TIDAL WAVE REFLECTANCE, EVOLUTION AND DISTORTION IN ELKHORN SLOUGH, CA

摘要

The shoreward and seaward propagating tidal wave components were determined using four co-located pressure and velocity sensors longitudinally deployed in Elkhorn Slough, Monterey Bay, CA, to describe tidal wave evolution and distortion. Elkhorn Slough is short, reflective (~100%) estuary consisting of a narrow, gently sloping main channel and vast marsh and mud flats near the landward boundary. The amplitude reflection for the astronomical tidal constituent is ~90%, whereas the distortion, described by summing all non-astronomical tidal amplitudes, reflection is large (125%) for all stations stating that the seaward tidal wave is more distorted than the shoreward tidal wave. It was found that the reflective time, defined as the time it takes the tidal wave to propagate to the landward boundary and back, varies as function of tidal elevation. Surprisingly, the reflective time increases with increasing tidal elevation contrary to the hypothesis that the shallow-water tidal wave phase speed increases with increasing tidal elevation, resulting in a reduced time. The landward end of the slough has vast low-lying marshes and mud flats that are inundated during higher tidal elevations, causing the effective (average) wave depth to decrease with increasing tide elevation, which explains why the tidal wave phase speed decreases instead of increasing. The elevation-dependent reflective time caused by a time-varying wave phase speed modifies the shape of the seaward tidal wave relative to the shape of the shoreward tidal wave, which explains the evolution and distortion of a tidal wave in a reflective slough.