Is it possible to take pre-existing buffers, make them "flexible", and overlay those buffers onto a topo map, so that the buffer would reflect the contours?

[ShannonShy]

     Some background, so I work for and go to school at West Virginia University and I have been subcontracted to work with the DEP on stream management and analysis for the entire state. My most recent project has been to create buffers around streams leading to surface water intakes in order to help monitor chemical spills and also regulate tanks used by oil and gas companies.

     My problem is that when creating the buffers around the streams I failed to include elevation and slope when calculating the distance of the buffers from the stream center (left and right banks for major rivers). My idea is to take the buffers I have (~160 of them) and make them flexible to reflect the topography because 1000 ft linearly looks a lot different than when that same 1000 ft would "decay" because of the topography and slope. I imagine my buffers being able to snap to contour lines to limit the planar length and reflect the topography.

     I'm also wondering if using any tools in the 3D analyst would be of use, tools such as 3D length...I'm just not sure.

     I'm aware that this could be solved by re delineating these buffers by working out of grid and also using cost-path but I would like to save myself the trouble of having to do these again since the entire project took about 6 months due to tedious calculations and attributions.

Thanks!

I am using Arc Map 10.3 and surrounding software.

[ChrisDonohue__GISP]

It may be possible to just re-run the buffers using this tool.  However, I have not used this tool myself, so am not totally sure.

Buffer 3D (3D Analyst)

ArcGIS Help (10.2, 10.2.1, and 10.2.2)

Someone who probably knows is:

Darren Wiens

(added in case he has ideas)

Chris Donohue, GISP

[DanPatterson_Retired]

Xander Bakker​ produced a working script for a point, but not a stream in this link.​.  In any event, should you have to go the raster route, it would be  path distance​ not cost distance should you wish to account for horizontal and/or vertical cost factors.

[DarrenWiens2]

Just echoing Dan Patterson​'s suggestion for using Path Distance, with a couple extra notes.

- I believe you actually could use Cost Distance, if you really wanted, by calculating the cost from the stream layer over a slope raster (not DEM), scaled by cell size. High slope = high distance/cell = high cost. But, Path Distance already does this for you.

- You can't use 3d Buffer. This will produce a cylinder around your stream, but not take into account the topography between the stream and your buffer distance.

- You can't use contour geometry directly whatsoever, as the desired distance should almost never follow a contour line. Your stream is going downhill, and so should your buffers (generally).

- Regarding using your pre-existing buffers, I think this would be possible, though complicated to implement, using 3d graphics software like Blender​ (you can import DEMs and shapefiles), but AFAIK not ArcGIS. Before you go down this rabbithole, Blender does choke up using even moderately large elevation datasets - I wouldn't recommend this route unless you're really interested in learning the software.

[ShannonShy]

I agree that Cost Distance and Path Distance might be my best option. The challenge is replicating this process for ~160 zones, all of which have unique topographic features that surround the streams. Also being able to adopt this method for future delineations of new zones

[DanPatterson_Retired]

I would pull out a few from the extremes of the spectrum and do a quick study.  I think that you may be ... pardon me ... overthinking or worrying about this too much.  Remember the buffer itself is an artificial constraint and any work that you put into precisely delineating such a feature in space would be wasted time.  You might better take that time and find your worst case scenario, a typical case and a no problem (aka flat) area and do a demo and show that in the steeply sloping areas the position of the buffer will be different by XYZ amount you can steal this...

      " In those areas of steep slope, it may be prudent to employ a slightly larger buffer to accommodate the affect of slope on the buffer delineation.  One should remember that the buffer itself is a conceptual delineation and not a physical barrier"

or words to that effect.  I have found in my experience that doing the case study is generally enough to satisfy those in the decision process.

PS  Addendum

If this specific issue is not in the original contract, then you also don't have to include it and/or point it out.  But by indicating that you have thought about it, then you may get the kudos-high-five and perhaps some more funding if deemed critical to moving forward.

[NeilAyres]

It seems to me that this buffer(?) is similar to producing some sort of elevation isoline above the stream. ie make "contours 1m above the streamline". These are not elevation contours because, as Darren says, the stream is always going downhill. Been fiddling with this a bit, but havn't got any coherent code for this yet. But if anyone has found something which does something similar, then please share a link.

Sorry for hi-jacking this thread....

[ShannonShy]

No need for apologies because I'll be taking the code if it is produced!

[TomLee2]

Neil - I do something similiar that might help you, although it's not exactly what you're looking for.

I sometimes use gauge readings to model stream heights. A gauge is a point, and has an attribute for the elevation of the stream. I take the points shapefile, use IDW to create a surface of the stream height, and then I get a raster of the interpolated stream height over an area. Then I subtract the ground elevation DEM from the interpolated stream height DEM - they're both rasters so I use the raster calculator or the 'minus' tool [raster calculator needs spatial analyst, 'minus' tool needs 3D analyst]. The result is a raster of stream depth.

So, what you could do, is create a point file of your stream boundary lines, then get elevation attribution for the points from a ground elevation DEM, then add 1ft to the stream points elevation attribute, then IDW to create a raster surface of the increased stream elevation, then subtract the ground elevation DEM raster from the increased stream elevation raster, with the result being an approximate stream depth with 1m added.

There's a little bit of cleanup needed to get the boundary as a vector line. Reclass the raster to two classes of stream and non-stream, then convert to a vector polygon file, then remove all the polygons not attached to the stream, then display your stream polygon as a boundary line or convert it to a line.

There are many different ways to do this problem. You also could have taken the stream elevation raster and created contours from that. Or you could do this with TINs instead of rasters.

Just think of this problem as you want to make the stream go up, so you need the stream to be a 3D feature. You need to work on the stream, not your ground elevation contours.

[ShannonShy]

Well to be short, the oil and gas companies are not happy with my model (it is a revised model compared to the old standard) and my new model will cause them to register more tanks which results in less money for them. All in all there is a lawsuit (not against me personally) to say that the zones would need to reflect the topography.

So it may be court ordered that the zones be revised