BEDFORM FORMATION IN THE GLASTONBURY MEANDERS OF THE CONNECTICUT RIVER

The Connecticut River flows from the Connecticut Lakes to Long Island Sound, traversing approximately 655 kilometers. In this study, bedload sediment transport through the Glastonbury meanders was analyzed. A Datasonics SIS-1000 sidescan sonar with sub-bottom profiler was used to map the bedform fields located between Rocky Hill and Hartford, Connecticut during periods of high and low discharge. During the spring survey of April 2010, discharge exceeded 880 m³/s, while during the summer survey of July 2010 discharge was less than 200 m³/s. Discharge measurements were obtained at various cross-sections throughout the Glastonbury meanders using a Teledyne RDI 1200-kHz acoustic Doppler current profiler (aDcp). Additional aDcp-ing was done in November 2010 to measure the flow velocity directly over six major bedform fields identified during the spring and summer surveys. The six bedform fields chosen to examine more closely contained sedimentary features ranging in size from less than 0.5 meters to nearly 2 meters in height, and had wavelengths ranging from less than 10 meters to over 40 meters. One hundred and forty sediment samples were gathered by experienced SCUBA divers from the six aforementioned regions. Grain size analysis completed using a laser diffraction particle size analyzer (LDPSA) revealed modal grain sizes ranging from 356 to 825 µm in the Glastonbury meanders. Using both the velocity, and grain size data bed shear stress calculations were made to determine the force exerted on the riverbed that initiates sediment mobilization, and the stream power (N/m² s) generated at various cross-sections. Our data was plotted in an equilibrium stability field diagram that correlated with sidescan sonar images taken in the field. CCHE2D software was also utilized to model sediment transport in the Glastonbury meanders over time in response to various flow regimes. Our data show that during the spring freshet, bedform fields became washed out, and were able to reform during the following months as flow velocities decreased. These sedimentary features serve as transient ecosystems for fish and plant-life, and the sediment they are comprised of may potentially transport contaminants.