ON THE HYDROGRAPHY OF THE ST. ANDREW BAY SYSTEM, FLORIDA1

The St. Andrew Bay System consists of four coastal plain estuaries of positive type. Temperature, salinity, and currents were observed over 24 hr for five to seven stations in the estuaries which were occupied five times in different seasons. At the two innermost stations, in the northern estuaries, the influence of drainage is strongest and the average salinity is low. There is almost no seasonal trend in average salinity or in the stratification of temperature and salinity. Tidal currents in the bays are predominantly diurnal, corresponding to tidal waves which enter the central bay through two passes. Surface currents often indicated longer duration of ebb than of flood stage, owing to the effect of drainage. Salinity change at the surface and bottom is caused primarily by the advective effect of currents, while in the mid‐depths, salinity change is mainly due to the vertical motion of the halocline. At some stations, surface salinity showed a trend of continual decrease during 24 hr, instead of a periodic change owing to persistent ebb currents. Bottom salinity, however, usually changed periodically or was almost constant, even at these stations. In one survey, surface salinity showed a trend of increase, owing to persistent flood currents caused by winds. Salinity change at a station in a narrow pass was most sensitive to change of currents. An equation which postulates that the change of salinity during one tidal period is proportional to mean horizontal gradient of salinity and mean current is tested by several examples. Vertical stability is largest at two innermost stations and shows no seasonal trend, as is often observed in other estuaries and in the open sea.