# Rehabbing a steep fall line trail?



## null11 (Mar 27, 2008)

We need to close a fall line trail (in red) that has a slope of 30-40% and the tread surface and subsoil is a dense clay loam. The trail is situated in a 1-2 foot deep gully that collects a lot of water from surrounding area when it rains. Worse still, the top portion of the trail, while not as steep, channels water into this gully.

We are building a contour trail (in blue) which will zig zag across this fall line trail in three places; two of them on in steeper sections of the gully.

So far my plan is to try to stop the water from flowing down the trail by: placing 8" logs perpendicular to the fall line every ~10 feet and putting in drains on the trail that leads into this gully. I also want to add plants to help retain the soil but don't know if they will survive being transplanted into this dense soil. I am also not sure if the logs will stay put or even be effective at slowing down the water given how steep it is.

What are some methods that have been used to restore a trail like this back to its natural condition?

For the mean time, what can we do to limit the damage to our new trails that cross the gully without putting in bridges/planks? We have tried rock armoring the backslope and creating a rock retaining wall to hold the tread but it was nearly washed out after one rainstorm. We don't have much rock to work with on site and we need to limit the amount of foreign materials used in the trail.


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## Fattirewilly (Dec 10, 2001)

The logs work, the bigger the better, and make sure you need at least 3-4 people to move the logs, that way someone will be less likely to undo your work.

As you bench cut your new trail, stockpile the duff (rooty material on top of the ground) and dirt. Tarps work well for this....Move that dirt and duff to the old trail as part of your reclaiming process. When you're done, there will be no trench.

Transplanting to the old fall line is good, just be sure to bust up the old soil with a pick (mini-x works well for tilling up compacted soil).


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## Walt Dizzy (Aug 18, 2003)

null11 said:


> We need to close a fall line trail (in red) that has a slope of 30-40% and the tread surface and subsoil is a dense clay loam. The trail is situated in a 1-2 foot deep gully that collects a lot of water from surrounding area when it rains. Worse still, the top portion of the trail, while not as steep, channels water into this gully.
> 
> We are building a contour trail (in blue) which will zig zag across this fall line trail in three places; two of them on in steeper sections of the gully.
> 
> ...


My approach would be to divert as much water at the top of the gulley/old trail as possible. At the top, it should be possible to direct the water far enough away that it doesn't just run back in to the gulley farther downhill.

I don't know if it's possible to prevent the rest of the gulley/old trail from collecting water from the remainder of the hillside. I don't know if you are expected to prevent erosion in the park. Was the gulley there before the trail or not?

I'm sympathetic to to the IMBA ideal of sheeting the water off of a hillside, but it isn't practical in all places. In a deep ravine (maybe not what you are faced with?), nothing short of major earth moving with a full size bulldozer is going to change where the water will end up going. Even in a smaller gulley, if enough water is moving through, using log diverts as you are proposing may only end up causing the erosion to move to the ends of the logs.

You need to look at this carefully and make a realistic evaluation of what can be done. It might be better (if the park management will accept it) to allow the gulley to remain, and to run the trail across it in such a way as to

-Prevent water from diverting onto the new trail.
-Impede the water flow as little as possible at the trail crossing. If you armor, place the rocks at the bottom of the drainage channel, and sink them so they are mostly below the surface.

In the park where I work, there are naturally occurring erosion gulleys 20' deep and more into the hillside. I try not to add to the problem, but there are a small number of places where we have abandoned trail that has gone on to from a small ravine. In these places, there is so much water moving through that even if it was practical to prevent the water from flowing down the old trail, the water would quickly erode a new channel right next to it. As you have discovered, keeping the trail off the fall line is even more important in a water flowage area than elsewhere.

Not trying to talk you out of being a responsible custodian of the land, but do be realistic in picking your battles. Some areas with high water flow are going to erode a ravine no matter what anyone does. If someone before you built a trail in the bottom of a ravine, it's not going to make the ravine go away to move the trail out of it. Other areas with more reasonable flow can be managed. Have you been out there in the spring rains to see what's happening?

Good luck and thanks for your efforts.

Walt


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## null11 (Mar 27, 2008)

Thanks for the advise Walt. The main goal is to prevent damage to the new trails, but it would be nice to keep the hillside from washing away. I can't tell if trail traffic has formed the channel that is causing the problem or if it is the natural lay of the land. It is probably a combination of both. The rains we have been having lately are negatively affecting the trail for sure.

Today we added four log check dams into the gully right before we were hit with a 4/10ths inch of rain in a span of an hour. I went back out an hour after the rain had stopped and the water had washed away the soil we placed upstream of the log dams in the steeper sections of the gully and even cut a path under one of the logs. Our technique may need some refinement as we didn't use very large logs. Would putting some type of rock aggregate behind the logs would work better than soil alone?

I have attached some photos of the area with the work we have currently done after todays rain.

1st photo: Rock armoring at the new trail crossing the gully in the steepest lowermost section. It could use some improvement.
2nd: Looking uphill from below the lower trail crossing.
3rd: Crossing at the top of the gully with the previous trail leading to the right. Three check dams are visible; the top two were added today.

Another concern is users still using the gullied trail because it is the most direct route to the previous trail. We have placed quite a bit of dead fall into the trail and people have still been using it. I would like to get plants growing to conceal the old trail, but the effects of breaking up the soil to do so may be quite bad or the plants may be washed out by our seemingly frequent heavy rains.

I will keep in mind that it may be a loosing battle trying to fix the problem, but I don't think I am ready to throw in the towel yet. Rain is in the forecast for tomorrow (~0.75 in) so I will see what happens after that.


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## HarryCallahan (Nov 2, 2004)

I think people are going to keep taking the old line unless you bury it pretty deep with brush and logs. Run-off is going to keep coming down the middle of it unless you can fill in that trough.


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## Walt Dizzy (Aug 18, 2003)

null11 said:


> Thanks for the advise Walt. The main goal is to prevent damage to the new trails, but it would be nice to keep the hillside from washing away. I can't tell if trail traffic has formed the channel that is causing the problem or if it is the natural lay of the land. It is probably a combination of both. The rains we have been having lately are negatively affecting the trail for sure.
> 
> Today we added four log check dams into the gully right before we were hit with a 4/10ths inch of rain in a span of an hour. I went back out an hour after the rain had stopped and the water had washed away the soil we placed upstream of the log dams in the steeper sections of the gully and even cut a path under one of the logs. Our technique may need some refinement as we didn't use very large logs. Would putting some type of rock aggregate behind the logs would work better than soil alone?
> 
> ...


Thanks for the additional explanation and photos Null11. The situation is much clearer now.

I support your desire to improve a bad situation regardless of what originally caused it.

Again, the best bang-for-the-buck (of labor that is!) is to divert the water at the top of the hill. From the appearance of the log diverts on the hillside itself, the reason they aren't working is that they aren't big enough. In other words, to make the water divert out of the ravine, it isn't enough to sink logs across the channel. The diverts have to be higher than the outside edge of the entire area that is affected. If you are determined to make this work, my $0.02 is to pick one or two places on the hillside and use a combination of logs + dirt + digging a diversion channel across the outer lip of the gulley to be sure the water has a way to get out of the gulley.

Also, if you cut/build up the diversion channels at an angle down the hillside instead of at right angles across the gulley, it will reduce the amount of dirt you have to move and be less prone to washing out. What you are aiming for is something like a rolling grade dip if that helps you to visualize the structure. Edit/ Make sure your new divert doesn't end up dumping the water onto your new trail! /Edit.

It's far more effective to have one or two diverts that work than to have lots of small structures that get overwhelmed.

The issue with keeping riders off of the old trail in my experience is you have to add enough debris to make it disappear or at least look unrideable for 30-50 yards or so. There was another thread on this same problem recently, do a search on this forum and you will find that one thread and more. My $0.02 is if you lay lots of large sticks and branches in the old trail parallel to the direction of travel (not perpendicular), as far as the eye can see from the point where the new trail begins, that will discourage people from riding it. As an added benefit, the branches will collect leaves and other debris as time goes on and reduce erosion on the old trail.

Best wishes for your success,
Walt


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## gmcttr (Oct 7, 2006)

In addition, the rocks you have used are way too small. This amount of water flow would require larger flat rocks deeply embedded on edge to stand a chance.

I would suggest using small wood bridges and let the water flow under them if you are not successful at diverting it.


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## fully (Sep 14, 2004)

*bigger check dams!*

+1 for breaking up existing fall line... we've found a garden tiller makes fast work of this task.

Also, the check dams we've built on similar reroutes are each made from at least a half dozen logs buried on the ends and tied together -- a serious blockade for water/silt every 10' or so... These are almost 2' tall on the downhill side. Over time, the uphill side silts in and stuff grows on top of the sediment.

So, you're demonstrating the principles, but need to go bigger with all of your materials and treatments :thumbsup:


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## null11 (Mar 27, 2008)

Fully, great idea for the check dams! I don't have access to or the means to move large rocks, but there are plenty of freshly fallen trees. I never thought about standing logs on end for the check dams. I will try this out and see what happens. Can you elaborate a little more on the process of tying the logs together?

Last night we received about an inch of rain and nothing had changed as far as I could tell on the trail.

Today I dug a drainage channel (Photo 1: blue dots) to divert the water being fed into the gully from the above trail. I also blocked the existing fall line (Photo 1: red dots) with much more dead fall and debris and transplanted a few shrubs into the existing trail. I tried a larger check dam with 12" diam. logs (photo 2 & 3). More rain is forecast for today so I will see how it works by tomorrow.

Much thanks for all the advise.


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## fully (Sep 14, 2004)

*Not end to end...*

Wider and taller. Lay logs perpendicular to the trail (as you have so far), but use longer/more logs to cover the width of your drainage and stack more logs on top. You can wire to keep them in place if you like. Take the dirt you excavate to bury the first row and pack it to the uphill side. This technique has 'disappeared' several segments for us. It will take a couple of years really fill in with plant material.


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## bweide (Dec 27, 2004)

It helps if you use logs significantly longer than the width of the gully and then dig the ends deep into the sides of the gully. The bigger the logs the better. On a fall line trail diverting the water out of the gully really doesn't help because the water flows down the hill immediately parallel to its old channel and it usually manages to flow back in.


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## Trail Ninja (Sep 25, 2008)

Looks like the drainage channel will work. 

In case it doesn't, what I would have done is let the water run in the original channel, even dig it out a bit to encourage it. It would narrow your wet area and eventually erode it quite deep. Put BIG rocks in the water channel to make it unrideable and bridge the channel where the trail crosses it. 

It's really tough to argue with water. I usually try to figure out where it wants to go and help it along.


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## Boulder Pilot (Jan 23, 2004)

It's a little hard to tell from the photos, but it looks like those are just water bars, which, in time, will cause more erosion. As stated previously, you need to minimize the volume of runoff at the top from entering the channel. I don't know how much rain you get, but your "drainage channel" looks to be pretty shallow and narrow. A little debris will clog the channel up, overflow, and widen the existing area you are trying to fill in.

If you don't build check dams up to the top of the channel, and continue this downslope, you will not accomplish what you mean to accomplish. As far as your new trail, you might consider grade dips with heavy armoring where the old crosses the new.

And trail ninja makes a good point. If you are not saving this old trail segment and it is acting as a drainage channel, it makes no sense to me to build another channel right next to it.

Remember, I'm basing this my interpretation of the photos.


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