Forest Investment Account (FIA) - Forest Science Program
FIA Project Y051276

    Numerical modelling of wind flow in retention system openings [2005 Project Description Only]
 
Imprint: Vancouver, B.C. : University of British Columbia, 2005
Subject: Forest Investment Account (FIA), Windfall (Forestry), British Columbia, Winds, Mathematical Models
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
Trees retained in partially harvested areas or along the boundaries of new harvest areas are susceptible to wind damage in British Columbia's windy climate. A key requirement for both empirical and mechanistic windthrow risk models is to predict wind speed and direction at canopy height within harvested openings. The objectives of this study are 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 were simulated using high-resolution large-eddy simulation (LES) code, using terrain-following coordinates. LES models can take their initial and boundary conditions from numerical weather prediction (NWP) simulations having 3 km horizontal grid spacing for synoptic systems known to generate high winds. In year 1 our focus was on validating the LES model by running scenarios for which we had wind tunnel results from earlier experiments with model forests. We are satisfied that LES produces similar results for these scenarios. We also worked out procedures for data archiving and exchange. We completed NWP re-simulation of 5 recent wind events during which wind damage was reported in south-western BC. As of November 1, 2004 we began archiving the hourly NWP forecast results for the southern BC domain at 3 km grid spacing. In discussions with the UK Forestry Commission, we laid the ground-work for incorporating project results into the ForestGALES mechanistic windthrow risk model. In year 2, we will run a series of high resolution LES simulations to represent windflow for case studies that represent a range of harvesting, canopy and terrain conditions. Results of these simulations will then be used to develop simplified equations that relate local overspeed ratios to directional fetch, canopy and terrain properties. The utility of these simplified equations for windthrow prediction will be tested using a recently developed empirical windthrow risk model and GIS dataset for southwest Vancouver Island. Once validated, these simplified equations will be incorporated into the ForestGALES mechanistic windthrow risk model to enable prediction of windthrow risk for complex partial cutting scenarios.
Stephen J. Mitchell.
Related projects:  FSP_Y062276
Contact: Mitchell, Stephen J., (604) 822-4591, stephen.mitchell@ubc.ca

Updated August 16, 2010 

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