Forest Investment Account (FIA) - Forest Science Program
FIA Project Y062276

    Numerical modelling of wind flow in retention system openings [2005/06 Project Description Only]
 
Imprint: Vancouver, B.C. : University of British Columbia, 2006
Subject: Forest Investment Account (FIA), Trees, Effect of Wind On
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
The objectives of this study were to characterize wind behaviour during windstorm conditions in harvested openings of various shapes and sizes, with and without residual trees, in simple and in complex terrain. Wind speeds within and immediately above the canopy were simulated using high-resolution large-eddy simulation (LES) code, using terrain-following coordinates. We also used numerical weather prediction (NWP) simulations to characterize windflow across southern BC. We validated the LES model by running scenarios for which we had wind tunnel results from earlier experiments with model forests and then examined the effect of increasing aggregate width and spacing between aggregates on the maximum moment experienced in rows of aggregates downwind of a cutblock boundary. We used NWP to re-simulate several strong wind events that occurred during the years from 2000-2003. From October 1, 2004 to October 6, 2005 we archived the hourly NWP forecast results for the southern BC domain at 2 km and 4 km grid spacing and obtained wind speed and directional data for the top 5 events, and Weibull parameters for estimating extreme wind return periods. We adapted the UK ForestGALES mechanistic windthrow risk model and developed the program WINDFIRM to enable incorporation of NWP and cutblock design (fetch and boundary orientation) results. The NWP and updated cutblock design variables were added to an existing GIS-based dataset for the West Island Timberlands operation on southwest Vancouver Island. The utility of these new variables for improving cutblock edge windthrow risk prediction was tested. Adding variable retention fetch and peak wind variables improved the predictions for windthrow prediction. Before ForestGALES_BC can be properly validated against field results it will be necessary to build-in the capacity to make predictions for multi-storied, multi-species stands.
Stephen J. Mitchell.
Related projects:  FSP_Y051276
Contact: Mitchell, Stephen J., (604) 822-4591, stephen.mitchell@ubc.ca

Updated August 16, 2010 

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