Suspended Sand Transport along Pier Depression

Velocities and sand concentrations measured along 20 transects at the Field Research Facility (FRF) at Duck, North Carolina during October 16–23, 1997 are analyzed to examine the cross-shore and longshore suspended sand transport in the FRF pier depression. The suspended sand volume $V_s$ per unit bottom area remains large outside the surf zone in the depression. The depth-integrated offshore and longshore suspended sand transport rates are shown to be estimated as $a$ , $\overline{U}$ $V_s$ and $\overline{V}$ $V_s$ , respectively, where the empirical parameter $a$ is in the range of 0.1–0.4 in the depression, $\overline{U}$ is the cross-shore current and $\overline{V}$ is the longshore current. The offshore suspended sand transport rate at the end of the pier is estimated to be as large as $3.5{\text{m}}^3/\text{h}/\text{m}$ at the peak of a storm with an offshore significant wave height of 3.5 m. The sand transported offshore appears to have been supplied by the longshore sand transport toward the pier depression.