Buffer based on elevation

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12-02-2015 06:48 AM
BenjaminMauck
New Contributor

Hi,

I have a wetland shapefile overlying a 2m LIDAR DEM.

I want to create a buffer around this wetland layer that shows the increase in wetland area if the regional groundwater table increased by 1m in elevation. Thus the width of the buffer is dependent on the catchment slope.

The wetland layer has no associated elevation.

Thank you for your help.

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7 Replies
LukeSturtevant
Occasional Contributor III

What type of attribute fields do you have in your polygon layer? How are you analyzing the groundwater table elevation? Do you have a mean slope field for each polygon?

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BenjaminMauck
New Contributor

I am using it has a theoretical exercise and assuming a 1m rise in groundwater levels. The wetland .shp is merely location with some vegetation info. I do not have a slope field for every polygon.

Would it be easier to carry this out as a raster calculation?

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LukeSturtevant
Occasional Contributor III

I may not be fully understanding what you are trying to do, but if you have a DEM you could run it through Slope—Help | ArcGIS for Desktop to get a slope raster. Then run Zonal Statistics as Table—Help | ArcGIS for Desktop using the slope and wetland polygon layer. You could then Join Field—Data Management toolbox | ArcGIS for Desktop with the zonal statistics table to your wetland polygon and then run Buffer—Help | ArcGIS for Desktop based on the mean slope field.

BenjaminMauck
New Contributor

The objective is to identify the new size of the wetlands based in increased groundwater level. So if the groundwater level increase by 1m and the assumption is that all the land surrounding the wetland (up to 1m in elevation above the wetland) will become inundated. So I need a buffer to represent this increase in wetland size based on the current height wetland and the surrounding land of an elevation of 1m that is assumed to be inundated under these conditions. So it is dependent on the elevation relative to the wetland elevation.

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LukeSturtevant
Occasional Contributor III

Do you have a digital elevation model (DEM) that has elevation in meters to work with? If so you could find the current mean elevation of each wetland polygon using the Zonal Statistics as Table—Help | ArcGIS for Desktop . If your wetland polygons are accurate this should give you a decent mean elevation. Then you might consider using the Contour—Help | ArcGIS for Desktop tool to pick out a contour elevation line for each polygon that is the mean elevation plus 1m. The contour lines can be closed to generate a new polygon Feature To Polygon—Data Management toolbox | ArcGIS for Desktop. I would think this would give you a more accurate result because it considers the surrounding topography as opposed to just adding a horizontal buffer on to your existing wetland polygons.

EDITED: I forgot to mention the USGS did a similar study of projected sea level rise impacts on salt marshes. The report is here​. The approached used in the report is similar to what I suggest doing above.

BenjaminMauck
New Contributor

Thanks you fro your help. I will give this a try.

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LukeSturtevant
Occasional Contributor III

Okay. You should try it on a single polygon first to see if that gives you the desired result. If it does and you have a large dataset to work with you could easily automate this task using model builder or python to at least produce a contour line for each polygon. We could help you set it up.

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