Influences of tidal and subtidal currents on salinity and suspended-sediment concentration in the Delaware Estuary

The relationships between tidal and subtidal currents and the temporal and spatial distribution of salinity and suspended-sediment concentration (SSC) in estuaries are problems of long standing. To identify these relationships in the Delaware Estuary, in 2005, instruments measuring current, salinity and SSC were deployed for three months. The survey captured a freshet event in April during which the freshwater discharge exceeded base flow by a factor of ten. Based on this data set and other available data such as river discharge of the estuary tributaries and winds, this thesis examines the major features of current, salinity and SSC in the Delaware Estuary over tidal and subtidal time scales.; The separation of the total current into tidal and subtidal currents indicates that the tidal current accounts for most (about 99%) of the variance in current speed and direction. Harmonic analysis indicates that the M2 tide is the dominating constituent in the Delaware Estuary. For a given station, the tidal current shows spring-neap variation, flood-ebb asymmetry and diurnal inequality. The tidal current also shows significant variability with depth and position along the estuary. The subtidal current is caused by river discharge, wind and tidal rectification. The mean current at the most downstream channel station is dominated by a two-layer circulation pattern, while the mean currents at the other two channel stations further upstream show essentially downstream flow from bottom to surface. The wind-driven current shows a complicated pattern associated with a combination of the remote and local wind effect. Tidal rectification contributes to the fortnightly current variability, but it is difficult to quantify its effect based on the available data.; The salinity is divided into tidal salinity and subtidal salinity. In contrast to current, the variance of the subtidal salinity accounts for the majority (more than 60%) of the variance of the salinity. For the tidal salinity, it varies roughly in quadrature phase with the tidal current, which indicates that tidal advection is the major factor in controlling the intratidal salinity variability. The subtidal salinity at the three channel stations correlates closely with the river discharge. The salt transport over the subtidal time scale is dominated by the advection of salt associated with the subtidal current, with the tidal pumping effect playing a secondary role.; SSC at the three channel stations varies significantly at daily and fortnightly time scales, roughly following the change in the magnitude of the tidal current over the tidal cycle and over the spring-neap modulation cycle. The large freshet event in April 2005 increased SSC at the three stations dramatically. At the three channel stations, the advective flux of suspended sediment is the major component of the total subtidal suspended-sediment flux observed during the study period. The depth-integrated suspended-sediment flux per unit width indicates that there was a net influx of suspended sediment between the two observational transects Bombay Hook and Blackbird Creek during the study period. This flux suggests that the landward component of the estuarine gravitational circulation is an important mechanism of sediment transport in the Delaware Estuary.