Pond Riser Rotted Out - Fix?

[lxskllr]

The good pond at work has the riser rotted out, and all the water runs out. It's like a huge, semi deep puddle. Boss wants to bypass the riser, then fill it with concrete, but he's balking at the cost of concrete + a pump truck to deliver it. My idea is to chuck a bunch of rubble down the riser to plug it up, and use the bypass. It won't be perfect, but it should silt in over time. It would be higher in wet weather, and lower during drought, but in any case, I think it's better than the water all rushing out.

Any downsides to that idea? The biggest I can think of, is you end up having to do it right, and you're stuck with a ~10' column of rubble that has to be dealt with. Also, the riser could completely bypass, and the water undermines the pipe through the dam, and you have the rubble pile to deal with, but at that point, your looking at driving sheet pile, and excavating with a trackhoe. Probably what it would take to fix it right, so nothing lost?

Is rubble down the riser a good idea?

[Southside]

Could you sleeve it with a slightly smaller one, then concrete between the two instead?

[lxskllr]

Not sure how you could join them. There's a vertical component, and a horizontal. Either one by itself could be sleevable, but I don't know how to join them without excavating the whole thing.

[Southside]

Cut an upside down "U" into the bottom of the vertical so that when it drops down to the horizontal it sits on the bottom, the "U" allows water to go from the vertical to the horizontal.  You need to seal just above the "U" so the concrete won't slump down into the horizontal but I have to think there would be a way to inject foam or something into that void.  Or you could use an inflatable bladder to fill the horizontal, set the vertical onto that, then deflate the bladder and pull it out through the horizontal.  

[Mike W]

what about bentonite?  has that been considered? not fully picturing the situation, but bentonite is used for pond liner and sealing leaking liners of other types as well, just another thought and a lot cheaper then the concrete and pump costs.

[lxskllr]

Right now, I'm just speculating. I've been clearing a lot of brush around the pond, and it would be easier if the pond were at the proper level to keep brush from growing. Completely selfish  :^P  Not completely. The pond would look a lot nicer it were full, and that's been the reason for my clearing crusade. It started with cleaning up some dawn redwoods that were getting abused by vines, and I kept going cause I want to see the place look like something.

Boss mentioned the bypass, and I've been getting on him to start work, or at least start fleshing out the idea. That part's basically free aside from labor, and would have to be done first anyway.

No one was there when the pond was constructed, but you typically have a clay lined dam. In this case corrugated metal pipe was used for the riser that sits vertically at the water line, and should have a trash rack on top, but I haven't seen evidence of one yet. As the pond fills, it drops down the riser to a horizontal corrugated metal pipe where it goes through the dam and outfalls to a stream. The riser has rotted out so the lip of it is lower than the design spec, and of course the pond level has dropped accordingly. It can also be assumed the pipe going through the dam has rotted out too.

The proper fix would be draining the pond, or perhaps driving sheet pile, excavating the dam, and replacing everything that's rotted out. That's expensive for a what amounts to a big land ornament used by a single private party. He's talked to some other farmers that mentioned filling the riser with concrete, and adding bypass pipes through the dam. That's where all that came from, and I'm pushing to start making that, or something happen.

The bentonite is an interesting idea. I'm gonna explore that a bit, and see if that would be a good fix  :^)

edit:
The way I typically fix something is just do it. I do the easiest, cheapest, least destructive fix I can do as proof of concept, then adjust as necessary. Sometimes it works fine as-is. Might be a little hillbilly looking, but the important part is it works. My concern with this, is a hillbilly repair might cause bigger problems or more hassle to correct. Just about anything aside from doing it right has to work the first time, or there could be issues. Hence asking here. One thing I like about this forum is the members have a long and wide range of experience(That's a nice way of saying you're all a bunch of geezers  :^P  ), and might have seen some of the successes and/or failures in person  :^)

[doc henderson]

what is the cross sectional size of the pipe?  what is the length.  maybe a flex polyethylene pipe and pour concrete around it.  unless it is a huge volume.  does water still run out the end of the pipe.

[lxskllr]

Going by quick eyeball and memory, I want to say it's 24" pipe. The outfall is in a big clump of stickers I haven't gotten to yet; might be 30' from the riser. Water's going down the riser. so it's almost certainly leaving the outfall. If not... That would sure make the problem more interesting  :^D

[luap]

What would it take to drain the pond and replace the riser? You could  feed an 18" plastic pipe trough the 24" and join to a new riser with the pond drained. Just thinking out loud here.

[lxskllr]

The pond's fed by a couple small streams, so water's always coming, but not a huge volume. A big pump could probably handle it, but big pump rental is big $. I'm not good at eyeballing area, but I want to say the pond's 2ac, with a .5ac island in the middle, so 1.5ac*1' deep as a guesstimate?

[btulloh]

Put in spillway then plug the riser

[lxskllr]

Put in spillway then plug the riser

That was my first suggestion. He didn't like that cause of erosion. I think if it were lined with riprap it would be ok. Sufficiently armor the outfall, and it would be a long time before anyone had to worry about it.

[Ed_K]

 I use to build impoundment in Tx. and all the one we did had a collar joining the thru pipe to the riser. You could unhook your riser and if the thru pipe is rotted a little cut it back some an replace the riser. I wouldn't try to fit something into what you have now, as the thru pipes where engineered to a certain water flow. And the one we put in were always to the smallest they could get away with. Now a days an engineered flow of 100 yr flood is not good enough.

[Wudman]

Let me send you a family of beavers that has the pipe plugged in one of my ponds.  I need to "remove" them, but I have a lot of respect for the industrious creatures.  They don't cause too much trouble here in the Piedmont, but raise cane on stuff down in the flat ground.  In this case, I have been removing dam from the spillway every week or so.  We have an acceptable level of water in the pond and we are maintaining the status quo.

On your pipe issue, we had a similar problem many years ago.  We rented a property and raised tobacco on it.  It had a small pond.  We laid irrigation pipe to the field one afternoon and several of us kids decided to take a swim after we finished.  One of the participants, pushed off of the riser in the pond and it broke in the 90 degree angle at the bottom.  This was a 6" galvanized pipe. We brainstormed for a few minutes on what to do and decided to plug the pipe.  Dad ran back to the house and grabbed the chainsaw and sledge hammer.  He cut a cedar pole about the size of the pipe.  He drove a foot long piece into the pipe.  That temporary repair lasted about 35 years before the remainder of the pipe gave up. 

A 24" pipe would present a little more of an issue to plug but could be done.  We have a low water bridge near us that has a number of 24" culverts.  (build by the CCC back in the '30s).  We used to go down there as kids to swim.  A piece of plywood to block the inflow side would make for a nice swimming hole.  It can be done.

Wudman

[Sixacresand]

Assuming it is an earthen dam, I suggest hiring a hydraulic excavator to dig out the rusty metal horizontal pipes and riser, fill and pack dirt/clay to back fill the dam.  Then put in a PVC siphon overflow assembly and in the top of the dam and an emergency overflow or run-around nearby in original ground to handle storm water. 
   My day job used to be designing sediment ponds for mining.  Too many things can go wrong with risers and horizontal pipes buried deep in a dam:  leaks,  float ups, beavers, etc. Best to keep everything high in the dam for maintenance.  All metal pipes, galvanized or not will eventually rust out, cave in and wash out.  

[lxskllr]

Thanks for the ideas everyone. Some sound more expensive than I think boss would be willing to pay. I'll mull it over a bit, and run them by him. I'd like to see something done. The pond's too nice to let it turn to garbage.

[lxskllr]

Figured I'd update this...

Since making this thread, beavers have moved in and blocked the riser. The pond's now overfilled, and draining through the emergency spillway(I didn't know it had one). I've never seen it look better. Blue heron and egrets have moved in, and it all just looks a little nicer.

Downside is the beavers have cut down some trees I liked, especially the bald cypress. Boss had someone get rid rid of a couple beavers, but more remain. I was irritated at first, and volunteered to go after them with my shotty, but it's hard to complain about the results. I've also found that wrapping the trees in filter cloth dissuades the beaver from chewing. Super easy, and I doubt it would take me more than an hour to wrap all the "keeper" trees. Boss just complains, and threatens to remove the beavers. Trying to keep that from happening, and I want to scavenge some cloth to get the trees taken care of, and the boss quiet. I'm pretty sure we can all reach an agreement and deal with each other. The beaver can have the crappy trees, and the wildlife and humans get a nice pond that can be enjoyed. The outcome's been almost ideal imo.