based on the diffusion (noninertia) form of the governing flow equations. Similarly, channel flow is modeled using a one-dimensional unsteady flow hydraulic model based on the diffusion type equation. The resulting models both approximate unsteady supercritical and subcritical flow (without the user predetermining hydraulic controls), backwater flooding effects, and escaping and returning flow from the two-dimensional overland flow model to the channel system.

This report is organized into five sections as follows:
1. DHM model theoretical development,
2. Verification of the DHM model,
3. Program description for the DHM,
4. Applications of the DHM, and
5. Comparison between the DHM and the simpler kinematic routing technique.
In this report, the pertinent literature is cited as needed in the text. However, for a general overview, the reader is referred to the Two-Dimensional Flow Modeling Conference Proceedings of the U. S. Army Corps of Engineers (1981).

The diffusion hydrodynamic model computer code can be easily handled by most current home computers that support a FORTRAN compiler, FORTRAN listings (and documentation) are included for the reader's convenience.

In typical applications involving large scale problems, pre- and post-processors should be developed to ease the data entry demands, and graphically display the tremendous amount of modeling results generated by the computer models.