ABSTRACT: Flow hydraulics, bedforms and macroturbulence of Squamish River Estuary, British Columbia

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Abstract

Recent studies emphasize that a better understanding of relations between sediment transport, riverine/estuarine flows and acroturbulence will improve predictions of flow resistance and sediment transport. Macroturbulent features (e.g. boils) have been related to specific bedform or hydraulic conditions which are found in Squamish River estuary. Study aims included: (1) establishing predictive models for bedform parameters based on hydraulic and tidal variables and (2) relating boil characteristics (e.g. period, sediment entrainment) to hydraulic, tidal and bedform conditions. Predictive models for mean bedform-height (h) and wavelength (w) xplained up to 75% of the variance in h and w. Outliers tend to occur on days of tidal-height maximas or minimas in the fortnightly tidal cycle. Bedform h is more sensitive to flow variations than w, and his sensitivity is inversely related to water depth. Observations of boil production, morphology, intensity and duration indicate that there are two types of boils in the estuary. Boil-production mechanisms could not be determined, but scaling parameters for both types are suggested. As h > 0.5-0.6 , the relation with w becomes strongly inear, and Type 1 boil intensity and sediment entrainment also increase sharply. This may suggest that bedforms become hree-dimensional as scour holes form on the lee side. Sediment entrainment within Type 1 boils is also noted to be dependent on water depth. Type 1 boil period (t) also decreases rapidly as relative roughness (RR) increases, becoming asymptotic at t = 1-10s as RR > 0.2. Time series of streamwise current-speed display patterns also noted in simultaneous video footage of Type 2 boil eruptions at the water surface. Correlation of the time series suggests that boil period is not governed by speed, but there may be a feedback relation such that intense boil activity within the water column increases flow resistance, diminishing current speed and affecting boil production.

Bibliography of Canadian Geomorphology