What does the output value of the Sink Tool mean?

[SiyangTeo]

Hi, I just used the Sink geoprocessing tool to identify the Sinks in my Flow Direction model

How do I know what the depth of the sink is so that I can fill up the false positives? The attribute table has a field called values, and it ranges from 5,000 to 7,000 plus. Does this indicate the depth, and if so, what unit of measure does that represent?

Thank you.

[NeilAyres · Accepted solution]

See this page "How sink works".

http://resources.arcgis.com/en/help/main/10.2/index.html#//009z00000065000000

It also tells you how to find out how deep they are.

[SiyangTeo]

Thanks Neil,

I have read this page. It says that the Sink tool is supposed to return the depth. However, it did not say what is the unit of measurement. Any ideas?

Thank you,

[DanPatterson_Retired]

in the input units of the raster...however, I suspect that you were determining sinks in a grid with geographic coordinates (aka decimal degrees) with elevation values in meters or feet...if this is the case, always project your rasters so that X,Y and Z are in the same units.  If this is not the case, then you have some bizarre values in your DEM which should be filtered prior to determining the sinks.

[JayantaPoddar]

Hi Siyang,

If you want to fill the sink, you could use Fill (Spatial Analyst) tool on the original DEM.

Thanks,

Jay

[DanPatterson_Retired]

I think he is examining the sinks,  Fill will just fill them without any care about the nature of the sinks.  In this case, there are some problems with the identified sinks that need to be rectified before using the Fill option

[SiyangTeo]

Thanks Pat, you know exactly what I am thinking.

I just did a check and the sinks are at a projected coordinate system same as the DEM and flow direction model. I went to look at some localities at the DEM where the sink occurs, and they are showing normal values of which I presumed to be in meters.

At a lost now, wondering what I did wrong. 😕

[JayantaPoddar]

Hi Siyang,

As far as I know, the output of the Sink tool is an integer raster with each sink being assigned a unique value. Sinks are numbered between one and the number of sinks. The values of the output Raster do not represent the depth, but the sink number. One sink may have multiple pixels.

[SiyangTeo]

Hi Jayanta,

You are right. This is stated in the Help guide too. I guess I was confused at its guide (ArcGIS Help (10.2, 10.2.1, and 10.2.2) which states that the Sink Tool gives "a raster of sinks coded with depth".

Now I realised that it requires several rounds of processing as stated in the page to derive the actual depth.

Thank you!

[DougHaller1]

I agree this is confusing. After researching and reviewing the online resources and examples of non-esri workflows, I do not understand how one interprets the results of the Sink tool. How do we know if there are or are not sinks by looking at either the image/raster or the attribute table?