Flow Accumulation Generation problem

[SamHuang]

Can someone explain what are the possible problems to why when i run my flow accumulation processing tool, it does not output the flow accumulation correctly. Let me provide you an image to show you what i'm talking about. As you can see within the attachment there is an image which shows the flow accumulation but it does not show entirely of where all the streams are flowing. The circled area are missing for whatever reason and I can't seem to find out what the reason is and how to solve this problem

Thanks in advance!

[ShaunWalbridge]

Try changing the symbology on your raster to include all the values in your range, and you should see the smaller flow accumulation values. Generally, it's most useful to visualize the flow accumulation after thresholding the data, as is being done in the image you attached.

cheers,
Shaun

[SamHuang]

Part of me trying to generate a proper flow accumulation is so that i can eventually generate watershed in which allows me to determine where the upstream and downstream are. But based on this flow accumulation, it ended up having problem with generating the watershed. The result looks like the attached image.

Base on this even if there is a small value, it would not make sense as i know for a fact that stream flow through it, but the accumulation does not show.

[SamHuang]

The reason why I'm asking this is i need to generate a proper flow accumulation  so that i can eventually generate watershed in which allows me to determine where the upstream and downstream are. But based on this flow accumulation, it has been causing a lot of problems generating the watershed. The result looks like the attached image. [ATTACH=CONFIG]25472[/ATTACH]

Base on this even if there is a small value, it would not be acceptible as I know for a fact that the stream flow through it, but the accumulation does not show.

[SamHuang]

this is the resulting watershed that i have generated from the accumulation flow. Clearly you can see that it did not generate an upstream or downstream properly

[JanetBrewster]

Maybe you're missing a step? This is what I do to create watersheds:
1) Fill
2) Flow Direction
3) Flow Accumulation
4) Stream Link [via Raster Calculator: "StreamLink (SetNull (FlowAccumulation < n, FlowAccumulation), FlowDirection)", where n is 1% of max flow accumulation but the smaller the number the more stream segments you'll get] -- results in the StreamNetwork raster that I use in step 5
5) Watershed [via Raster Calculator: "Watershed (FlowDirection, StreamNetwork)"]

Janet

[SamHuang]

unfortunately there are no steps missing. I know this for a fact, because there are 70+ watersheds that I have to generate and most of them seem to work with the exception of a few that did not generate properly. It's something that i've been very puzzled about it.

[ShaunWalbridge]

Sam,

Can you provide a small sample of data that contains the issue you're seeing?

cheers,
Shaun