Watershed

Key Concepts

Understanding the following terms is helpful when working with watershed maps:

Catchment Basins: A basin (or catchment area) is a region where all water flows downhill across the surface to a common stream outlet.
Threshold (cells): To understand stream creation thresholds, it helps to know how Surfer defines a "cell." While a grid node is a single point, a cell in watershed calculations is a square or rectangular area centered on that grid node.
Depressions: Depressions are local pits or low points in the grid where water naturally accumulates because there is no downhill path to an outlet.

Watershed Properties

The watershed properties contains the following pages:

Map Properties

The map properties contains the following pages:

Adding a Map Layer

Watershed maps can be combined with any other map layer type (such as contour, post, or base layers) to display additional information. For example, overlaying a contour map on a watershed map helps visualize the topography that defines the catchment basins and stream paths.

To add a layer to an existing watershed map:

Select the Map object or the Watershed layer in the Plot window or Contents window.
Click the Home | Add to Map | Layer | [Layer Type] command (for example, Home | Add to Map | Layer | Contour).
Select the file or grid required for the new layer and click Open.

The new layer is automatically added to the existing watershed map axes.

To combine existing separate maps:

If you have already created a watershed map and a separate map (such as a contour map) using the Home | New Map commands, you can easily combine them. Simply click on the map layer (e.g., the contour layer) in the Contents window, hold down the left mouse button, and drag the map layer into the watershed map object. This creates a single map with two map layers using one set of axes and scaling parameters.

Any number of watershed maps can be combined with any other map layers.

Watershed References

Many of the parameters for the watershed map are technical in origin, and a detailed development is beyond the scope of this document. For additional information, see the following resources:

O'Callaghan JF, Mark DM. (1984) "The Extraction of Drainage Networks from Digital Elevation Data.” Computer vision, Graphics and Image Processing, Vol. 28, 323-344.

Wang, L. & H. Liu (2006) “An Efficient Method for Identifying and Filling Surface Depressions in Digital Elevation Models for Hydrologic Analysis and Modelling.” International Journal of Geographical Information Science, Vol. 20, No. 2: 193-213.

Garbrecht, J. and Martz, L.W. (1997) “The assignment of drainage direction over flat surfaces in raster digital elevation models.” Journal of Hydrology, Vol. 193, 204-213.

Welsh, D. J. A.; Powell, M. B. (1967), "An upper bound for the chromatic number of a graph and its application to timetabling problems." The Computer Journal, Vol. 10 (1): 85–86.

Jenson S. K. and J. O. Domingue. 1988. "Extracting Topographic Structure from Digital Elevation Data for Geographic Information System Analysis." Photogrammetric Engineering and Remote Sensing, Vol. 54 (11): 1593-1600.

Pierre Soille, Jurgen Vogt, and Roberto Colombo, 2003, "Carving and adaptive drainage enforcement of grid digital elevation models." Water Resources Research, Vol. 39, NO. 12, 1366.