ISCST3 Tech Guide

Gaussian Plume Air Dispersion Model

6.5 ISC Complex Terrain Screening Algorithms

The Short Term model uses a steady-state, sector-averaged Gaussian plume equation for applications in complex terrain (i.e., terrain above stack or release height). Terrain below release height is referred to as simple terrain; receptors located in simple terrain are modeled with the point source model described in Section 1.1. The sector average approach used in complex terrain implies that the lateral (crosswind) distribution of concentrations is uniform across a 22.5 degree sector. The complex terrain screening algorithms apply only to point source and volume source emissions; area source and open pit emission sources are excluded. The complex terrain point source model, which is based on the COMPLEX1 model, is described below. The description parallels the discussion for the simple terrain algorithm in Section 1.1, and includes the basic Gaussian sector-average equation, the plume rise formulas, and the formulas used for determining dispersion parameters.