Weighted Flow Accumulation Processing Time

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09-24-2013 08:36 AM
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NickLegg
New Contributor
Hello ArcHydro Users,

I am attempting to run a weighted flow accumulation, and am having issues with excessively long processing times. My input flow direction raster is approximately 8000 cells by 8000 cells (with an irregular shape).

As a trial, I ran the flow accumulation function on the same flow direction raster, but without a weighting raster. The processing time was approximately 2.5 minutes.

When I run the flow accumulation with a weighting raster, the processing time is at least 12 hours (and still running). I've attempted this operation multiple times, and have not yet had it finish successfully. My weighting raster is composed of integer values of zero and one, is the same projection as the input flow direction raster (Washington State Plane), has the same cell-size (30 meters, or 98.425 feet)  as the input flow direction raster, and is snapped to the grid of the input flow direction raster. Because the weighting raster is much larger spatially than the flow direction data-set, I also limited the processing extent using a mask of the input flow direction raster (under environments).

While I don't know the exact nuts and bolts of the flow accumulation algorithm, my feeling is that the weighting raster shouldn't result in such an increase in processing time (from minutes to days). I also ran some weighted flow accumulations on other test (smaller rasters), and had minor to non-existent processing time increases over the standard (un-wieghted) flow accumulation. Has anyone run into similar issues? Where am I going wrong?

Thanks for your insights,
Nick
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MarkBoucher
Occasional Contributor III
If you are working with your source data and results data on a server, your calculation times will be long and mistery errors can occur. When I put the data on my local local PC, I am amazed at how fast and error free the spatial analyst calculations can be.

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AndrewMoffitt
Occasional Contributor III
Hey Nick,

Very detailed writeup, so kudos for that.

Without doing much work, how hard would it be for you to clip (extract) your weighted raster to the same extent or boundary as your flow direction raster?  There might be a bug that makes the tool not honor the extent.
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NickLegg
New Contributor
Thanks, Andrew. I had tried clipping the weighting raster as well, and had similar issues.

The plot thickens: On a few of my attempts, I cancelled the operation. In most cases, my cancellation resulted in an ArcMap crash (further fueling my frustration!). However, on two occasions, the cancellation actually finished, and then output the weighted flow accumulation. The output raster in these cases were the full project extent with correct values (i.e. exactly the output I was hoping for). This all tells me that the flow accumulation operation is somehow stalling out, and continuing to run unnecessarily. Unfortunately, this whole process of having to cancel to get the right output is extremely inefficient, especially considering that I have to run the operation 50 or so times (and was hoping to batch process or iterate in Model Builder).  

Has anyone experienced similar issues, or have any possible solutions about my problem. My next solution is to try running this on another computer with a different version of ArcMap.

Thanks for any help in advance.
Nick
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MarkBoucher
Occasional Contributor III
If you are working with your source data and results data on a server, your calculation times will be long and mistery errors can occur. When I put the data on my local local PC, I am amazed at how fast and error free the spatial analyst calculations can be.
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NickLegg
New Contributor
Thanks Mark. Just before your post, I broke down and ran the operation on a desktop version with the files stored on a hard drive, and had no issues what-so-ever. I had all the issues working on a remote desktop version of Arc, with both input and output files on servers.

Best,
Nick
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