| Geog 312: Natural Hazards | ||||||||||||||||||||||||||||||||||||||
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| Coastal hazards exercise | ||||||||||||||||||||||||||||||||||||||
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| The Point Grey - Richmond shoreline case. Assignment 1. The susceptibility of cliffs to erosion depends on their erodibility and the local wave climate. In the case of Point Grey, the glacio-fluvial deposits of the Quadra Sands are highly erodible. Use the map of the Strait of Georgia and the wind rose, and the wave height forecasting chart, to answer the questions below. a) What is the percentage of time that cliffs may be under direct wave attack (= the proportion of onshore [NW-W-SW] to offshore/alongshore winds)? b) What is the fetch along exposed azimuths in the Strait of Georgia? (Estimate to nearest 10 km) NNW NW WNW W WSW SW WSW c) What is the significant wave height (=mean height of the highest 33% of waves in a wave train) that would be generated by 40 km/h winds (Beaufort scale 6; a "strong breeze"), blowing from the SW, W, and NW in the Strait? d) What is the significant wave height associated with the maximum extreme hourly winds recorded at Vancouver International Airport (westerlies clocked at 89 km/h [Beaufort scale 9/10; a "strong gale"])? 2. Wave energy (the ability of the waves to do work) is proportional to the fifth power of wave height. What is the relative amount of energy generated by waves produced by a "strong breeze" versus a "strong gale" in the Strait of Georgia? (see Table 1) Table 1. Wave energy (arbitrary units) as a function of significant wave height.
Discussion Critically examine the current proposals for Point Grey and assess coastal hazards on Fraser delta shorelines. Questions to consider: What mitigating measures have been tried to date? How is future sea-level rise likely to affect risks in this area? Are there significant tsunami risks? What mitigation efforts can you suggest? What emergency plans would you put in place? |
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