Length of flow paths from catchment boundary to river

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10-07-2011 07:30 AM
RonanO_Brien
New Contributor
Hi

I am trying to calculate the length of the path water would take from a catchment boundary to a river within the catchment (basically the shortest path to the river taking the steepest slope each time from each position). I want to calculate this incrementally as I move around the border of the catchment until I have completed a sweep of the catchment boundary. I also want to calculate the difference in height from the start of each path at the catchment boundary to the height of where it joins the river. I have a DEM raster and polygon for the catchment and polyline file for the river already. The DEM was used to calculate the catchment size.

So my output I'd like is all the pathway lengths with their height change all the way around the catchment boundary.

If anyone can help that would be brilliant.

Thanks

Ronan
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7 Replies
DaveGalbraith
New Contributor
No idea, but try converting your catchment polygons to lines, after which these lines will become contiguous sets of gridded points around each catchment.  For simplicity's sake let's think of these gridded boundaries as all having a value of 1, because such a grid could be multiplied with the DEM to produce elevations at the divide(s).  Each catchment outlet is its minimum elevation location (if you already filled sinks), and if in %, the inverse of slope could be seen as the 'cost' to transmit water from the source (watershed boundary) to the destination (outlet).  It may be that you will need to develop a loop that processes each catchment as an independent routine.  That would be a bummer, because loops are kind of a pain.  Good luck, sounds like a cool project.
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ChrisSnyder
Regular Contributor III
Sounds like: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//009z00000053000000.htm

There are a few steps 😉 involved before you can run the Flow Length tool, and if you are new to the ESRI hydrology toolset, take a look here 1st: http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/An_overview_of_the_Hydrology_tools/009...
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ZeraiM__Habtu
New Contributor

I, in fact, encountered the same problem like yours .


I am working on sediment delivery distributed model (SEDD) which i believe , i should  calculate the travel time of the eroded particles along the hydraulic path, from the considered area /cell to the nearest  STREAM REACH as per the definition,.(as shown in the fig )

I used flow-length tool, however it gives a hydraulic path length  down till to the outlet of the basin , Not to the Nearest stream reach .

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BGSWasser
New Contributor II

I was having the same problem and after a lot of tries involving the optional weight raster as input for the Flow Length tool, I found that the only solution is to manipulate the Flow Direction raster such that is has NoData values where the streams are. Using that as the input for the Flow Length tool (and using no weight raster), I now get the desired flow lengths to the nearest stream.

Additionally, as I wanted to determine the longest flow path per subcatchment, I had to extract the flow direction raster for each subcatchment and then use the Flow Length tool on each of those individually. I used a python script to automate the process.

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lassaadkotti
New Contributor

Sir;

Please  i need help; i would like to know the process in arcmap to determinate the time travel (step by step) please 

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ZeraiM__Habtu
New Contributor

Attached is a material from the author and developer of the LS-Tool algorithm

. It may serve a good reference. You may also contact him( hongming.zhang@

wur.nl) , . He is very cooperative

Happy weekend!

On Fri, Oct 12, 2018 at 9:37 PM Zerai Mebrahtu Habtu <zeraimeb@gmail.com>

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by Anonymous User
Not applicable

In the latest versions of ArcGIS Desktop and ArcGIS Pro, we have introduced a new tool in the Spatial Analyst Toolbox, Hydrology toolset that addresses this problem. Please take a look at the help topic Flow Distance—Help | ArcGIS Desktop for ArcMAP and Flow Distance—Help | ArcGIS Desktop for ArcGIS Pro.

This tool takes an 'input stream raster' that can be used as the destination for distance measurements.
You may calculate both vertical and horizontal distance to the stream from any cell within an 'input surface raster'. To compute distance following the steepest downslope path, provide an optional D8 'input flow direction raster' to the tool. This would limit the downslope path along which distance (horizontal/ vertical) is computed, to the D8 flow directions. 

The tool requires an input surface for the entire catchment. However, if you are only interested in assessing the flow distance at catchment boundary cells, you may extract those values from the flow distance tool output using tools in the Extraction toolset An overview of the Extraction toolset—Help | ArcGIS Desktop   

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