Hydro Tools Ex

ARC HYDRO TOOLS An Extension in ArcGIS Environment for Terrain and Watershed Analysis Shane J. Prochnow, Ph.D. Center for Applied Geographic and Spatial Research Step 1: Convert your DEM into the proprietary ArcGIS .GRID format. Your DEM is often downloaded in a .DEM format. Go to the ArcToolbox (the little red icon on the standard toolbar of ArcMap), Conversion Tools, To Raster, and then select the DEM to Raster tool. It should look like this:

Navigate to where you saved the downloaded and unzipped .DEM file once you have opened the tool window.

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Step 2: Once you have your DEM converted and loaded into ArcMap, you should make sure the ArcHydro Tools toolbar is visible in ArcMap. Select View on the main menu bar, and then toolbars. Make sure ArcHydro Tools is selected as below:

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Step 3: The first step in a watershed analysis if to fill in the “sinks.” These are grid cells that are surrounded by grid cells of higher elevations. Go to the Hydrotools Toolbar, Terrain Preprocessing, Fill Sinks. Keep the default grid output names.

Your filled DEM will be called “Fil” and conveniently saved to its own folder in your working directory. Step 4: Now you must determine the flow direction for each grid cell in the DEM. This is essentially the steepest slope calculated in a nine cell cluster. Again, use the Terrain Preprocessing menu.

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Step 5: Now you must have the GIS calculate flow accumulations. Flow accumulation is the number of grid cells ‘upstream’ of it using the flow direction grid. Use the Terrain Preprocessing menu, again.

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Step 6: You can now define your stream network. Use the Terrain Preprocessing menu to define the stream network. The GIS will create yet another grid that defines the streams as grid code ‘1” and non-stream areas as no data.

A window will prompt you for a threshold number of grid cells in order to define a new stream. The default is 1% the maximum flow accumulation grid cell in the DEM extent. The larger the threshold, the few and larger the resulting catchments. Keep it at default for now. 5

Step 7: You can now define the stream segments using the Terrain Preprocessing menu.

Step 8: You can now create a catchments grid that corresponds to the stream segments using the Terrain Preprocessing menu.

Step 9: You can now vectorize the grided catchments using the Terrain Preprocessing menu. 6

Step 10: Now you can vectorize your stream network using the Drainage Line Processing tool in the Terrain Preprocessing menu.

Step 11: You can now create a point for each catchments outlet using the Drainage Point Processing tool in the Terrain Preprocessing menu.

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Step 11: Now play with the flown path and point delineation buttons on the ArcHydro toolbar. Make and refine your watershed delineation with at least two more new watersheds like below.

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