How to keep soil from escaping down the slope with rain?

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z_johnq

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Hello,

Havin't posted for a pretty long while.

In my backyard, there is a very steep slope where the soil under the fence has run down with rain water so the ground under the fence has sunk. The fence posts, you can see from the pics attached, are unable to stand streight up.

I am a handyman myself but not sure if fixing the problems can be done by a DIYer. I'm happy to provide more pics if wanted.

Any suggestions are welcome!
Thanks in advance.
John
 

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Sparky617

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You need something to hold the soil in place and/or to the water into something that can withstand the flow. The challenge with this is keeping the soil in place while you wait for the grass to grow enough to hold the soil. I've experienced the joy of watching my hard work get washed down the hill when a big storm came before the grass sprouted. You'll need some sort of mat to hold the soil and seed in place or use sod. You can also create a dry stream bed using stone to divert the water. You'll need to use a mix of large and small stones, all small ones will wash down the hill.
 

z_johnq

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Hello Guys,
Sorry about the late reply. I guess it's too late to plant grass to hold the soil, Sparky617. Please check the pics attached. A huge piece of concrete/rocks has fallen down to the end of the slope. The fence won't last long since another heavy rain is coming. Wish I had talked to you guys earlier.

The first pic, backyard1, was taken at the top of the slope; and the rest at the bottom of the slope.

Snoonyb, are you saying how the fence posts were buried? They were planted in the soil with about one foot concrete as base; since the soil is loose and running away, so are the posts.

Would you think some landscaping guys can help rebuild the fence and the slope? I know it will be costly.
Thanks a lot.
 

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Sparky617

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Looking over the pictures I think you're going to need come up with a way to handle the water. The slope looks pretty steep so trying to keep grass growing will be a challenge. I'd probably look at a rip-rap gully to carry the water down the slope without washing the soil away. You could bury a culvert with a catch basin to catch the water. I'm not a civil engineer so my advise based on your pictures could be worth about as much as you've paid me to provide it.
 

ekrig

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I think that you actually have two somewhat distinct problems: (1) shoring-up the side of the cliff/slope/edge, and (2) managing the water flow to prevent it from accumulating on that edge.

Regarding 1: That's seems to be somewhat of a corner, so you'll need to provide a "structural" connection from that corner to the sides to distribute the load and provide something for wall to anchor to. Which brings to the fact that you need to rebuild that wall and have them extend sufficiently to the sides (hard to know from the pics). I'd build a rebar-reinforced concrete wall that is thicker at the base with a little bit of slope inward (think of the walls in a water damn).

Then, to address 2, I'd make the soil at that corner higher such as to divert the water toward the sides while still away from the corner, that would reduce the load on the corner and split the water flow to the side, which you should then divert with pipes or gutters down to the sides and base of the slope.

That's how I would approach it, but I'm no civil engineer either...
 

tomtheelder2020

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Looking over the pictures I think you're going to need come up with a way to handle the water. The slope looks pretty steep so trying to keep grass growing will be a challenge. I'd probably look at a rip-rap gully to carry the water down the slope without washing the soil away. You could bury a culvert with a catch basin to catch the water. I'm not a civil engineer so my advise based on your pictures could be worth about as much as you've paid me to provide it.
The idea of rip-rap it that it creates longer flow paths, therefor slowing the water and reducing erosion. The problem is that, in effect it, creates multiple narrow flow paths that, unless there are enough of them, results in eroding the soil the rock is set on. I have no idea how to determine how wide a rip-rap channel needs to be to handle a given amount of water but too narrow can be a costly waste of time. Fabric underneath can help sometimes erosion will still occur under that. Setting the rock in a concrete channel lining works great - unless soil under the concrete moves, cracking the concrete, resulting in erosion under the concrete. I have seen all of these things. I am not saying they cannot work - but I am saying over-design is your friend.

Short of a hardened channel or a pipe, the best solution I have seen used narrow trenches across the channel, filled with concrete to create underground "walls". If the concrete is poured against undisturbed soil, a flow path under the concrete is unlikely to form and the water will just flow over a series of "dams", rather like a fish ladder. The walls need to extend up the sides of the channel far enough to prevent lateral erosion (i.e. the top of the wall mimics the shape of the channel.
 

tomtheelder2020

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Z,

Erosion occurs where water is concentrated. Is there any way to grade the surface above the fence so that flow lines on the ground diverge as they approach the fence? Is there a way to collect the water before it gets anywhere near the fence? If a significant portion of the water is coming from downspouts, directing it into pipes could be the answer. Remember though, pipes just move concentrated water from one place to another. Be sure you are not creating a new erosion problem where the pipe outlets.
 

z_johnq

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Hello T,

Thanks a lot for your time and tips. I agree with you that I need to fix the water problems. But I guess the first priority is to build a 'retaining wall' to keep the soil from losing. But I don't have a flat base for the wall to sit on. I cannot do it without some heavy machinary, can I? I don't think I can build channels to lead the water where I want it to go because the backyard is a little too big to set up channels.

A friend of mine, who is a contractor, suggested building a wall before the existing fence with heavy duty wood board combined with metal screen imbeded concret. But I probably need an excavator to dig and remove the soil/rock in order to make room for the wall. What do you guys think? It sounds similar to what Ekrig's option 1.

Thanks again.
Z.
 

tomtheelder2020

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Digging a hole, or a few, is the only way to know how difficult excavation will be. I interpret most or all of the rock on the slope as having been placed in an attempt to buttress the slope. However, buttressing isn't much use against erosion. A wall might go a long way toward a solution as long as you: 1) provide plenty of drainage so water pressure does not build up behind the wall*; and 2) anticipate and control where the water will will go.

*or the wall is designed to withstand the water pressure and to prevent flow under or around the sides of the wall.
 

billshack

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I had the same problem with my back yard, so what i did was all organic material like leaves, grass cuttings, kitchen waste , and branches ect i just throw over the cliff. In time the stuff routed and started to grow , it took several years now it is very stable but looks like a mishmash of vegetation.
 

z_johnq

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Hello Bill,
I have been doing the similar things like dumping leaves down to the slope but they will not grow, and they get rotten instead. I don't expect they can grow and hold the soil from escaping.
Thanks.
 

BuzzLOL

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Rake up all the leaves and other debris. The ground leading up to the concrete needs to be above the concrete and tapering down to the top far edge of the concrete so water doesn't get against or under the concrete... then cover the ground with grass seed with burlap over it to hold everything in place for 3 weeks until the grass sprouts... watering it at first... if expecting heavy rain before grass is established, temporarily cover whole thing with weighted down clear plastic film while and until rain stops...
 

billshack

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Hello Bill,
I have been doing the similar things like dumping leaves down to the slope but they will not grow, and they get rotten instead. I don't expect they can grow and hold the soil from escaping.
Thanks.
it takes time years to be exact.
 

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