Flow accumulation taking forever. What am I missing?

[RachelDiPietro]

Hello,

I have to do four topo maps for an assignment in a GIS class (asked professor first, she said looking for help on forums was acceptable), and currently the only thing that is holding me back from finishing them is the flow accumulation. I am using ArcMap 10.3, I believe.

I did everything in the right order with no problems: Project Raster, Fill DEM, Extract, Hillshade, and Flow Direction. However, whenever I try to do Flow Accumulation, it just keeps going with no sign of stopping. I fill in all the fields properly, with the Flow Direction raster as the Input, save an Output raster in my geodatabase, and set the data type to Float. My most recent time trying Flow Accumulation, it went for twenty minutes straight before I decided to cancel it. (This is working with the extracted part, so the area it needs to cover is much smaller and shouldn't be taking long to finish.)

Whenever I cancel Flow Accumulation, exit and reopen ArcGIS, there is still a Flow Accumulation raster present in my geodatabase, and when I add it to the map, it is always complete except for one small cell in a random location where you can still see through to Flow Direction. Sometimes I get a message saying Serious Error rather than ArcGIS, and I just send a blank note to bypass it.

I am pretty new to GIS, and I did not have this problem the last time I used it for a step by step lab instruction. Am I just being impatient, or is there something I'm missing here? The assignment is due next Friday, and I am concerned that I can't get it done on time because of this problem. Has anyone else encountered this issue, and if so how was it resolved?

Update: I tried flow accumulation in a different map file for this assignment, and after about a minute it just gives me three different errors: generic error with no identity, error encountered while trying to read the specified grid, and error while reading the algabraic function. I do not know if this is the same reason the flow accumulation just keeps running in the first map, but I am really at a loss as to why I can't use flow accumulation properly.

Any help would be greatly appreciated!!

[DanPatterson_Retired]

The important information is needed

1. is this an esri grid? a tiff? or what
2. what is the cell size?
3. what is the extent?
4. given 1 and 2 is this file really big.
5. since you casually mentioned that there were 4 inputs, are you sure that there is no band of nodata cells where the rasters were placed together... that would make pretty anything stop AND probably wouldn't get filled when you did the sink
6. assuming that 5 is ok and you have used fill sinks, then checked with sinks to see if there are any artifacts
7. you can report back... the time it will take is going to be constrained by the size of the area in terms of cells that have to be processes and other computer stuff.  This is the type of thing that you would want to do on a well spec'd gaming machine... leaving your feable laptop to watch TV while you work

[curtvprice]

Yes, you are very impatient. I would wait longer than twenty minutes.

Also I would make sure that nothing else is running on your computer - flow accumulation is extremely RAM intensive, and if you are starving it of RAM by running other things at the same time it's going take longer.

[RachelDiPietro]

1. ESRI grid

3. Extent- min lat = 43.3751 min long = -89.7537 max long = -89.5010 max lat = 43.6261

6. DEM was projected and filled before doing Hillshade and Flow Direction.

7. I am using a campus computer in a school GIS lab for this assignment, and not my laptop.

I'll update again once I have more information. Trying Flow Accumulation again now, will give it until 6:30, after that I have to leave for the night. 

Thanks for your help!

[RachelDiPietro]

Actually not sure for 1., but I do know that it's not a TIFF file.

[DanPatterson_Retired]

The unprojected size is not relevant, it is the cell size and number of rows and columns of the projected raster that is important ... it will determine processing time

[curtvprice]

You can find this information by right clicking on your filled elevation raster, there you will find rows, columns (multiply them to get the number of cells) and the uncompressed size in MB. 

[JayantaPoddar]

Apart from closing other memory-intensive applications, you should also disable background processing from the Geoprocessing Options dialog box (Geoprocessing > Geoprocessing Options). Rerun the tool.

[MimyBiswas]

Hey Rechel...I was suffering from the same problem. My area was almost the entire Shillong plateau of India so it took me around complete 9 hours to to complete the Flow Accumulation. So I guess it depends on the area you are working on. I'm also new to all this software.