topic Re: 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? in Mapping Questions

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 — Mon, 19 Oct 2015 14:55:44 GMT

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.

Re: 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?

ChrisDonohue__GISP — Mon, 19 Oct 2015 15:09:20 GMT

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

Re: 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?

DanPatterson_Retired — Mon, 19 Oct 2015 15:09:45 GMT

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.

Re: 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?

WesMiller — Mon, 19 Oct 2015 16:04:00 GMT

It may not be the solution your looking for but you could select the contours that intersect your buffers convert your buffers to lines Feature To Line—Help | ArcGIS for Desktop then merge the buffer lines and selected contours Merge—Help | ArcGIS for Desktop then convert the new feature class back to a polygon Feature To Polygon—Help | ArcGIS for Desktop then the only challenge is removing the polys that you don't need.

Re: 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?

DarrenWiens2 — Mon, 19 Oct 2015 16:37:07 GMT

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.

Re: 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 — Mon, 19 Oct 2015 16:45:26 GMT

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

Re: 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?

DanPatterson_Retired — Mon, 19 Oct 2015 16:55:07 GMT

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.

Re: 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?

NeilAyres — Mon, 19 Oct 2015 17:21:04 GMT

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....

Re: 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 — Mon, 19 Oct 2015 17:50:21 GMT

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

Re: 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?

ChrisDonohue__GISP — Mon, 19 Oct 2015 18:59:07 GMT

Ouch. This sounds like a thorny policy issue. As Dan Patterson pointed out, the Buffer is an abstraction to begin with, with the general idea being that activities within its extent are a likely risk to a water feature. But in your case it could be argued in the real-world that a facility upslope of the buffer (even a 3D one) but just outside it would be a risk too, as a steep slope may make it more conducive for a spill to reach the water. And conversely a facility inside the buffer but downslope from the water feature may not be a risk to the water feature. So some potential "exceptions".

In the Environmental policy world, using a normal buffer (not 3D) is typically done as pragmatic trade-off in trying to protect a resource in a standardized way. It is a "one size fits all" approach that tries to achieve protection by balancing the cost of analysis for a multitude of varied sites with the Administrative realities of doing so, realizing that it is not perfect for each site.

For example, here in California the State mandates a specific distance buffer (2D) around Vernal Pool features, as they are considered by the State to be Sensitive Habitat and typically contain several endangered species. It is a set distance for all cases, with no variation for the topography. However, the State does provide a process where one can file for an exemption by proving that the planned activity that would fall within the buffer is actually downslope from the pool's watershed, and therefore a spill would not affect it.

So I guess it will depend on how the policymakers have developed the existing policy and how they will proceed with the new one.

Chris Donohue, GISP

Re: 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?

DanPatterson_Retired — Mon, 19 Oct 2015 19:20:02 GMT

So in essense they want their buffer...

Consider the following:

proposition 1 ... a 3D buffer distance will will be used to delineate the greatest distance in the horizontal plane
abstraction
- a buffer restriction of 100 feet exists in legislation saying nothing can be built within that buffer zone
- a cliff of 90 feet exists in the landscape within 11 feet of the river at some point along the rivers course
conclusion
- structures can be built to the edge of the cliff and 1 foot down its surface
proposition 2 ... a 2D buffer distance will will be used to delineate the greatest distance in the horizontal plane
abstraction
- same buffer restriction as above
- the distance along the cliff face (ie the vertical distance) is not in the calculation of the horizontal offset
conclusion
- structures cannot be built within the delineated 100 foot offset in the horizontal plane
summary
- they want the cliff proposal
- everyone else wants Euclid's proposition

A bizzare, but not improbable abstraction given the wide variation in near river cliff heights and legislative offsets that exist in parts of the world.

This is not a fun situation, but when push comes to shove, Euclid always wins

Re: 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 — Mon, 19 Oct 2015 19:27:19 GMT

Correct this is an option, but I don't think it's feasible in terms of replication and consistency (also probably not efficient)

Re: 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 — Mon, 19 Oct 2015 19:28:22 GMT

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

Re: 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?

DanPatterson_Retired — Mon, 19 Oct 2015 19:32:12 GMT

So in essence a "flood" where at the "pour point" they want a certain horizontal offset which would diminish upstream .... (with the consequence of increasing downstream .... but we will just ignore that tidbit until someone notices it 🙂 )

Re: 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 — Mon, 19 Oct 2015 19:35:44 GMT

Thank you for the response and insight, I think what might happen is that the companies filing a lawsuit (or appeal) will be able to argue their case and if they win then I will have to revise that particular zone. Which, to me doesn't make sense because that will set a precedent for these companies to file for an appeal when ever they don't want to pay out of pocket.

Re: 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?

ChrisDonohue__GISP — Mon, 19 Oct 2015 19:51:19 GMT

Sorry, we are wandering off topic from what you need, which is a way to do the 3D Buffer in GIS, as that may become a requirement. The backstory is always good to know.

If you haven't already checked, I'd go with Dan Patterson suggestion of checking out the code written by Xander Bakker.

Creating a surface buffer?

This may accomplish what you need. The code was written to do a single point and buffer it in 3D. If the extent you need to buffer is not a single point, you could post the type (line, polygon) here and I suspect the many skilled Python guru's on GeoNet would likely come up with a solution.

Chris Donohue, GISP

Re: 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?

XanderBakker — Tue, 20 Oct 2015 12:42:27 GMT

A thing to keep in mind when doing a Cost Distance using the slope is that the system will not consider the slope in the direction of travel. It is just a value indicating the maximum slope.

Let's say that the (maximum) slope in this case is somewhere around 45°, buy in the direction of travel (red arrow) the slope is 0°. That is why I created the script Creating a surface buffer? mentioned by Chris Donohue, GISP . It think the whole issue is not simply solvable considering just (surface) distance, but a lot more complex.

Re: 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?

DanPatterson_Retired — Tue, 20 Oct 2015 13:47:06 GMT

which is why I suggested pathdistance way back up at the top of this thread as another option to your implementation. There are some examples of the factors you can simulate

What may gained by minimizing horizontal travel in one direction will be lost if the same principles are applied in various directions of travel

Re: 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?

JeffMatson — Tue, 20 Oct 2015 15:10:30 GMT

Sorry if I'm missing something obvious in your requirments - but why not just 3D buffer the stream, then intersect that result with a surface model to generate an "effective buffer"?

Re: 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 — Tue, 20 Oct 2015 15:59:52 GMT

Hi Jeff,

I would appreciate it if you could elaborate further on intersecting the 3d buffer with a surface model.The main requirements (parameters):

1000 ft buffer on main stem "main portion of water" form the left and right banks
500 ft buffer on all tributaries
500 ft buffers on all intersecting water-bodies (ponds, reservoirs)
1000 ft buffer on lakes
potential parameter requirement
- account for topography in buffer

There are other parameters concerning the stream's time of travel to the nearest surface water intake, but these aren't in question.