Diffusion in a Canyon Within Rough Mountainous Terrain

Open Access
Publisher Website
Google Scholar
Abstract
An accelerated field measurements program was conducted to quantify atmospheric diffusion within a deep, steep-walled canyon in rough, mountainous terrain. Two principle objectives were pursued: impaction of plumes upon elevated terrain, and diffusion of gases within the canyon versus diffusion over flat, open terrain. Oil fog flow visualizations provided qualitative information; quantitative diffusion measurements were obtained using sulfur hexafluoride gas with analysis by highly sensitive gas phase coulometric techniques. Eleven 45 to 60 min gaseous tracer releases were conducted. Stability-category-related differences in canyon diffusion versus flat terrain diffusion were found. Daytime lapse conditions showed little difference. Neutral stability tests showed five times greater dilution for canyon axial concentrations; strong inversion tests resulted in canyon plume centerline dilutions fifteen times greater than calculations using parameters derived for flat terrain. Plume effluents frequently impacted against elevated terrain. Enhanced mechanical turbulence associated with gradient wind-flows near the mountain tops, density flows originating in side canyons, and turbulent wakes from pronounced terrain irregularities within the canyon are believed to be some of the additional physical mechanisms affecting plume dilutions in Huntington Canyon. The present results should be relevant, at least qualitatively, to similar deep, steep-walled canyons. They should not be applied indiscriminantly to sites with less extreme topography. Additional measurements are needed at sites in less rugged terrain. Highly buoyant plumes may require special study since buoyancy may be in competition with postulated effects from the enhanced mechanical turbulence observed within the rough terrain setting.

This publication has 0 references indexed in Scilit: