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I have lidar imagery for a watershed and am trying to process it so that a landowner know if they can hold water on their property or where they can hole the water (this is the more important part).
I've tried some of the hydrology tools and I am not sure if I am using them right or if they are not working with my data. I've tried the flow direction tool and that seems to work correcly but I have also tried the sink tool and the fill tool and I think that these are some of the tools that I want but Im not entirely sure if I'm using the right or exactly what they do and ESRI's description doesn't help me. The Sink tool gives me a bunch of little dots, it doesn't tell me much unless I'm misinterpreting the data.

the picture is of the flow direction tool outcome and the sink tool outcome(pink).

I have also tried the flow accumulation tool but that also didnt give me very useful results Flow Accumulation outcome

If there are other ways of using these tools or other tools to use any advice and tips would be greatly appreciated.

Edit:I should mention that the whole area is relatively flat with minimal elevation change, the section of land that I am looking at (pictured below) has an elevation change of 0.5-1m from the NW to the SE (approximately) and that I want to be able to use this process for other pieces of property.

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It would be a good idea to incorporate soil types after you've determined low points. You can get soils data here: websoilsurvey.nrcs.usda.gov/app/HomePage.htm –  Paul Apr 24 '13 at 16:56
    
unfortunately the USDA site wont help me as I'm in Canada and so is the land, I do have the soil Information although the area is relatively unchanging, partly to the area I am in and partly because it is a 'small' area that I'm looking at(about half of a section) –  heather Apr 24 '13 at 17:01

1 Answer 1

As a preface: LiDAR data is really hard to work with when you're trying to build watersheds and basins because it is nearly too accurate. It can result in thousands and thousands of tiny basins. There are, however, ways to work with it. Further, this is probably only a partial answer because I don't know much about soil types and infiltration, but I assume you want to identify the areas that provide the greatest water accumulation with the lowest infiltration, or the greatest water accumulation and highest infiltration.

The little dots you see when you use the Sink tool are the points to which the surrounding area flows. If you want to easily visualize this, run the Basin tool to get the microwatersheds and put the Sink layer on top. You will see that each of these microwatersheds has one point, the Sink representing the lowest area in the Basin.

The Fill tool literally fills these sinks--it generalizes the DEM to smooth out the sinks so you can build larger basins.

I would try a number of things depending on what you're trying to accomplish and the size of the property you're looking at:

First, run the Flow Direction tool. The grid produced here doesn't really show anything interesting visually, but you need it to run Flow Accumulation. This tool will tell you "how much" water will accumulate at the lowest points in the grid--with this, you can identify areas into which the most surface water will flow. Run the Basin tool--this will delineate these areas.

That might work, but chances are, you have hundreds, if not thousands, of these basins. This doesn't help you identify the areas of greatest flow. If you can't immediately identify areas, try this: Run the Fill tool on your LiDAR DEM. This will fill the sinks mentioned above and smooth out the terrain. Then repeat the process--Flow Direction -> Flow Accumulation -> Basin. Here, you should be able to more easily identify basins. If I were doing this project, I would identify the area of highest accumulation in the largest basins. This should tell you the best site for a retention pond, assuming it fits the soil type profile you're looking for.

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The First time I read this it didn't make sense to me, now I wish I had taken more to read it carefully, it would have saved me a lot of time and agrivation. This is exactly what I needed, thanks so much. I was wondering if you might know of any online Lidar training or schools or something that offer online training. I've taken the ESRI courses and they were helpful for setting things up but not for processing and using the lidar data, any suggestion would be greatly appreciated –  heather Mar 11 at 19:15
    
I'm trying to remove the zero values in the data, I have no clue how. I am trying to have a layer with just the streams derived from the processing. –  heather Mar 11 at 19:35
    
Sorry for the slow response. Are you trying to remove zeros from the flow accumulation grid? The easiest way I've found is to use the reclassify tool and set an arbitrary threshold (based on the data you're using) and then use the stream to feature tool. You can explore other spatial analyst tools, like stream order, depending on what you're after. –  Wes Mar 17 at 19:42
    
I am trying to eliminate the zero values from a sink-fill layer. My steps were 1) sink-fill operation on the Lidar data 2) subtract 30 cms to eliminate small depressions that may not be large enough to hold a reasonable amount of water, the next step that was suggested was to eliminate the zero values to reduce the data, once the zeros are eliminated the next suggested steps are to run the region group tool to combine adjacent potential storage cells and then summarize the sink volumes. –  heather Mar 18 at 13:26

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