8.0 COMPLEX TERRAIN COMPONENT

        MEPAS is designed to consider environmental emissions of potentially hazardous materials. When such materials are released to the atmosphere at sites surrounded by flat uniform terrain, the atmospheric MEPAS component can be used to compute potential airborne concentrations and surface deposition rates. For sites with complex nonuniform surrounding terrain, additional enhancements have been added that allow for the influence of such terrain features. This section presents mathematical formulations and assumptions adopted within MEPAS for complex terrain applications.

        The complex terrain components described below are only approximations of the major consequences of local terrain effects on atmospheric transport and dispersion. In his overview of processes in complex terrain, Orgill (1981) describes specific terrain-induced airflow phenomena over various types of landforms along with the technical difficulty of modeling these phenomena. Case-specific models of flow in complex terrain tend to be computer-intensive models. However, such models were not considered appropriate for generating the long-term average concentration patterns needed in MEPAS.