A TRANSGRESSIVE EVOLUTIONARY MODEL AND THE APPLICABILITY TO NEW ENGLAND BEACHES

Sprague Neck Bar is a 1.203 kilometer mixed sand and gravel, drift-aligned, recurved barrier spit attached to the western end of the Pond Ridge Moraine in eastern Maine. This system extends in a northeast direction in central Machias Bay. An initial hypothesis for the evolution of Sprague Neck Bar was the stepwise retreat model (Boyd et al., 1987) proposed for southern Nova Scotia, and often applied to New England beaches. This model requires discrete sediment sources (drumlins, moraines) and headland anchor points. As the sources are depleted during rising sea level, the system migrates landward episodically. The hypothesis placed Sprague Neck Bar in the barrier genesis and progradation stage, with the eroding Pond Ridge Moraine as the main source and anchor point. Examination of Sprague Neck Bar involved Total Station surveying, ground penetrating radar, current meters, sediment sampling, and analysis of historical charts and aerial photographs. Sprague Neck Bar apparently derives sediment from many, small washboard moraines oriented perpendicular to the barrier spit, not directly from the Pond Ridge Moraine. Dominant wind and wave directions are from the northwest and southwest. Sediment is carried by longshore transport to the north from the Pond Ridge Moraine. Wave refraction around the northern tip results in longshore drift on the recurves to the southeast and south. The recurve system forms a broad flat with evidence for northward and eastward spit growth. The southern portion of the spit is narrow and has experienced overwash. Comparison of maps and aerial photographs shows little change since 1776, indicating Sprague Neck Bar is a stable system in a phase of self-regulation that has not changed within historic times. Thus, Sprague Neck Bar is not a clear example of the stepwise-retreat model.