11 Marine/Coastal Science (Posters)

CONSTRUCTION OF A BASELINE DATASET FOR SACO BAY SHOREFACE, SACO BAY, ME

Paper number: 11-4
Program: Technical Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

Begun in 1867, the paired jetty system at the mouth of the Saco River was intended to stabilize the river mouth tidal deltas to facilitate commercial navigation. The North Jetty was sequentially enlarged over 100 years to permit deeper draft vessels to enter the estuary and to create an anchorage at the site of the former tidal deltas. Presently 2032 m in length, the North Jetty is one of the largest along the US East Coast. Its enlargement was erroneously predicated on the belief that sand was moving into the estuary from beaches in the north, when in fact sand moves from the Saco River as a source toward the north. The North Jetty is believed by local property owners to cause erosion of the adjacent beach by reflecting waves onto the shoreline; 33 properties have been lost between 1968 and 1998. To remedy this, the Army COE is considering altering the North Jetty to increase sand retention on the beach at Camp Ellis. We are testing the hypothesis that the alteration will improve conditions on the beach by measuring river and nearshore sand movement pre- and post-alteration, and by evaluating shoreline and bathymetric changes following alteration.

We collected approximately 25 km2 of new multibeam bathymetry, 45 km2 of sidescan sonar imagery and 35 km of seismic reflection profiles of the shoreface immediately adjacent to the jetties during the summer of 2003. During this initial phase, we mapped a series of sediment bodies and erosional features including sand waves, bars, rippled scour depressions, and scour pits. These features were correlated with sediment textures, thicknesses, bathymetry, wave patterns, currents and proximity to the jetties. These new data were compared to sidescan sonar imagery acquired in 1995 for evidence of changes in sediment texture and evolution of rippled scour depressions. In general, the sediment texture patterns observed on the sidescan imagery show little change. General, large-scale bathymetric evolution of the region is under evaluation by comparison of time series bathymetry. A repeat survey of the area is planned for the summer of 2004, post nourishment and summer 2005.