Storm-enhanced sand transport in a macrotidal setting, Queen Charlotte Islands, British Columbia, Canada
Amos, C.L.; Barrie, J.V.; Judge, J.T. (1995). Storm-enhanced sand transport in a macrotidal setting, Queen Charlotte Islands, British Columbia, Canada, in: Flemming, B.W. et al. (Ed.) Tidal Signatures in Modern and Ancient Sediments. Special Publication of the International Association of Sedimentologists, 24: pp. 53-68 In: Flemming, B.W.; Bartholomä, A. (Ed.) (1995). Tidal Signatures in Modern and Ancient Sediments. Special Publication of the International Association of Sedimentologists, 24. Blackwell Science: Oxford. ISBN 0-86542-978-2. 358 pp., more In: Special Publication of the International Association of Sedimentologists. Blackwell: Oxford. ISSN 0141-3600; e-ISSN 2054-6610, more |
| Authors | | Top | - Amos, C.L.
- Barrie, J.V.
- Judge, J.T.
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| Abstract | This paper presents a method for the evaluation of regional sand transport patterns in a continental shelf setting, the inner Queen Charlotte Island shelf, western Canada. The method uses hydrodynamic and geological data sets of the region in a numerical model of sand transport (SEDTRANS). The model uses as input spatially variable bathymetry and grain size with time-variable surface gravity waves, tidal currents and wind-driven currents for a severe winter storm that took place on 26 February, 1984 (I: 5 year event). Bed shear stress is computed following the methods of Grant & Madsen ( 1979) and Grant & Glenn ( 1983). This shear stress is then used to estimate sand transport rate using thresholds of sand motion outlined in Amos et al. (1988) with a modified algorithm from Engelund & Hansen (196 7). Results conform with geophysical and geological observations on sand transport pathways. The tidal contribution to sand transport for the storm period accounts for only a small portion of the net sand transport in the region. Most of the predicted transport takes place as a consequence of the storm. As storms from the south-east typify this region, we conclude that such storms dominate the signature of sand transport. Under such storm conditions, coastal erosion of eastern Graham Island appears stimulated by high rates of coast-parallel sand transport. When the storm coincides with an ebbing tide, sand is predicted to move around Rose Spit and westwards into Macintyre Bay, where it is available for subsequent fairweather beach progradation. We interpret the observed decrease in coastal erosion (cf. Barrie & Tucker, 1992) in the south of the study region as largely due to the presence of an amphidromic point in the M2 tide, which induces beach accretion and the formation of log barricades. Rose Bar, located at the northern edge of Dogfish Bank, is interpreted to have formed as a result of storm-driven sand motion on the shelf, coupled with topographic steerage of both tidal and wind-driven flows and an associated sharp gradient in the sand transport rate at the bank margin. Thus, Rose Bar is the result of what we term a hydraulic fence to storm sand transport and is, therefore, a relatively stable feature. We conclude that Rose Bar is a nearshore storm ridge sensu Swift et al. ( 1981) which is the result of storm-induced continental shelf sand transport similar to that described by Amos & Judge ( 1991) for the east coast of Canada. In so far as these processes also led to the formation of Sable Island (Scotian Shelf), the development of Rose Bar may offer insight into the genesis of this enigmatic east coast feature. |
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