EFFECTS OF A DREDGED NAVIGATION CHANNEL ON ADJECENT TIDAL FLATS AT WELLS INLET, WELLS, MAINE

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 November 2000. Pre-dredge shoaling and general sediment circulation patterns have been studied using 19 laser survey profiles (December 1998, March 2000, September 2000, and November 2000), 250 sediment samples (fall 2000), and examination of wave height and current velocity data obtained from three 2-week long Acoustic Current Meter (3DACM) deployments (January 2000, March 2000, and September 2000). After the dredge 19 laser surveys, 350 sediment samples, and three 2-week long 3DACM deployments were conducted during the spring and summer of 2001. Additionally, a detailed bathymetric survey of both the jettied channel and navigation channel were completed by the USACE. 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 navigation channel in the southern portion of the inlet has led to decreased flow in the northern portion of the channel. The weaker current velocities have resulted in the deposition of very fine grained material along the northern tidal flats. 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 by as much as 16-17 cm/sec and average flood current velocities in adjacent shallow portions of the channel exceeding ebb velocities by as much as 17-18 cm/sec. Simultaneous wave height and current velocity measurements in the jettied 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 (changes of 0 - 5 cm/sec).