Cross-Shore Sediment Transport on a Naturally Barred Beach
NAVAL POSTGRADUATE SCHOOL MONTEREY CA
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Bailards sediment transport model 1981 is evaluated using field data obtained on a naturally barred beach. Principal field measurements consist of a cross-shore array of bi-directional current meters spanning the surf zone and daily bathymetic surveys. The model predicts bed and suspended Load transport separately based on various velocity moments. The velocities are partitioned into mean currents, long waves 0.05 Hz and short waves .0.05 Hz to determine their relative importance to the transport. Velocity moments are computed over 90 minutes intervals to resolve tidal fluctuations. Finally, predicted transport rates are integrated and compared with daily cross-shore bathymetric profiles Averaged over a 400m length of beach. Results indicate the suspended load was consistently greater than bed load as much as an order of magnitude during episodes of large incident waves, owing to the slow fall velocity 2cms of the fine grain sand within the surf zone. The contribution by the mean current, long and short waves to the cross-shore transport were of the same order. Variance of transport during all stages of tide and over a range of incident waves were consistently greater in the vicinity of the bar and trough than seaward of the bar and on the beach face. Tidal signatures were apparent in all modes of transport. The model appeared to under-predict measured bathymetry during low-energy periods and over-predict during high-energy conditions. However, the model does correctly predict the first order of movement of the bar.
- Physical and Dynamic Oceanography