Model Types and Definitions
The simulation models are classified as follows:

1. Hydrologic (Watershed) Models: models that simulate the basin runoff to determine the flood hydrographs resulting from natural or synthetic storms such as HSPF, HEC1, SCS program TR, models from Universities (Texas, Kentucky, Ohio, Stanford, etc.).

2. Hydraulic (Hydrodynamic) Models: models that simulate the hydraulics (flows, stages and velocities) in rivers and lakes (1, 2 or 3-D steady or unsteady state). Examples: Corps HEC1 / RAS and 1-D unsteady flow models such as Corps= UNET, programs developed by NWS(Fread), TVA=s program (SOCH), USGS and several other programs developed at universities and private industry; 2-D or 3-D finite difference and finite element models such as Corps TABS, other models from universities (UC, SUNY, UT, Swansea etc.)), Rand Corp. (Lindertse).

3. Sediment Transport Models:

1. Models that simulate the processes of erosion and deposition of non-cohesive or cohesive sediments in channels and reservoirs such as Corps HEC-6, QSNET, TABS, etc.
2. Models that determine the total sediment yield from the watersheds such as program developed by Soil Conservation Service, USBR and universities. Many of the existing sediment transport models are stand-alone and some are combined with the hydraulic models for convenient use.

4. Contaminant Transport Models: models that simulate the processes of conservative chemical / radioactive / thermal effluent dispersion in channels or lakes. This includes the simulation of adsorption / desorption / decay / erosion / deposition / transportation of contaminated bottom and suspended sediments. These models are generally decoupled from the hydrodynamic models.

Any of the above models with convenient Data Analysis and Graphical Interface Software would be useful tools. Although data requirements for specific or individual models vary depending on their complexity or purpose, it is possible to describe the data requirements in general.

For more information, see Characterization of Simulation Models (PDF).
Source: Compendium of Tools for Watershed Assessment and TMDL Development, U.S. EPA Report, May 1997, (EPA841-B-97-006); and U.S. Army Corps of Engineers, Hydrologic Engineering Center, Report TD 36.