Contemporary Squamish River sediment flux to Howe Sound, British Columbia

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Abstract
Squamish River drains 3600 km2 in the southern Coast Mountains of British Columbia to Howe Sound at Squamish, some 50 km north of Vancouver. This study uses differencing of digitized bathymetric surfaces based on the Canadian Hydrographic Services surveys of 1930, 1973, and 1984 at the head of Howe Sound to yield a long-term sedimentation rate for Squamish River delta. The sediment flux from Squamish River to Howe Sound is determined to be 1.29 × 106 m3 a−1 or 1.81 × 109 kg a−1, rates consistent with loads calculated from flow and sediment-concentration regimes measured in the estuary in 1973 – 1975 and 1987 – 1988. The latter data indicate that the modal discharge-effectiveness class is 600 – 700 m3 s−1, moving 13% of the annual suspended-sediment load. Discharges up to 1400 m3 s−1 constitute 99.8% of all flows and are responsible for transporting 81.5% of the annual load. A very significant 18.5% of the load is moved by large-magnitude floods (> 1400 m3 s−1), which occur less than 0.2% of the time.Squamish Delta is prograding downfjord at an average rate of 3.86 m a−1 although local extensions of the delta front in a given year may approach 20 m. Some of the geomorphic implications of extrapolating these contemporary rates of fjord infilling over the Holocene are discussed briefly.

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