Characterization of the vertical structure of tidal currents in the Golden Gate (San Francisco) inlet

Abstract

In the Golden Gate (San Francisco) inlet, tidal currents are dominant and have complex spatial and temporal variations owing to the large size of estuary connected through a narrow channel and the shallow ebb shoal (bar) at the mouth. To capture such variations, shipboard ADCP profiling is a technically viable approach that can yield unique insight into the vertical structure of currents. Shipboard ADCP data from four cruises conducted by the R/V Point Sur in the San Francisco Bight are used in the study. Transects along the channel axis were automatically extracted from the irregularly sampled underway data using changes in speed and heading in combination with geographic criteria. Processed data contains transects traversed in various tidal conditions. Flood currents are bottom intensified with more strength in the relatively deeper area of the channel. In low tidal range conditions, the directions and speed of surface currents are nearly uniform along the entire channel. Ebb currents are surface intensified, decreasing from the Golden Gate to the bar. In low tidal range, near-surface and bottom currents flow in opposite directions. The tidal currents exhibit cross channel variations in strength. Ebb results in surface outflow mainly along the northern part of entrance, whereas the flood flow is strongest along the southern part.