CHANGES IN THE SEDIMENT DISTRIBUTION OF A JETTIED CHANNEL AND BACKBARRIER SYSTEM AS A RESULT OF DREDGING, WELLS HARBOR, ME

Wells Inlet, located along the southern coast of Maine, has been the site of periodic dredging since jetties were constructed there in the mid-1960's. Most recently, the U.S. Army Corps of Engineers (USACE) completed dredging of the channel in late Nov 2000. Pre and post-dredge shoaling, wave regime, and general sediment distribution patterns have been studied using 19 laser survey profiles (Dec 1998, Mar 2000, Fall 2000, and Fall 2001), examination of wave height and current velocity data obtained from five 2-week long Acoustic Current Meter deployments (Jan 2000, Mar 2000, Fall 2000, and Fall 2001), and 500 sediment samples (Fall 2000, and Fall 2001). Additionally, detailed bathymetric surveys of the dredged channel were completed by the USACE for both pre and post-dredge conditions. The jettied portion of the channel is partitioned into the thalweg region containing sediment ranging from cobbles (10 - 40 cm) to medium sand and adjacent shallow areas composed of coarse to fine sands. This segregation has become more pronounced since the deepening of the navigation channel. The channel is backed by an extensive marsh system consisting of sand flats, mud flats, and isolated sandy patches of cobbles. The creation of a deep, wide, steep sided navigation channel in the southern portion of the inlet has led to reduced flood current velocities in the backbarrier. The reduced current velocities have resulted in the deposition of finer material along the northern and western tidal flats. Mean grain sizes for post-dredge samples are as much as 0.50-0.75 mm finer then those for comparable pre-dredge samples. Mutually evasive domains of ebb and flood tidal currents continue to dominate the jettied channel with average ebb current velocities in the thalweg exceeding flood velocities and average flood current velocities in adjacent shallow portions of the channel exceeding ebb velocities. Simultaneous wave height and current velocity measurements in the channel show that there is no change in the magnitude of wave/current interaction following dredging. Passing wave crests enhance flood velocities and retard ebb velocities by 10 - 25 cm/sec. Passing troughs have little or no effect on the current regime (0 - 5 cm/sec). Larger magnitude wave events observed in Nov 2001 show instantaneous current velocity reversals in the northern portion of the channel.