MODELING SEDIMENT TRANSPORT AND QUANTIFYING CHANNEL MORPHOLOGY OF THE SHEEPSCOT RIVER, COASTAL MAINE

We develop a sediment transport model for the Sheepscot River through the use of field measurements and remote-sensing techniques, in order to compare it with previous mapping of areas suitable for Atlantic salmon rearing and spawning habitat. The Sheepscot is a low-gradient, gravel bedded river with a slope of 0.1% to 1% and a median grain size of 1.1 to 8.5 cm at our six field study reaches. We calibrate a predictive model of bed material size that can be entrained under various flood discharges by measuring cross section profiles, vertical velocity profiles and bed grain size distributions at our six study sites, and monitoring bedload transport from July to December 2006 using marked particles at a subset of three reaches. After estimating the roughness coefficient, Shields parameter, basal shear stress, critical shear stress, and stream competence at each study reach, the model is extrapolated throughout the watershed based on channel slope and drainage area measurements derived from digital elevation model analysis. Shear stress is the most important factor in a sediment transport model because it sets sediment transport rates. We show that total basal shear stress calculations based on the Karman-Prandtl equation are about ½ the value calculated by the depth-slope product. The various methods to partition the total stress into its two components of form drag and skin friction may account for the difference seen in these two methods.