ASSESSING MORPHODYNAMICS AND SEDIMENT FLUXES ASSOCIATED WITH THE SACO RIVER, IN SOUTHERN SACO BAY, ME

Saco Bay features Maine’s largest sand beach system. The Saco River is recognized as a major source of sediment for the Saco Bay beach system, providing an estimated 10,000-16,000m³ of sand per year. The net direction of sand movement is to the north where riverine sediment has historically provided materials for barrier spit-growth. The 1867 construction of a jetty on the north side of the inlet has altered the Saco River’s ability to deliver sediment to the bay and changed the rate and patterns of sand movement throughout the bay. The jetty system now channels the Saco River 2032 m out to sea and the river mouth must be dredged every 10 years. Beaches adjacent to the northern jetty have eroded severely in the past century, with neighboring Camp Ellis suffering the loss of 33 properties since 1968. Previous estimates of river sediment output were based on limited measurements of upstream sediment discharge and the shoaling rate of the Camp Ellis anchorage at the river mouth. We want to better constrain the rate of sand introduction to the system from the Saco River by correlating the morphodynamics, stratigraphy and sediment transport of the system.

During the summers of 2003 we collected 25 km² of multibeam bathymetry, 45 km² of sidescan sonar imagery and 35 km of seismic reflection profiles of the river bed and shoreface immediately adjacent to the jetties. Repeat sidescan sonar and seismic surveys were carried out in 2004. With these data we mapped a series of sediment deposits and erosional features including sand waves, bars, rippled scour depressions, and scour pits. Features were correlated with ebb-flood orientation, sediment textures, thicknesses, bathymetry, wave patterns, currents and proximity to the jetties. Stratigraphy is constrained by two series of vibracores taken in 2002 and 2004. Additionally we launched a seabed drifter survey which after 5 months has a 25% recovery rate. The drifter data were correlated with meteorological conditions and previous hydrographic studies. Plans are in place for another seabed drifter deployment, and additional hydrographic work for Spring of 2005.