I have used short star pickets driven into the ground and have placed treated timber planks against the and back filled with stones, carried up or down each trip.
The posts are set so that the top of the boards line up roughly with the bottom of the step further up the hill.
It does pay to have the posts set below the top of the wooden board so you are less likely to kick them.
Posts are about 18 inches apart and the timber is 6 inches wide or narrower if the slope is less.
Minimal disruption to the surrounding area, and mine are 30 years old.
John Daley Bendigo, Australia
The Enemy of progress is the hope of a perfect plan
Very interesting and useful guide... but it specifically does not include any information about steps aside from a directive not to use them on Park Service trails unless unavoidable.
One of the last pages, covering waterbars for diverting water from hillside trails, may be applicable.
In the OP's case, depending on the character of the riverbank I would probably use sections of log with stakes driven into the bank to hold them.
Is the bank subject to erosion, or does it stay where it is even in floods? How soft is the soil, and how stony?
My procedure in general would be to cut stakes from durable wood (black locust, cedar, redwood, or whatever is available in your area). Stripping the bark will retard rotting somewhat. I would use 2 to 3" stakes, or larger split in half, about 18" to 2' long (more in deep soft soil or very steep slopes). Starting the stake holes with a digging bar will make the job much easier, and if the soil is stony, may be the only way to drive stakes deep enough for stability. I like to drive the bar fully as deep as I intend to set the stake.
Then excavating a bit behind the stakes so the log nestles into the ground will make it more stable. Either make the step wide enough that the stakes on each side are not in the way of foot travel, or cut the stake tops off flush with the top of the step log. You may want to flatten the top of the step log if it is larger than 6" or so.
Where the terrain and resources are suitable, my favorite method is to set flat stones into the hillside, with appropriate bracing for stability. This is an advanced technique and can be dangerous if done by someone not experienced in dry stone masonry.
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