| Summary: | Previous studies (Jackson, 1993) suggest an outflow wind, which flows below an
inversion in a well defined layer through Howe Sound, may exhibit hydraulic behaviour.
Strong outflow winds in Howe Sound are simulated in the laboratory using a single fluid
layer in a small scale one-dimensional physical model. Model results are presented and
compared with observations recorded in Howe Sound during a severe outflow wind event
in December, 1992. Field observations affirm the findings of the physical modelling with
both indicating the presence and location of controls and hydraulic jumps in the wind
layer. Hydraulic behaviour is found to change as the synoptic pressure gradient and the
flow rate increase. An additional comparison is made with output from the computer
model, Hydmod of Jackson and Steyn (1994b). Numerical simulations, configured for
the conditions present in Howe Sound during the December, 1992 event, indicate channel
hydraulics (and thus spatial wind speed variation) closely resembling the physical model
and field results.
Outflow winds are studied in more detail through a series of experiments conducted with
a three-dimensional physical model which is geometrically and kinematically similar to
the prototype, Howe Sound. The results reveal the structure of the wind layer over a wide
range of possible field conditions. Hydraulic features, which do not behave in a
traditionally one-dimensional manner, are identified. The 3D model results, although
more detailed, verify the findings of the 1D modelling in general. Together the results
provide a predictive tool for determining hazardous zones of extreme wind during an
outflow event. === Applied Science, Faculty of === Civil Engineering, Department of === Graduate
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