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Buffer a stream network polyline at specific distances upstream from study site

Question asked by davisem on Jul 14, 2014

Hi all,

 

Hoping someone can help with this problem.

 

What I'm currently attempting to do is to create riparian buffer zones around different lengths of stream (so I can analyze how fire in the riparian area affects stream variables at different scales).  I've already created 20-m riparian buffers that span the entire catchments of the streams I'm interested in and extracted the fire severity values for the buffer zones in those catchments (the colored rasters you see on some of the catchments). Now I aim to scale down to buffers at 0.5, 1, 1.5, 2, 2.5, 3, 3.5 and 4 km upstream of my study points.  I want to do this because it's likely that conditions in the riparian zone only affect stream variables up to a certain distance away from the study site, but I'm not sure what the limit to upstream influence is. 

 

I already know how to create multi-ring buffers from a certain point, but those only use Euclidean distance from the survey site and don't take into account the curving of the stream. I want to measure the distance using the stream polyline itself.  Here's what I've done so far:

 

1) I took the  stream network polyline for my AOI (reach_lmfs) and dissolved all the reaches into one feature (so it wouldn't be composed of thousands and thousands of features, each its own line feature). 

2) Using this new polyline (NetworkDissolve), I tried to use the Split Line at Points tool.  The points I was attempting to split at were the study site points (sitePoints).  My aim here was to get separate feature classes consisting of unbroken lines starting at the sitePoints and including everything upstream. 

3) Oddly, the tool did not do this.  Instead, it broke the NetworkDissolve layer back up into its original component reaches (I have no idea how!).  This layer is called Take3Split.

 

If the tool had worked, my next idea was to use the Split command on the Editor drop down menu to split at a certain distance upstream from the site points (measured directly on the stream lines) and using those split lines of the specified distances upstream from the points, create new points, measure what the diameter of the circular buffer should be, and then make the buffers using those distances.

 

Any advice/ideas? Maybe I am going about this the wrong way and should be using linear referencing instead? Or network analysis? Neither of which I know anything about, of course. here's a link to a map package on Google Drive which has all my layers and necessary data so you can see what I'm talking about.  https://drive.google.com/file/d/0BxKVn0O6wccZaEplWEFxcHE4blU/edit?usp=sharing

 

Thanks!

Emily

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