River Plume Tidal Effects / Flow Velocity Sedimentation Patterns

Understanding the dynamics of the tidal estuarine environment is an ongoing area of research. A Jetyak equipped with a downward mounted ADCP and transom-mounted single beam echosounder and CTD is in use by researchers in New Zealand to support ongoing studies of river plume migration processes that ultimately serve as an indicator of terrestrial pollution and nutrients content.

Repeat sampling of salinity, temperature and turbidity over the flood stage of the tidal cycle in the Firth of Thames was conducted to resolve tidal effects of the river plume and reveal sedimentation dispersal patterns. The Jetyak successfully captured data inside and outside the surface plume and revealed plume migration patterns as the flood stage of the tidal cycle progressed. The data collected will provide inputs to further model land runoff contamination and the effect of wind and waves on plume dynamics.

The Jetyak's ability to efficiently cover shallow areas and maintain repeatable transects between missions without prop fouling due to heavily vegetated bottoms will support further sediment deposition and erosion studies planned over longer temporal and wider spatial study areas.

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Estuary Drag Modeling

The drag force is an important component of estuarine momentum balance. It directly affects a number of complex processes, including tidal propagation, flooding potential, marsh inundation, estuarine exchange, mixing processes and salinity intrusion. Models to predict water level elevations and velocities in estuaries require drag parameters as an input. These vary with bottom friction caused by roughness, and also with the condition of vegetative bottom structures, topographic features and particularly sinuous channel planforms.

Bathymetric surveys of the North River estuary in eastern Massachusetts were conducted using a Jetyak equipped with a Ping DSP 3DSS bathymetric sidescan sonar and a NovAtel SPAN-IGM-A1. The bathymetric sonar was optimized for shallow water surveys, capable of measuring seafloor topography with resolution and accuracy of better than 10 cm in both horizontal and vertical, with swath widths of up to 10x water depth. The final bathymetric output was gridded in 50-cm bins for overall bathymetry of the mid-estuary region with selected areas gridded at 20 cm for detailed analysis of bedform geometry.

Following data collection and analysis, including direct observations in the study area which experiences a tidal range of approx. 3.5 m, drag coefficients were found to be between 3 to 7 times greater than the traditional coefficients normally used.

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