Bedform formation in the Glastonbury meanders of the Connecticut River

The Glastonbury meanders of the Connecticut River contain stable bedforms varying from less than 0.5 m to over 1.5 m in height, and 7 to 49 m in wavelength, dominated by medium-size sand. Field measurements, including the flow velocity and water depth were used to calculate stream power (in N/m2), and thus calculate the force needed to initiate sediment movement. Modeling experiments supported the field data. Our results show that, in these river meanders, bedform formation, morphology and stability are driven by stream power. Low Froude numbers (0.05-0.10) indicate that the river is usually in a state of equilibrium, but that it is punctuated by short intervals of bedform destruction during high discharge. Mean and median grain size were similar throughout the meanders and all parts of the bedforms suggesting the importance of hydraulic sorting. Field data included imaging the river using sidescan sonar, collecting sediment samples, measuring river discharge using an acoustic Doppler current profiler, and using USGS gage heights at Hartford and Middletown. Modeling was done with CCHE2D, a two-dimensional flow and sediment transport model developed at the National Center for Computational Hydroscience and Engineering.