How to fix mountain washout

[MACflyer]

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.

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.

(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)

It looked great for about 4 days, when a heavy thunderstorm rolled through and the t posts failed.

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?

 

[Topzide]

Drive t post in further to hold better. Place them closer together for support. Rocks, cinder blocks and concrete chucks would all be good choices.

 

[John_Mc]

I'm trying to think of something more substantial than T posts to use as supports. They are not designed to support any significant side load, so there is a chance that even if you get them driven in far enough so the won't rip out, the posts could just buckle. I'm not coming up with anything off the top of my head that would go in without heavy equipment to install it. Maybe the galvanized pipe they use for posts on a chain link fence? (I've seen people use Black locust posts for their high rot resistance, but they had an excavator to dig the holes for them). On my own trails, we don't have anything so steep on the downhill side, so can get away with just burying logs parallel to the edge of the trail.

Whatever you end up with, one key to a long lasting trail is getting the water off the trail before it has a chance to build up velocity and damage the trail. When we are putting in trails on a side hill, we always outslope the trails toward the downhill side a bit so that water sheds off of them, rather than running down along the trail, building up volume and velocity until it does damage. If the water is coming down in force from directly up the hill (rather than coming down the trail), you should focus on spreading and slowing that flow and/or diverting it to somewhere where it can't do that sort of damage.

 

[old and tired]

I don't have photos but can get them later this week... Drive the post down deeper, use MORE "T" posts, use wood cross ways and back fill with dirt and rocks but most importantly, don't let water run down this area again, build it up higher than the rest of the area, give water areas to drain before and divert water past this area.

Do not let water run down where the "T" post are!!!!

I have an area (I'll post photo later) that was a gully that I filled in, 20 years ago.

Later...

 

[deezler]

Seems maybe you are focusing on how to armor that area to handle big washouts, instead of preventing the washouts in the first place. Make sure no draining water can blast that area and then your modest repair jobs should hold up better.

Ditches on the upslope side into culverts or armored waterbars, etc. Tell the water where to go first, instead of letting it tell you the easiest way and then trying to fight the damage.

 

[deezler]

Do you have an excavator or a backhoe you can use or borrow?

 

[Fixastuff]

Slight off camber trail slope and rolling grade reversals are needed for a trail to be sustainable long term.

 

[MACflyer]

Do you have an excavator or a backhoe you can use or borrow?

I have a backhoe attachment for my tractor, but it only reaches about 6 feet.

 

[deezler]

I have a backhoe attachment for my tractor, but it only reaches about 6 feet.

Thats plenty for digging drainage ditches, waterbars, etc.

Probably the way my brain would work to armor your eroding section is with some BIG rocks, boulders, concrete chunks, etc. Dig enough of a pocket into the downslope into native soils to retain them firmly, then pack it all up with rocks so heavy that some rain wash can't budge them, and gives a nice big footprint for widening the trail atop. But again, first focusing on making sure water doesn't go off the trail in that spot.

 

[2manyrocks]

I'm curious how your road was carved out of those boulders on your mountainside in the first place. That's pretty impressive.

It looks to me as if water picks up a lot of velocity coming off the top of the mountain before it arrives at your road where it then starts looking for the low point to continue running down the mountain. Over the long term, water always seeks the path of least resistance. So it hits your road, probably runs down it a bit, and then has started eroding this one particular spot.

The reason the fill failed is because all that wet dirt pushed against the fence posts like 5' long levers that could be only anchored maybe a foot in the ground. This is like trying to build a retaining wall...too much force being exerted against the top of the wall caused it to fail.

If you compare this washout to the other land nearby, the washout is a vertical drop off unlike the section adjacent to it that is more gradual and banked with trees that support the road.

One of the challenges with trying to build up the eroded section is that fill material will want to roll off the mountain.

Not saying this is the way to stop the erosion, but first step would be to try to divert the water somewhere it doesn't continue to wash this soft area away. Then you need to find a way to create an anchor point to lock your fill in place.

Also not sure, but possibly road bed mat could be helpful. Possibly some railroad ties. Not saying these are the answers just yet, but you need something substantial and yet manageable to hold the fill material.

Rocks mortared together with cement to form a solid and sloped rip rap are another possible option if you can establish an anchor point as a base to keep the rocks from sliding off the mountain. Or just add rip rap rock in series of dumps over time without cement if you can figure out how to keep it from sliding.

Seems like a choice between building a very solid vertical retaining wall w/drainage versus trying to add a lot of rip rap over time to the slope?