QUANTIFYING TURBIDITY IN THE NEARSHORE OCEAN

Abstract

Naval mine countermeasure operations in the littorals depend on water visibility; however, turbid behavior in nearshore environments is largely unknown. This study investigates turbidity in the nearshore/lagoon environment to the 15 m isobath, in relation to hydrodynamic regimes of the Pajaro River estuary in Monterey Bay, California. Observations were made on how turbidity changes through a tidal river into the open ocean, over space and time, and whether the drivers are tides, waves, precipitation, or river discharge. Pairs of turbidity sensors at the top and bottom of the water column gathered data at various sites, along with salinity, temperature, pressure, and current. Data were collected from the October dry season continuously through April into the rainy season. Pajaro River discharge, local wave conditions, and tides were compared with observed turbidity. Findings indicate that the river regime is the dominant forcing mechanism. Shifts in turbidity behavior were also noted as rainfall increased. Tidal impacts were determined to be minimal; however, some indications suggest infragravity wave energy infiltration into the lagoon on flood tides may modulate turbidity signals. The U.S. Navy currently does not measure or forecast turbidity, and this study supports the need for such capabilities. Further study is needed to confirm results and determine definitive drivers of turbidity.Distribution Statement A. Approved for public release: Distribution is unlimited.Ensign, United States Nav