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MODELING FLOW PATTERNS IN A SMALL VEGETATED AREA IN THE NORTHERN CHICHUAHUAN DESERT USING QUIC ( QUIC URBAN AND INDUSTRIAL COMPLEX )
Citation:
BOWKER, G. E., D. GILLETTE, G. BERGAMETTI, AND B. MARTICORNEA. MODELING FLOW PATTERNS IN A SMALL VEGETATED AREA IN THE NORTHERN CHICHUAHUAN DESERT USING QUIC ( QUIC URBAN AND INDUSTRIAL COMPLEX ). ENVIRONMENTAL FLUID MECHANICS. Springer, New York, NY, 6(4):359-384, (2006).
Impact/Purpose:
The scientific modeling expertise of NERL/AMD technical staff often results in requests for staff to provide timely support and advice to EPA Management in the event of a national emergency and to perform the research on model development and evaluation in support of the development of early response models. Flow and dispersion in urban areas is extremely complex and not well characterized in spite of their importance to homeland security and emergency response applications. Specifically, understanding the transport and fate of pollutants in urban canopies is critical for implementing air quality standards, performing risk assessments, developing environmental management strategies, supporting human exposure and health effects studies. Recently, though, much focus has been placed on supporting the development of homeland security tools needed to prepare for and respond to malicious attacks with toxic chemicals. Toward this goal, laboratory studies have been conducted in EPA's Meteorological Wind Tunnel for idealized urban settings, for very complex settings such as lower Manhattan surrounding the World Trade Center (WTC) site, and for very building specific cases such as the Pentagon. Continued studies in a variety of urban morphologies and release scenarios are needed to support a more thorough understanding of urban dispersion and the development of refined numerical modeling approaches.
Description:
Sandstorms are frequent in the northern Chihuahuan Desert in New Mexico, an area characterized by open areas lacking vegetation, individual mesquite bushes, and mesquite coppice dunes. Field measurements of sand fluxes and wind velocities over a two year period provided a description of the area - suggesting that the "streets", the flat, elongated, non-vegetated areas aligned with the dominant wind directions are the principal sources of wind-dispersed soil and dust. However, since soil erosion and dust movement depend on the pattern, strength, and gradients in the wind field, modeling soil erosion and dust movement requires a continuous wind velocity field. Consequently, air flow patterns at this site were simulated using a semi-empirical mass-consistent diagnostic wind field model: QUIC version 3.4 (Quick Urban & Industrial Complex). 251 simulations were run encompassing several dust storms occurring in April 2003. Wind velocity vectors were compared between the model and field data at three heights for six locations and were found to correlate well for a majority of the situations suggesting that the flow patterns are consistent throughout the domain. In particular, good agreement was found for wind speeds at 0.75 m, the height for which the model was tuned. However, it overestimated velocities at 1.5 m (10% and 3.14 m (13%). Generally, the model successfully identified locations of the highest wind velocities and wind stresses, predominately found in "streets" aligned with the driving wind, and locations of wake flow downwind of mesquite bushes where there was separation flow or otherwise shelter from the wind.
