Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Albert Y. Kuo


A two-year period of monthly slack water survey results suggest that in addition to the classical estuary turbidity maximum (ETM), a second peak of bottom total suspended sediments (TSS) concentration, or a secondary turbidity maximum (STM), often exists in the mid-York Estuary. This STM, detected from majority of the slack water surveys, moves back and forth in the region of about 20--40 km from the York River mouth. Moreover, the distribution of potential energy anomaly indicates that the STM may be related to the stratification patterns of the water column. A mathematical analysis suggests that four processes may be important to the formation of the STM: convergence of bottom residual flow, tidal asymmetry, inhibition of turbulence diffusion by stratification, and local erosion. An intensive survey was conducted in the middle part of the York River. None of the four mechanisms was in favor of convergent sediment transport in the examined region. Accordingly, the STM did not show up in the slack water survey conducted two days before the intensive survey. The intra-tidal variations of the bottom TSS concentration was shown to be proportional to bottom shear stress in most stations, which indicates that bottom resuspension is an important source of TSS in this region. The survey results also suggest that lateral sediment transport is not negligible in the study area. A three-dimensional numerical model was applied to the York River system. The model reproduced the basic features in both the salinity and TSS fields. Sensitivity model studies confirmed the existence of the STM under low and mean flow conditions. Analysis to the model results shows that bottom resuspension is an important source of TSS in both the ETM and the STM. The location of the ETM is well associated with the null point of bottom residual flow under various flow conditions. Convergent bottom residual flow, as well as tidal asymmetry, were shown to be the most important mechanisms that contribute to the formation of the STM. Model results suggest that the association between the STM and the stratification pattern is due to geometric features.



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