Watershed delimitation/delineation based on a DEM using ArcGIS Desktop

Here is a step-by-step tutorial on how to create a watershed delimitation based on a Digital Elevation Model (DEM) using ArcGIS Desktop:

Step 1: Obtain DEM data

1. Download DEM data for your area of interest from a reliable source such as the USGS Earth Explorer or the National Elevation Dataset.

2. Import the DEM data into ArcGIS by opening the ArcMap application and selecting File > Add Data > Add Raster.

Step 2: Preprocessing the DEM data

1. Ensure that the DEM data is projected in a coordinate system suitable for the area of interest by checking the data properties under the Layer Properties > Source tab.

2. Fill any sinkholes in the DEM data using the Fill tool. This ensures that all water flows are accounted for in the analysis. To do this, go to Spatial Analyst Tools > Hydrology > Fill and set the input raster to your DEM data.

3. Generate a flow direction grid using the Flow Direction tool. This tool assigns a direction of steepest descent for each cell in the DEM. To do this, go to Spatial Analyst Tools > Hydrology > Flow Direction and set the input raster to the filled DEM data.

4. Generate a flow accumulation grid using the Flow Accumulation tool. This tool counts the number of cells that contribute to each cell in the DEM. To do this, go to Spatial Analyst Tools > Hydrology > Flow Accumulation and set the input raster to the flow direction grid.

Step 3: Create the watershed delimitation

1. Determine the pour point location for the desired watershed. This is the location where water flows out of the watershed. You can select this point manually or use another method to derive it from other data layers.

2. Create a raster of the pour point location by converting it to a raster using the Feature to Raster tool. This converts the point location to a cell with a value of 1 in the raster.

3. Generate a watershed grid using the Watershed tool. This tool creates a raster grid where each cell is assigned to the watershed that drains into the pour point location. To do this, go to Spatial Analyst Tools > Hydrology > Watershed and set the input flow direction raster to the flow direction grid, the input pour point raster to the pour point location raster, and the input flow accumulation raster to the flow accumulation grid.

Step 4: Refine the watershed boundary

1. Convert the watershed raster to a vector using the Raster to Polygon tool. This tool converts the raster cells to polygons that define the watershed boundary.

2. Clip the vector polygon to the desired boundary using the Clip tool. This tool removes any portions of the watershed that extend beyond the desired boundary.

Step 5: Display and analyze the results

1. Add the clipped watershed boundary to your ArcMap project and visualize it using the symbology and labeling tools.

2. Perform any further analysis on the watershed boundary as needed, such as calculating the area, length, and slope of the watershed, or overlaying other data layers such as land use or soil data.

That's it! By following these steps, you should be able to create a watershed delimitation based on a DEM using ArcGIS Desktop.

These steps could be also introduced in a ModelBuilder