WAVE-INDUCED GRAVEL AND COBBLE TRANSPORT ON A CRENULATE SHORELINE OF A LARGE INLET, GRAYS HARBOR, WASHINGTON

Gravel and cobble transport is investigated on a mixed sand, gravel and cobble beach at the head of a crenulate shaped shoreline by magnetic particle tracer measurements and a phase resolving wave model validated with local wave and current measurements. Net alongshore transport of gravel and cobble is generally several times greater than the net cross-shore transport at Half Moon Bay in Grays Harbor, Washington. Particle transport is a complex function of grain size because of rejection and overpassing of mid- to largesize particles and hiding of smaller particles (Osborne, in press). Wave transformation to the inner bank beach was simulated with the locally verified, phase resolving Coastal Gravity WAVE (CGWAVE) model to determine relevant wave parameters near the break point. Measured gravel and cobble transport is found to be directly correlated with variations in alongshore energy flux with most of the variance in transport being accounted for by the variance in the breaker wave height, Hb. The relationship between the cobble transport and H b suggests the possibility of a threshold for alongshore transport at H b equal to approximately 0.3 m. Because these conditions are equaled or exceeded a high percentage of the time on the inner bank shoreline, a larger cobble size would be required to provide a stable inner bank shoreline position.