Topography Slope Rise and Run Limits

Discussion created by jsimpson@apexcos.com on Feb 5, 2018
Latest reply on Feb 5, 2018 by Dan_Patterson

I am running to a calculation problem that is totally racking my brain. I will try to explain to best that I can. What I have is raster dataset with elevation data for site (topography raster). What I am needing to do is identify areas that are less than 5% slope, between 5% and 12%, and 12% or greater. The compliance document I am following prescribes that development cannot occur on slopes greater than 12%, and special permit is required for slopes between 5% and 12%, so I need to call these out separately, and basically ignore the slopes less than 5%. However, there is a stipulation in the document that the slope requirements only applies when the slopes exist for a run of over 50 feet or if the rise is over 6 feet. This is where I am getting lost. What I have done so far is run the raster slope tool on my topography raster, resampled the raster to convert the slopes to integers, run Raster to Polygons, then dissolved based on the integer slope value, lastly symbolized the polygons into three classes for the 3 slope intervals listed above. So my end results is a polygon feature class with three areas of slope classification (see attached, blue is <5%, green 5-12%, orange >12%). Most of the areas from manually measuring do not meet the rise/run stipulation listed above, and aside from manually going through this and measuring and deleting stuff, I am at a loss of how to apply these requirements to the data. Does anyone have any ideas on methodology of how to apply these two requirements to that data and export a polygon feature class of slopes that only contains what I need? If i can provide any additional information or data that could help, please let me know. Thanks!