Current and wave measurements in support of shallow water environmental modeling

In support of development and validation of a wave and current model for the coastal zone off Massachusetts in the United States of America, two deployments of a small tripod were made in 15 m depth in Buzzards Bay. The tripod bore an upward looking Acoustic Doppler Current Profiler (ADCP) and, on one deployment, a Modular Acoustic Velocity Sensor (MAVS) current meter 1.5 m above the bottom. From burst measurements acquired every two hours by these two instruments, a pattern of tidally and wind-driven flow with vertical shear was captured. Measurements of near-bottom current and wave orbital motion with MAVS extended the ADCP measurements from near the surface to the bottom region where interaction with the sediment is episodically important. In the September-October, 2008 deployment, the net flow north of Naushon Island was out of Buzzards Bay in alignment with the mean alongshore wind, which was mostly northeast (out of the bay) during this period. The water leaving the bay near Naushon Island must be made up somewhere else in the bay. Upwelling is also the dominate process north of Naushon Island, even when the winds measured at buoy BUZM3 at the SW opening of Buzzards Bay are near zero velocity. Waves are short period, typically broadband but with a peak near 5 seconds, fetch limited but still restricted to the along axis direction in Buzzards Bay. The longest fetch is in the ENE direction and the greatest wave event was from that direction with a significant wave height of 1.3 m and frequency of 0.2 Hz, from a 16 m/s NE wind. When conditions were calm, a consistent swell from the southwest of 22 cm significant wave height and 14 s period could be observed propagating in from the open Atlantic at the mouth of Buzzards Bay.