undersize the pipe. We get more water but have a lot bigger pipe than you. The spillway is for emergencies.

As you clear the lake bottom have them make structure that matches your goals. Structure archive - http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=92463#Post92463 . Also lime the lake bottom if needed.

Assume you have a pro pond builder/engineer working on this. Matching/repair on the core is not for armatures. Lakes that size are not like digging a hole. The weight and pressure of the water must be accounted for.

Yes I do have a consultant coming in to advise. Hope to meet with him tomorrow. He is a retired NRCS with about 40yrs in building lakes. Was just mainly wondering if there were any who wished they had done something that they didn't, or wished they had done something differently. Love the links on structure. Great ideas and imagination starters.

23 acres of water? I would make the dam at least 50% tougher than spec. This ain't something that you wanna do twice. I don't have to tell you that since this is the second time that your family is doing it LOL.

Some regions of the US would require professional engineering and permits for a dam that size, including subsequent engineering reviews in the following years to verify dam integrity. If a lake suddenly shows up on the aerial strip maps that wasn't there last year (or was much smaller), you may be high profile.
If it's me, I poke around to verify what the guidelines are, and I do it very discreetly. No need to get any antennas up and quivering.

I would think the pipe needs to be 24" or 36" for a lake that size but it all depends on the watershed area.

We recently build a lake that was 15 ac and it had a 36" pipe with a 72" riser. It was built to handle 900 cfm.

..."Was just mainly wondering if there were any who wished they had done something that they didn't, or wished they had done something differently."

I think there may be a thread for that somewhere; but...

In the do differently category... I would...

complete the sediment basins / forage ponds before dam is completed

design locations and put structure in before dam is completed

plan out and implement landscaping, dock, boat ramps, beach, before finalizing dam (if absolutely certain will hold water)

ensure have primary, alternate water release means so that spillway is truly an emergency spillway only

ensure that there is an adequate drop on spillway side to prevent any undesired fish from swimming up the spillway and into the water body

talk to a lot of people to really detrmine which fish you want in the pond.

Update: All trees have been removed from dam. Prep work has been done and everything is ready for contractor to come in next week. Spillway will be a two stage. 50ft being 18in below dam and another 25ft 12in below the top of dam. The water level will be controled with a siphon pipe. Engineer says if we drop the water level to 18" below the spillway we are good for a twenty five year rain with a 12in pipe. This is because of the storage of twenty three acres and 18" of freeboard. Just for good measure im gonna put another 12" siphon pipe 6-8" above the other which will cut on while still having 10" of freeboard.
One question I have: I pulled all of the pine trees off of the dam and piled them at the bottom of the dam. These piles or windrows are about 8ft tall and are made up of 18-20in pines and at full pool will be in 28-32ft of water. Thinking about leaving them for structure. Any thoughts?
Most of the bottom around the open dam area is a shell type rock. I have actually been digging a lot of it out for a long driveway. If i do some soil tests around the shallower banks, what type of results and ph am i looking for?
Thanks for the intrests and input.

Unless aerated with a bottom diffuser, those trees by the dam on the bottom will spend a lot of time in anoxic water and be unuseable for the fish.

If you were to bring them up into water that was 12'-15', they would be more accessable to the fish all year 'round. I'll bet that without aeration you'll have a thermocline set up somewhere between 10'-15' deep during the summer.

Smart Move to put in the extra pipe, because in a 25-year storm actually has nothing to do with 25 years in hydrology.
http://climate.umn.edu/doc/misc/100year.htm

BTw I had a EPA meeting in Alabama a few weeks ago about storm run off where it was metioned that the 100-year storm (or 1% storm) had been hitting some local areas with the frequency of every 3 years.

Most of the year fall , winter and spring , the trees in deep water will work. But once it warms and they are below the thermocline the fish will not use them. I like spreading out my structure so that there is some at all depths (year round fishing). Take a look at the structure archive for more info. http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=92463#Post92463 it has pics , ideas and text on structure options.

It is a good idea to always over engineer/design your water control systems if possible.

Finally finished rebuilding the spillway and feel pretty good about it. Put in a 13' wide core to start with and found some really good gumbo clay to put in it. Spillway is 75ft wide and has 80ft of tabletop before it starts a slow taper to the creek. Had dump trucks and sheepsfoot running on it the whole time of construction. Also put a 30ft emergency spillway on the other end of the dam. The water level will be controled with two 12"Siphon pipes with 2ft of head before it hits the first spillway. (would just as soon it not ever hit the spillway.) I'll be installing the siphons this week hopefully, then time to plug the pipe running in the bottom. Main creek is flowing pretty good so hopefully it won't take too long to fill up. Will try to work on docks while it does. Did some clearing in the upper end. Made some trails where I could get around. Gonna have about 3-4ac of flooded timber in the upper end that will be about 4ft deep that should be fun to fish.

Well I'm finally back at it. Gonna go with a double 10" siphon that should go in on Friday. Will run one all the way to the bottom and the other just about 10ft under surface and stage it above the first one. Gonna put the first and water level at 2ft below spillway level.

How much water do you have now? Any new pictures??

No water yet. Pictures are pretty much the same with the exception of clearing off a point for a housepad. Have been waiting to get the siphon pipe in before plugging the hole. Really dry right now so probably fill much till fall.

This past winter it filled up to about 7acres with a 6-8" pipe running open in the bottom.

Found a ton of excellent gravel in the bottom and have been mining it for my driveway. I now have about 3500ft of road and a small parking lot (for a future pavilion area) I built using the gravel out of the bottom.

Question for you siphon pipe experts. I have the diagram and all looks good. I have been told that the pipe needs to be put in off center of the creek, then angle back to the creek on the back side. Do I need to angle the front side as well, or can it run straight down to the bottom?

I guess your planning on covering that gravel with clay in the end,? Gravels good for driveways but doesn't hold water too well

It's actually in the upper end. Really more of a iron ore rock shell stuff.

You have an interesting project going there - hope it all works out well. I'm curious about the freeboard of your dam. I would have thought that a lake of that size with over 500 ac of watershed in an area with a lot of annual rain would require considerably more than 18". I have a much smaller pond with 4' of freeboard and a 12" siphon pipe and about 35' of overflow areas on both sides of the dam. 165 ac drains into the pond which is located in NE Texas which gets considerably less rain than East and SE Texas. Heavy rain events can still bring the water within 6" of the dam top. Of course, 23 ac can buffer so much more water than my small pond can. NRCS has tools to calculate all this, so your were certainly wise in hiring an experienced consultant. NRCS was supposed to was supposed to layout my pond's dam and shoot the elevations, but dropped the project at the last minute without informing me, with dirt moving equipment already in place. They decided watershed was excessive.
I had to make an on the spot decision to go ahead without them.

I'd still seal it if you want it under water.. It could basically turn into a drain and your pond won't rise above the level of the rock..

I would take both siphon inlets to the deepest points possible for two reasons...First, to remove the worst water in the pond every time there is a draining event and second, when going into siphon mode, 11,12,20 feet of head pressure will push water out far faster than 10 feet of head pressure and with 500+ acres of watershed, volume will matter!!!

Thx Rainman. Will go atleast 25ft deep with the lake side pipe. Reckon how far that will shoot water out the other side on a 10" pipe. Any ideas on stopping erosion from force of siphon pipe water. Saw once where they turned the back side pipe straight up into a 4'x24" culvert turned up where it would hit the water and slow down. Any ideas? would this work with that much pressure?
Thanks

Wow, that sounds like a tough engineering problem. That is a LOT of water to move, least of which is the pressure of water flowing around the bends in the pipe, or the suction at various points. It has to be pipe well rated for that flow and pressures.

If you have the room for it, point the outlet straight up with a surrounding pool of water and/or concrete pad to disperse the energy. I am no expert, but that is what they do with the outflow of canal lock pipes up here which move TREMENDOUS amount of water very quickly.

I would sweat with that much watershed and a hurricane or TS heading my way. It may not happen often, but you do need to plan for the worst with that much water which could burst and harm those downstream.

The pressure is not that great (25' of water head is just under 11 psi), but the velocity when in full siphon mode can be a very powerful and destructive force at around 30-50 feet per second of flow. Shooting the stream onto heavy rip-rap or some form of non-eroding structure to let it slow and flow would depend on your particular landscape and budget.

Do this right the first time to avoid a repeat. We have much more pipe than that for lakes with what my guess is similar flow. I have redundant systems in place. First a small pipe 6 -8 inch (system 1) at full pool into the main overflow pipes which are from 30 to 50 inches. At full pool + 18 inches water goes over the top of the main pipe (system 2). Then at full pool + 2 ft an 8 - 12 inch siphon starts (system 3). Then at full pool + 4 ft the emergency spillway is active (system 4). It is 30 ft wide and has 2 more feet of capacity to the top of the dam. All 4 systems work at the same time.