topic Re: Flow Direction raster is speckled in ArcGIS Spatial Analyst Questions

Flow Direction raster is speckled

AlmaA — Tue, 08 Dec 2020 22:31:29 GMT

Hello,

I have a 10m DEM that I need to create a flow accumulation raster from. So I did the following: 1) filled sinks using "FILL" tool; 2) ran "FLOW DIRECTION" on the filled raster; 3) ran "FLOW ACCUMULATION" on the flow direction raster.

The flow accumulation raster seems wrong as it is mostly all one color (one value) and does not show any streams. I believe this is due to my flow direction raster which is highly pixelated (see below), although the values do make sense (2, 4, 8....).

In my experience, flow direction outputs have larger polygons and dont look as "speckled".

Any insight? I am using ArcMap 10.8

Re: Flow Direction raster is speckled

DanPatterson — Tue, 08 Dec 2020 22:56:31 GMT

What were the units of the dem? All the same for X, Y and Z?

I assume you followed the recommended procedure in the help.

If you have access to Pro, there are more options for flow direction that may be of use for your terrain.

Flow Direction (Spatial Analyst)—ArcGIS Pro | Documentation

Re: Flow Direction raster is speckled

AlmaA — Wed, 09 Dec 2020 22:05:21 GMT

Units are meters, and I believe it is for X, Y, and Z. I obtained DEM from USGS NED. What worked was clipping the DEM. Maybe the edges were throwing things off?

I am now having trouble creating the FD and FA rasters from a LiDAR derived DEM that is 2ft resolution. I am going to try clipping the edges with this one too.