Finding Unstable Slopes

Discussion created by KNelsonPL on Dec 4, 2011
Latest reply on Dec 5, 2011 by KNelsonPL

I've been tasked with finding slopes that are considered to not be at rest. Slopes that are considered to not be at rest are ones that have a slope greater then 33 degrees and the subsequent areas above them(See Attached Image.)

What I'm trying to find specifically is the hashed area in the attached Image. The problem is I'm having difficulty figuring out how to do this.

I've already been given what is to be considered the base of the slope based on a slope analysis I ran.


What I've tried so far but am not sure if it makes sense, is to create pts at the vertices of the base slope line. I then assigned it a Z value based off of my 1ft DEM model.

After that I made a copy of the pts off set them 300 ft to the south on the Y-axis(direction the slope is running up hill). I then added 195ft to each pts. Z value.(so it's 33 degrees from pt. to pt.)

I then created a new Terrain which I converted to a DEM  based off of this these pts. This DEM should represent a constant 33 degree slope. I then compared the two by subtracting the Surface DEM from the 33 Degree DEM. Anything with a positive value should be at risk.

The results I got didn't seem right since it was saying the whole area was at risk, which seems impossible since I've visited the site before.

Does anyone know of a better way of doing this? Possibly by running a buffer, I'm not sure how I could create a second DEM for a 33 degree slope after running a buffer though.

Any help would be much appreciated