Flow Accumulation Value

Question

1) What influence the flow accumulation value? How to cross check the accumulation result?

2) I made two separate flow accumulation processing. First, the output accumulation raster is saved by default GDB, it shows the value range between 0 - 6,852. Second, the output accumulation raster i saved in another folder (.tif file), the value range spike at 0 - 430,265. Why is it happened?

DanPatterson_Retired · Answer

Are your cell sizes and extents for the rasters the same between the comparisons?

Anonymous User · Answer

Hello,

I'll try and answer these questions below.

1) D8 Flow accumulation (without using weights), at a given cell (let us call this cell, pour point A) can be cross checked by looking at the cell count for a Watershed created for pour point A. This watershed can be created using the Watershed tool using the same D8 flow direction that was used to create flow accumulation raster and a raster or feature pour point representing pour point A.You can check the cell count by looking at the Raster Attribute Table after creating a Watershed.

In general,
Flow Accumulation value (at pour point A) = cell count of Watershed for pour point A - 1.

2) This is odd and I wouldn't expect the value ranges to be different for FGDB and TIFF rasters. Could you please share the input flow direction raster that was used to create flow accumulation with me and I can investigate this further. If the file is not too big, you can zip and upload it directly in this thread. Could you also mention what version of ArcGIS is used? and is it ArcMAP or ArcGIS Pro?

Best Regards,
Neeraj Rajasekar

For more information on how flow accumulation works please refer to this link.