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Factors influencing the sedimentary environments of the Squamish River delta in southwestern British Columbia Bell, Leonard Montague

Abstract

The Squamish River Delta located at the head of Howe Sound, a glacial fjord, in southwestern British Columbia, is being formed by the deposition of sediments carried by the Squamish River and its main tributaries the Cheakamus and Mamquam Rivers. The river system drains an area of 1428 square miles generally underlain by granitic rocks. River flow is seasonal resulting in the intermittent deposition of sediments on the delta front. River training works constructed in 1972 have changed the hydrology of the river and influenced sediment transport and deposition. Channelization has resulted in increased deposition off the mouth of the west channel, and a marine transgression of 'the intertidal zone of the central channel. Hydrologic and oceanographic factors are the most significant of the natural processes influencing the sedimentary environments of the Delta. Estuarine circulation varies in relation to the dominance of river and tidal currents. Wind conditions are an important factor relating to the wave regime of the delta front. A comparison of bathymetric surveys made in 1930 and 1973 shows the delta front advancing at a rate of 21 feet per year, in the west and central sectors. Erosion is occurring at the head of the Mamquam Submarine Channel on the east flank of the central sector. A seismic profile survey in 1973 recorded the presence of large slump structures on the steep upper slopes of the delta front. These records indicate that the present delta is being built on a series of deformed and unstable sediments. Surficial sediment sampling of the delta front was carried out during and after the freshet of 1973. On the west sector, sands tend to dominate. These are fine to medium grained with large admixtures of silts and clays. The effect of flocculation on the differential settling of the suspended sediment may be an important factor contributing to the presence of clays on the delta front. The effect of port and industrial development on the aquatic ecosystem is currently being studied by research scientists from the Department of the Environment. Land fill and dredging has resulted in the loss of vegetation and benthic algal mats. Habitats of the benthic invertebrates, the primary source of food for juvenile salmon, have been disrupted and are threatened by future development. The need for inter-disciplinary studies combined with a continuing program of data collecting, is necessary to fully understand the factors influencing the formation of the Squamish River Delta and to evaluate the effect of future development.

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