Date of Award

12-2001

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Geological Sciences

Advisor

Joseph T. Kelley

Second Committee Member

Daniel F. Belknap

Third Committee Member

Duncan M. FitzGerald

Abstract

Sprague Neck Bar is a recurved barrier spit located in Machias Bay, Maine. Principle geomorphic features associated with Sprague Neck Bar include bedrock, coastal bluffs, till in grounding line (the Pond Ridge Moraine) and washboard moraines, mudflats, sand and gravel beaches, and a salt marsh. Sprague Neck Bar is attached to the western end of the Pond Ridge Moraine (Sprague Neck) and extends northward toward the head of Machias Bay for 845 meters before the system recurves to the southeast for 232 meters. The recurve system forms a broad tidal flat with evidence for northward and eastward migration of the spit. The main objectives of the project include: identification of major trends in shoreline change based on historic maps and aerial photographs, characterization of the main sedimentary environments of Sprague Neck, determination of the mechanisms influencing cross-shore and longshore transport, and finally an assessment of the relationship between relative sea-level rise and sediment availability and their role in barrier evolution was evaluated. Sprague Neck Bar is a mixed sand and gravel barrier spit. As with most mixed-sediment barriers the surface sediment fits a bimodal distribution, pebbles (-7 to -6 phi) and medium sand (0 to 1 phi). Surface sediment on the northward extension is not distributed in alongshore zones. The coarsest sediment is Tidal currents reach a greater maximum velocity, approximately 15 cm/s, along the recurve. Ebb and flood tidal currents are nearly equal in magnitude along the northward extension of Sprague Neck Bar and the recurve system. The qualitative historical analysis, c.a. 1776 to present, revealed no significant long-term change in orientation or morphology of Sprague Neck Bar. Sprague Neck Bar was examined in context of the stepwise-retreat model developed by Boyd et al. (1987), which is often applied to barrier systems in the Gulf of Maine. Sprague Neck Bar differs from the model by Boyd et al. (1987) in one aspect: Sprague Neck Bar does not have two discrete sediment sources and attachment points. The stepwise-retreat model explains barrier evolution in terms of two barrier spits, each attached to a local source deposit, separated by a tidal inlet. According to the Boyd et al. (1987) model, barrier evolution involves closure of the tidal inlet, spit breaching, and two new sediment sources. Therefore, Sprague Neck Bar is not an obvious example of the stepwise-retreat model.

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