Methods to Identify Sinks

05-01-2017 11:25 AM
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Methods to Identify Sinks

I am new to Arc Hydro (AH), and have been working to Identify Sinks in the landscape. I encountered several issues, so I wanted to share my methods in hope this saves someone else the time I spent trying to figure this out. I started my project with raw Lidar and processed it using Quick Terrain Modeler, which resulted in 10 subset DEMs in a .tif file format for just one county. I did not mosaic the subsets, because I later learned that a county-level DEM is far too large to process in AH. Many of these tips were compiled from the AH Tutorial found online, Geonet AH Problem Solvers, and the developers of AH. I used ArcMap 10.4. 

*before starting make sure you have downloaded the correct version of AH for your system, and make sure your computer has the hardware/software needed for this level of geoprocessing. You will need a Spatial Analyst license. 

1) Create a folder on your local machine, i.e., C:\GIS\project    *When using AH, always work on the local machine, keep names and pathways short and simple. 

2) Open ArcMap, select My Template/Blank Map, and designate geodatabase for this map, i.e., C:\GIS\project\project.gdb

3) Turn on Spatial Analyst and AH tools
    Customize > Toolbars > Arc Hydro Tools
    Customize > Extensions > Spatial Analyst

4) Turn off Background Processing
    Geoprocessing > Geoprocessing Options > Background Processing > Uncheck "Enable" > OK

5) Set Processing Extent
    Geoprocessing > Environments > Processing Extent > Navigate to the DEM you will be processing > OK

6) Clean User's Temp Folder
    AH toolbar > ApUtilities > Additional Utilities > Clean User's Temp Folder > Yes > OK

7) Set Target Locations
    AH toolbar > ApUtilities > Set Target Locations > ApUtilitiesConfig > OK > make sure this location is correct
    AH toolbar > ApUtilities > Set Target Locations > HydroConfig > OK > make sure this location is correct 
    *Rasters should go into a folder (no .gdb) and Vectors go into a .gdb

😎 Add your DEM raster to the map, build pyramids if prompted. 

9) Save map
    File > Save As > navigate to C:\GIS\project and save map, i.e., project.mxd

10) Preprocess the DEM if necessary. The raster format that I found to be most useful included: a small raster (columns and rows < 10,000x10,000), integer (not floating point), GRID format, defined Z coordinate system, and NoData values converted to "0". I started with a 32-bit, floating point, .tif raster, so I had to preprocess the raster before running it in AH:  
    a) Original DEM Float to Integer
         Spatial Analyst > Math > Int
         Output Location: C:\GIS\project      *I added "i" to the end of the file name, so I knew which raster this was from the others,             i.e., "projecti.tif"
    b) DEM .tif to GRID
         Conversion > to Raster > Raster to Other Format
         Output Location: C:\GIS\project 
    c) Define Projection
        Input: DEM GRID in an integer format (from previous step)
        Open coordinate system list, Spatial Reference Properties > select Z Coordinate System tab > select NAVD88 > double-               click NAVD88 > Vertical Coordinate System Properties window will open > and change Linear Unit Name: centimeters >                Apply > OK > OK > OK
         *This step changes the coordinate system of the input file and does not create an output. 
    d) Raster Calculator, convert NoData to "0"
         Spatial Analyst > Map Algebra > Raster Calculator
         Use this equation for the raster: Con(IsNull("inputraster"),0,"inputraster")
         Output: C:\GIS\project\projectc      *I added a "c" to the end of the name, so I knew this is the calculated version of the                  raster. 

11) Remove the other files that may have been added to your map except for "projectc" file (this should be the raster that is: integer, GRID, defined projection, and NoData=0). It wouldn't hurt to save your map again, and clean your temp folder one last time before running AH. 

12) Sink Prescreening
     Terrain Preprocessing > DEM Manipulation > Sink Prescreening
     Input: projectc

*Save your map and clean your temp folder*

13) Sink Evaluation 
     Terrain Preprocessing > DEM Manipulation > Sink Evaluation 
     Input: PreFillDEM

*Save your map

I followed all of the above steps, and still could not get a successful output with Sink Evaluation and the issue turned out to be my computer's graphic/video card. It worked perfectly once I ran it on a more robust machine.