Because it is straight down the "fall line"--directly down hill, the route water takes when flowing over the ground--and due to use (it's the lowest spot along the slope) this short segment collects a fair amount of water and allows it to run quickly. The combination of volume and speed of water is a guarantee of erosion, creating a nice little gully, that of course hikers want to avoid, which means they walk along side of it, widening the trail and creating another site for more erosion.
The best way to address this issue, is not to let it happen in the first place. Trails should cross slopes at an angle climbing/descending more gently. Ideally, 12% is the maximum desired grade for foot trails to prevent water from getting up enough speed to start washing material off the trail. For some perspective, an interstate highway specification is for no more than a 7% grade. Another way to think of grade is the amount of "up" you need to cover in a given distance of horizontal travel. 12% is about 1" of up in 8" of travel. A 20 foot section of trail at 12% would have a rise of about 28 inches. This is noticeably steep for a hiker, but hikers and trail managers in New England consider this kind of slope a luxury. Through tradition, or because of limited available land or geology, or just Yankee stubbornness, a 12% trail is pretty rare around here.
So, you have a steep trail and it is subject to erosion, what can you do? First off is to find ways to get the water off of the trail at frequent intervals so it doesn't build up speed. Waterbars are the most often used means--channels cut accross the trail, strengthened by rock or timbers--that sluice the water sideways off the treadway and into the woods. Unless they get clogged with leaves, dirt, or rocks. Or the rocks that strengthen them are not large enough or set poorly. Or hikers walk around the ends pounding down the dirt and providing a new route for water to continue down the trail. As a Maintainer, you can address the first of these shortcomings. As a Trail Builder, you can address the second. The third? Well, that's up to Hikers. There are vastly more of them than there are of the other two groups. Just suck it up and go straight over the water bars--don't walk around them...
So, I've got that off my chest, let's talk about rock steps. When you have no choice but to go stratight down (or up) and the slope is steep, steps are the only answer--and one of last resort. Steps take a long time to build. If you want them to last, build from rock--it never rots. But, you need to have a source of rock that is suitably sized (big), shaped (has at least one flat side, preferrably two or more) and close to the work site. You need to be able to set this rock deep into the soil and against other rocks so they will never move again. This takes time and some skills that are best imparted by working with an experienced crew leader. Surprisingly, you don't need to be a body builder to work with rock--even big ones. Learning how to use simple tools and (occasionally, but rarely) a modest amount of basic rigging, regular people can move really heavy things pretty much right where they are needed--very slowly. There is a level of craftwork that needs to be done, but you learn it by doing it. The work is hard but honest, in the sense that you are dealing with elemental materials and forces. The satisfaction is high, there's something to look at after a hard day (or days) in the woods. This thing you have helped to create has an immediate practical value--and if built right, you can show it to your grandchildren.
OK, on with the project. We had 8 of us at the trail head on Tuesday morning. A large crew by our standards--and most welcome. A short hike on a humid morning brought us to the shelter and project site.
We gathered around the blown out section and discussed our options--either by installing new steps directly into the existing gully, or creating the steps on an undisturbed slope immediately adjacent. Keeping the trail's footprint small by staying in the gully had some appeal, but the exposed bedrock and likelyhood of continuing water problems favored starting fresh, and we were also able to take advantage of a slightly more favorable slope.
|Mining crew at work while Don clears a downed trees|
For this project, the rock "mining" was pretty simple. Just up hill was an even steeper slope/cliff, that had produced what looked like a lot of reasonably sized and shaped pieces that would be easy to transport to their new home.
|Some rocks are easier to get to than others.|
Once pried out of the hillside where they had been sitting since the glacier left, the next step is to get the rocks down to where they would be set to create a step. Given the small work site, we did not want to just send boulders down the hill willy-nilly. Being a bowling pin is not a good thing.
|Anita and Jim coax a rock down the hill|
To create the most stable stair, each rock should rest on its neighbors below (and in some cases to the sides). Putting the front edge of the next step onto the back edge of the step below works with gravity to keep everything together. Simply excavating holes in the soil and dropping rocks in usually results in the rocks creeping downwards or being squeezed out of their position by frost and/or water flow.
Once the bottom rock is set, the slope behind it is excavated to receive the back of the next step. The art of this process is gauging the size and profile of the excavation to match the incoming rock, and finding the best way to mate the surfaces where the rocks contact each other.
|Step number two is landed by Silvia, Dave and Jim.|
|Don, Jim and Denis coax step number three into place.|
|Day 1 has 8 steps in place. 4-6 more to go.|
To help keep hikers on "the straight and narrow", the sides of the stairs are lined with vertical slabs and the earth on either side of the steps will be covered with "scree" rocks--loosely piled rocks that deter hikers from walking alongside the stairs, increasing the opportunity for more erosion.
|Denis and Don install the last few steps|
|The scree rock is stacked alongside the stairs to reduce walk around.|