I looks pretty rocky. The truth is the problem will continue until you stop using that ‘trail’ as a drainage ditch. I had a similar problem and fought it in every way until I read US Forestry Service road maintenance instructions. Every public road you have ever driven on has had drainage along the sides and pipes running UNDER the roadbed. Water is never diverted onto the road bed. An incredible amount of water is going down that slope during a thunder storm. As soon as water finds a way across the roadbed it will erode it at an accelerated pace. I had several 4” PVC pipes feeding into ‘catch basins’ that had 14” pipes passing the water under my driveway. And those 14” pipes were barely enough to handle the flow.I've got a trail that runs up the side of my mountain. It's badly eroded in one spot, I wanted to fill it in before it makes the trail impassable. It's washed out on the downslope side, and it's extremely steep. Not sure if I'd even be able to get up it on foot. View attachment 3682140
Initially I drove 4 metal t posts into the side of the mountain, parallel to the trail. I had some 6x6 fence posts from a fence I'd taken down, so I laid them down against the t posts. Then filled the whole thing in with dirt.
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(The one t post at a wonky angle was too bent to drive in properly, but it's too steep to get down and pull it back out so I just left it. Not really doing anything to support the posts)
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It looked great for about 4 days, when a heavy thunderstorm rolled through and the t posts failed. View attachment 3682144
My next attempt I'm thinking of increasing the amount of t posts, and then using rocks to fill in the bulk of the space with dirt added as a filler. The thinking is less diet to hold water means less weight for the bulwark to support. Does anyone have any better ideas or suggestions on how to build this before I go rappelling down the mountain to get the posts that washed out?
Only posting since I said I was going to post a photo...I don't have photos but can get them later this week...
My guess is the OP will be dealing with lots more rock and may not be able to pound in "T" posts as far as they should.
This is essentially what I’m planning. The water bars are completed, but unfortunately I will be doing lots of hand digging while tied off, then the gabion. Will be a couple weeks before I am able to get back to it.I went through all 5 pages. In the first 2 pages is what you need to do.
The water bars on the top section to keep water off the trail to start with are a good start.
To repair the washout you need to install a water bar just above the washout to prevent your work being undone. I recommend you aims the waterbar flow onto tree roots to prevent a new point of scouring.
Actual repair: Can you get a "zero swing" digger up there? Something in the 6-10 ton size to have the reach and weight. If not you have some hand digging to do.(pick, shovel, and mattock, literaly.)
Suggest you make a flat floor and use gabion wall. Do job in "lifts" (layer of fill) and at each lift extend the lift further into the trail. This is called "keying in" for long term stability.
NOTE you must bring the repair up to enough above the trail level to prevent water running over the repair.
You may have to reshape the trail camber to stop water running to the repair point and wrecking the job if the water bar just above the repair does not work.
Also I recommend you put a drain on the inside of the trail and at a point below the wash put install a culvert, where the water can not create a new scour out.
I have a steep track like yours (metaled)and is 30 degrees (measured), at the steepest part. Average grade is in the 15 - 20 deg range.The waterbars are 30 - 40 yards apart, with a drain on the high side and culverts as required.
This is what is reqired to keep my track in good condition as it provides acess to 1/2 my farm.