I’m looking to put river rock (depending on size) around the shore of my pond to help erosion. Very little waves, pond is in the woods, but I’m looking to avoid erosion and soggy edge. Likely will have some grass planted on top of bank if I can get it to grow in the heavy shade.
Question is how far into the water should I put the rocks to prevent erosion and secure the bank line.
Slope is generally 3:1 throughout, a little steeper on one small side of the pond. Waves will mostly be from light aeration underwater and surface.
River Rock? Hopefully you are talking about larger than river gravel sizes. I suggest a range from 1" to 12" rocks, mostly on the larger side of that range.
I went from a foot above the full pool water line (diagonally up the bank) and 18" below (vertically downward wrt to water depth). This works well as my pond has not dropped more than a foot during any dry spells. Consider your water fluctuations and apply rock appropriately. I'd give it an extra foot below the lowest water level. I do have to admit that it seems like the rock that is normally exposed above the water has crept into the water some as the last 4 years has gone by. I guess it's settling and, maybe, sliding down the back some, but this can easily be added to compared to adding rocks at the under water side.
Having rock below that 18" mark (down into 4 foot of water) in several places will also be good for the smaller pond inhabitants if you can spare the rock.
The problem with steeper slopes is that it will want to migrate to the bottom faster than you'd like. I still stand by the 1-12" rip-rap, but you need something to slow the effects of gravity on the rock. I have steep banks along two sides of my pond and have not added rock there, but I believe I have few choices...
1.) Drive stakes into the under water slope at about 1.5- 2 foot down and then add 10" tall hog/cattle wire (or something to act as a rock barrier like hedge limbs, timbers, or pipe...or whatever). Then start placing the rock up from there until you get well above the water line.
2.) Just add rock where I want it and add more as it moves. At places along my banks, a rather round 10" rock will roll on down into the abyss.
3.) OR, add rock all the way down to where the slope levels out more. The rocks become their own barrier.
All of which are very labor intensive, hence the reason I have no rock there. I would start with the larger rock (6-12") and then come back with smaller rock (1-2" clean gravel). This smaller rock will fill in the voids and help lock in the settling of the larger rock and give extra protection to the exposed soils in the voids.
Not so steep slope in the first pic. This was my efforts at adding rock to the dam and you can see that the rocks further down the slope are large, some 18", while the ones further up get smaller. This row of large rocks is supposed to help keep the rock from migrating down into the pond. I doubt it was needed, but I was doing this by hand, one rock at a time and I thought "why not?".
Finished with a gravel bed...
The far bank in the below photo shows my steep banks. If you step into the water there...you'll be up to your neck in 2 more steps given that you do not slip. Then you'll be under water in a spilt second...lol
Here's a couple after it was full. You can see in the last photo that the bank was undercut before the pond was renovated and it is about a 2 foot drop into the water and, I would guess that both sides of the pond are near a 1-to-1 slope for better than half their lengths.
As far as limestone is concerned...I guess it depends on the water chemistry. It could help some pond's pH while hurt others.
Thought maybe I would see some Yellow Iris shoots near the water's edge, QA!? ; ) I will be doing a little experiment myself in a couple weeks with bank erosion and repair of muskrat damage in one or two pond bank locations. To address rock sliding, I'm going to place large retaining wall blocks in about 2' depth water at the base of the bank in about a 30' long section. Just a single row, no stacking. Then dump limestone slag above the retaining wall block. I'm not trying to rip-rap the entire pond bank, just the section(s) where muskrats previously dug into the banks. I consider the Yellow Iris part of my erosion control strategy, but not the major contributor. Retaining wall block is too expensive IMHO for larger applications, but since I'm focusing on one section only that covers 30 to 40' of the bank, I can live with that limited expense. Again, trying this as a first experiment with the pond at full pool. I've already placed some slag along this pond bank section about 18 months ago, so I'm attempting an even stronger barrier with block and stone. I suspect the retaining wall block are a bit harder (not much) than standard cinder block with regards to being submerged. I guess I'll find out in a few years. I'm actually hoping the limestone slag improves the water pH and alkalinity since I struggle with suspended clay silt in our pond too. Not expecting miracles though...
CD, I think QA's guidance would be less expensive and just as or even more effective than my experiment in erosion control. BTW, if you pursue rock or limestone, be careful to specify ROCK and maybe not SLAG. I thought I was getting rock and instead got slag that's rock, broken concrete, brick and block fragments. My concern would be not knowing where the slag originated from. It could have contaminants on surface and/or absorbed. Any of which might leach out into your pond water. Good luck on your project.
Your rock option looks real pretty and would be a benefit, but I would get some larger rock too. Adding larger rock in the 6 to 12" range (50/50 mix with the 2-6") will be better for steeper slopes. These larger rocks will help keep your investment from migrating towards the bottom of the pond. Look at my 1st and 3rd pic...you can see that I ran a row of larger rock first in deeper water and then added the smaller rock uphill from that. This row of larger rock acts like a barrier to the smaller rock.