Watershed delineation with ArcGIS

For automatically define a watershed, it is necessary to properly define their boundaries, considering upstream from an outlet point, and are usually demarcated by mountain ridges. A good advantage is that ArcGIS permit to run hydrologic analysis tools, then makes work easier, a good advantage is that ArcGIS permit to run hydrologic analysis tools, making job easier, for this example you can download the files for practice, other option is it download a DEM from Aster GDEM, NASA Reverb or LP DAAC Global Data Explorer, if you can make your own DEM also it is possible.

Watershed delineation with ArcGIS

Then we will show you step by step how to automatically delineate a watershed.

Remove imperfections (holes and sinks) of the raster with the Fill tool.

ArcToolbox > Spatial Analyst Tools > Hydrology > Fill

Fill ArcGIS Hydrology

Establish hydrological flow direction of the slope with the Flow Direction tool.

ArcToolbox > Spatial Analyst Tools > Hydrology > Flow Direcction

Flow Direcction ArcGIS Hydrology

Determine the accumulation flow cells, each cell flowing down the slope through of the tool Flow Accumulation.

ArcToolbox > Spatial Analyst Tools > Hydrology > Flow Accumulation

Flow Accumulation ArcGIS Hydrology

If everything goes right we have a raster as shown in the figure below.

Flow Accumulation ArcGIS Hydrology

Now we will build the drainage network automatically, through of a conditional (this depends on the size of the raster in “Input true raster or constant value” place the unit 1 point output directory is now very important in “Expression” using the expression value> 400, this value depends on the size of the pixel and the raster, the larger the watershed to use a higher value, another option is to use Raster Calculator) using the Con conditional to classify the cells with flow accumulation greater than a threshold specified by the user, for example to enter a low value results show small tributaries drain network, but the higher the value the drainage get larger.

ArcToolbox > Spatial Analyst > Conditional > Con

Con ArcGIS

As a next step to generate a vector of the result from the raster of accumulated flow and conditional, using the Stream to Feature tool.

ArcToolbox > Spatial Analyst Tools > Hydrology > Stream to Feature

Stream to Feature ArcGIS Hydrology

The next step to determine the drainage point of the watershed, this can be done by creating a point shapefile type, then interpolate a digital elevation model (TIN or DEM) to obtain three-dimensional coordinates.

ArcToolbox > 3D Analyst Tools > Functional Surface > Interpolate Shape

Punto de desfogue en ArcGIS

To conclude with the Watershed tool, using the Flow Direction raster created and interpolated discharge point.
ArcToolbox > Spatial Analyst Tools > Hydrology > Watershed

Watershed en ArcGIS

Finally to obtain the watershed polygon just enough to convert the raster to polygon shapefile type.

ArcToolbox > Conversion Tools > From Raster > Raster to Polygon

The result of the delineation of the watershed is shown in the figure below.

Watershed delineation

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