Thoughts on stream bank erosion, threatening structures.

[fastline]

Just visited a job I'd rather walk away from but I think we all agree this is just a bandaid job. What we have is a stream or creek that is dangerously close to a dwelling. Governments just don't care, of course. During extreme flooding, the stream swelled up to capacity, which took many feet from the sides. We are talking 10ft from the structure right now!

I warned that continually adding soil on the bank will never work, we agree on that. Right now we are just adding riprap at the bottom to stop lower level erosion.

We are talking about a bank that is mostly clay/loam, nearly straight down about 30ft. Slight slope but just not enough. They might not lose any more until another major flood but in that case, it will likely get into the dwelling.

I have done many things, but never saving a structure from an eroding stream bank. We have build serious retaining walls for overpasses, but on a budget of more than this entire property. I am trying to think of a strategy that can help this guy!

 

[skyking1]

I'm sorry, but go with your first assessment. it is usually the correct one.
With a steeper stream bed in softer material, you can't add enough rock to make a difference. It will just rinse around that rock, and sometimes the backside wash is worse than if you had just left it alone. Your rock placement ends up midstream and diverts the water AT the bank you are trying to protect.

 

[Bluox]

You might think the government don't care ,as soon as you start mucking around a stream there will be no less than10 outfits show up and cover your donkey up with enough stop work orders ,summons and tickets to keep you busy for the rest of your life trying to stay out of the poor house.
Bob

 

[fastline]

Apparently there are letters and emails all the way to fed level saying they don't care. I want copies. I think parties realize throwing all this rock probably won't buy much time and that will be in the contract.

But curious if anyone has tried to save one? I've only dealt with stuff like this on bridges where we have access to drive pilings.

IMO, he really needs the group with the Army to do the math here. I get into geotech engineering but not this deep. This guy already knows he is going to lose his house, or part of it.

 

[Spud_Monkey]

Hate to say but the owner should of seen long ago building or buying a house near a stream or creek near a house, it's like those who build beach cabins on the beach and cry when next hurricane takes the place. How about the homeowner instead look at the costs to move the house far away as possible to buy more years till they figure out what to do next and save up money.

 

[The Peej]

gabion erosion control baskets https://gabion1.com/gabion-erosion-control/

 

[grandpa]

I did a job a few years back in a Minnesota river which is highly regulated. The fix they allowed was to cut trees down leaving the cut about six feet above the stump. We then used an excavator and pushed the tree shaft of the stump into the bank leaving the root ball facing the stream. It actually worked. It stopped the bank erosion completely. It was a relatively cheap functioning fix.

 

[Nige]

gabion erosion control baskets https://gabion1.com/gabion-erosion-control/

This....

 

[Tinkerer]

Is the stream maintained or regulated by the Corps of Engineers or The US Coast Guard ?
If it is, a permit from the Corps may be needed.
fastline; I sent you a PM.

 

[aighead]

I can only speak from the experience of my small creek but I know when there is a real good rain it's absolutely amazing what water can do. My creek is only a few feet wide at most and not more than 2 feet deep except in a couple places and it's washed bigger than basketball sized rocks around and removed lots of material from my bridge, that is normally about 2-3 feet above water level. This whole deal would sketch me out! I like the idea of baskets full of rocks, that seems most appropriate to me.

 

[Delmer]

It's not hopeless, rivers are easy to move, with enough money. You might be right that the house is not worth it in the end.

If it's loamy soil, I'm assuming you don't have heavy rock flow in the flood water? That changes things.

Another huge factor is how much land does the homeowner have access to for fixing this damage? Always call this fixing the damage from the last flood. Fixing damage is often allowed. Altering a stream is practically never allowed.

For the exposed soil, dump some topsoil over the edge, spread some fertilizer and plant it to reed canary grass right away. Unless you're planning to add soil to the bank. The topsoil can come from onsite, doesn't have to be expensive. Or, a manure spreader could "mulch" it effectively, but you might get weeds growing. The reed canary spreads by rhizomes and forms a dense sod that resists washing out extremely well. It is also competitive once established and will kill out the weeds eventually, slow to establish though.

 

[fastline]

I was going to look for recommended vegetation as I feel it would thrive in this soil and be the easiest way to stabilize the area. I am going to look at baskets but the bank slope, after the last shear event, is steep. He wants to lay some areas back, which will work, but near the home, that is not possible.

To do this right, I really feel sheet piling is the right answer, and before there is more soil loss! However, the area is TIGHT. Like I was trying to figure out how to get my machine in there. A crane won't be operating there.

 

[Tones]

Yes to the Gabion baskets but don't place parallel to the flow. Place them on an angle into the flow so they flick the water away from the bank. It also creates a backwater that will eventually silt up.

 

[cosmaar1]

I was going to look for recommended vegetation as I feel it would thrive in this soil and be the easiest way to stabilize the area. I am going to look at baskets but the bank slope, after the last shear event, is steep. He wants to lay some areas back, which will work, but near the home, that is not possible.

To do this right, I really feel sheet piling is the right answer, and before there is more soil loss! However, the area is TIGHT. Like I was trying to figure out how to get my machine in there. A crane won't be operating there.

Sheet piling might be the answer but your price in doing that is going to be way more then the house is probably worth. To have someone mobilize, buy materials in today’s market, and spend a few days doing it, you are probably looking at 250k+

not to mention they won’t go anywhere near that house with the machine as it will shake the crap out of it.

 

[Raildudes dad]

Move the house, either back from the bank or onto a different parcel of property. You couldn't hire a house mover a couple years ago on the lake Michigan shore in MI. They had more than enough work moving lake front homes back from the eroding sand bluffs.

 

[KSSS]

This is where the answer lies. We do this using the baskets or large rocks for a little more nature look. You can divert the flow of water away from that area, then rip rap the edges with a combination of larger and smaller rock and because of the diversion of water, the rip rap will stay. Common strategy here.

 

[fastline]

I think we can protect from low level erosion easy enough, but as I mentioned, this channel is about 30ft deep and she filled nearly all the way up during a flood event. The bank is so steep that setting baskets, or even just rocks is not possible. They will just roll down. And if they didn't today, they will be gone in the next flood.

Because I am not willing to dive into the civil engineering to save this house, I really think vegetation will be extremely helpful on the high bank areas. I spent some time on the phone/web trying to find vegetation that is most suitable. Canary was mentioned above but all talks online are about how to get rid of it as it seems to be very invasive. I guess that could be good and bad.

I hear what people are saying about the impact zone around pile driving. I agree! And I don't think these people have a budget that even approaches a proper repair!

My general approach might otherwise be to drive piles approx 50ft away from the structure, which would basically be in the water, then bring mountains of dirt in and backfill everything from the piles on towards the home. Effectively reestablishing a new bank.

We had thoughts to drop down concrete retaining wall blocks but I can't even get a hoe close enough! He talked to someone with a long reach but with all the trees, I don't even think that is possible. So limited on what you can do, and limited on what equipment you can even use! Talk about a problem! You could engineer a solution till you are blue, but without access to the repair zone, it's nearly impossible!

Obviously I am just wasting my free time pondering because I like to help people. Anything I do is a 'try' but I cannot guarantee it. It would be REALLY nice to talk to an Army engineer to see what they might dream up, but they are my paid government, you know how that will go.....Ironically my old boss, who we built municipal bridges under, IS a former Army engineer, but I just can't waste his time on this. Unless possibly he wants to do the job!

 

[fastline]

I did a job a few years back in a Minnesota river which is highly regulated. The fix they allowed was to cut trees down leaving the cut about six feet above the stump. We then used an excavator and pushed the tree shaft of the stump into the bank leaving the root ball facing the stream. It actually worked. It stopped the bank erosion completely. It was a relatively cheap functioning fix.

I'd like to understand what you described better. There is a big Burr Oak tree right in the middle of this mess. My plan was to have him cut anything that was hanging over the water, helping the tree fall in, but otherwise keep the tree. However, the root system is largely already exposed and I am shocked the tree is still healthy! But when the roots die, they will rot and leave canals. Its hard for me to picture this working long term but like to understand it better. This is not something I deal with commonly.

 

[Tones]

You can also build a rock Groyne in the same manner as I described for the baskets. Biggest face rock from a quarry is good.

 

[treemuncher]

How about ground anchors securing cyclone fencing to the face of the slope and then getting the vegetation started to lock it in? Gabion baskets at the base would be ideal to lock in the bottom of the fencing and protect against normal flows. Any access to scrap concrete slabs or very large rock would also be helpful.

A few years back, I had done a small project for a homeowner that was trying to stop face erosion on a slope. I think that the most cost effective approach that I found was the ground anchors (DuckBill Anchors) that you drive into the bank and then on pull back, they flip around to lock into place. It's the way most utility pole anchors are set if they don't use the screw type anchors. These are often set in with a small vibratory hammer or on an excavator mounted unit.

Something along the lines of this smaller system: