# How to create a surface with a slope of 2%?

I am working on a project where I have a polygon of a basin that I should create his base whose elevation begins at -1m and go down in every direction with a slope of 2%. Does anyone know how to do it automatically using ArcGIS?

• By surface you mean Digital Elevation Model (DEM) raster? – BERA Jun 28 '18 at 13:38
• No exactally. I want first to create a polygone or polyline limiting the base with a Z-value and convert it later int a TIN then in a raster. In the final step I aim to calculate the volume between the zero surface and base using Cut and Fill tool. – El Mahfoud Jun 28 '18 at 14:18

## 1 Answer

You can compute the distance to your reference point (Euclidian distance tool), then you divide this distance by -50 and substrat 1 to the results in the raster calculator (map algebra tool).

Some explanations: the slope percentage is equal, by definition, to the maximum difference in elevation divided by the planimetric Euclidian distance. The Euclidian distance tool creates a surface with values of the planimetric distance. If you assume that the generated result (distance in the X/Y plane) is in fact an elevation value, then this would represent a DEM with a positive slope of 100%. Now if you divide the "synthetic" DEM values by -50, it becomes a DEM with a slope of -2% and an elevation of 0 at the location of your reference point. then you can remove 1 m from the all DEM, which will not modify the slope but set the elevation of the origin at -1 meter.

• Thank you, but May be I should explain more. The area of the base is still unkown because it depends on two thing to be respected: 1) the slope between the ridge of the basin and the base is about 66.67% (3H2V concept). 2) The base surface slope is decreasing by 2% from a reference point having Z=-1m – El Mahfoud Jun 28 '18 at 14:47
• well, it is still unclear to me HOW you decide of the boundaries of your base, but I have edited my answer to better describe how the DEM generation works. I suggest thatyou ask a second question if you don't know the boundaries of your base – radouxju Jun 29 '18 at 6:49
• Thank you for your efforts. In fact, yes, I have no idea how to define the boundaries of the base, so I should repost my question with more details as you propose. – El Mahfoud Jul 2 '18 at 8:20