Pond Boss Forums INTRO Questions & Observations Emergency spillway erosion...

Water went over my emergency spillway for the first time a few days ago. MAJOR erosion despite pretty well established grass

I know that something must be done. Two or three more events like this would undermine the whole dam!

Any suggestions? Concrete? Rocks?

Good article covering your problem in Pond Boss Magazine Mar/Apr issue, page 48.

A pond owner I met stopped this problem by putting about a ton of steel shavings from a machine shop in his emergency spillway. He had previously tried bagged concrete. The shavings are heavier than concrete and kind of interlock together. You could probably buy at scrap steel price, now about $100/ton. I know it's a wild sounding suggestion, but it works very well. His pond has excess watershed.

Frank, sorry to hear that. We have seen some crazy rain amounts last years spring and this year. What do the big boys say ?

Tracy

I have concrete over our spillway. At times, we have 2 feet of water flowing over it. Works like a charm! Definitely not the least expensive route but if you want something there that youll never have to worry about then its a for sure fix. Alternatively, you could probably put some large (4-5in) rock but once again you risk it not being enough

Thanks for the advice, guys. I've scheduled a meet with my construction guy, looks like concrete would be best. Got a pretty big watershed for the size of the pond, and a creek that flows constantly regardless of the weather.

John F, I assume the steel shavings were mixed into the concrete to make it heavier & thus more stable, right?

On the plus side, the water has cleared up, vis now about 24 inches. Fish are feeding very well, I can see different sizes of BG and FHM. And button bush are growing like gangbusters, what a plant for shoreline and erosion!

I know a person would have to have the topography to support it, but my overflow pipe is actually in the drainage ditch that feeds my pond. once my pond is full and starts backing up the drainage ditch, it can flow out the side of it.

Small pond, and probably not something most folks can do, but seems it would avoid a washout of a damn.

Sean

Erosion is caused by the speed of the water flow. If the emergency spillway can be made wider and the drop (slope) reduced, the erosion will be minimized if the speed of the water flow is reduced. If the speed of the water flow isn't reduced, it has to be lined with something that won't erode, and something that the water can't get under. Some concrete spillways have had undercutting issues from water falling off the concrete at the end, removing soil, and working it's way back under the concrete.......

I agree about the good article in the magazine.

No, the shavings are not embedded in anything, and are in a wide row across the spillway a few inches deep. The water percolates through them. Beats anything I ever saw for erosion control.

Anybody use them? My dirt guy wants to use rip rap in the spillway to stop further erosion, but from what I read gabions (chickenwire) keep the rocks in place much better during a water event than just individual rocks.

Feedback?

FWIW they had to replace the patio at our new place due to cracks. When they tore up the first effort they produced large broken slabs with many still connected by the reinforcing wire. For me, it was a PITA cause I wanted to use the broken slab in the pond as habitat and spent hours clipping and removing the reinforcing wire. In your case, the broken up stuff with the wire intact might be just the ticket. Some of my pieces were 100+ pounds each and the wire should work the same as chicken wire but last a whole bunch longer. A call to a few concrete contractors might get you broken slab for free....maybe make it a little bit prettier with a thin layer of large rip rap on top......

Just a crazy idea....

I've seen some pretty big rip-rap washed away in an emergency spillway. I've never seen the gabions washed away.

Put thick geotextile fabric (available from WhiteCap Supply) under them to prevent the dirt under them from being washed away, if that happens, that might allow the gabions to drop down or move around if their "foundation" is moved.

Thanks!