Date of Award

8-2006

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Oceanography

Advisor

Joseph T. Kelley

Second Committee Member

Daniel F. Belknap

Third Committee Member

Carol D. Janzen

Abstract

Saco Bay contains Maine’s largest sandy beach system. Sediment accumulation and erosion within Saco Bay are greatly influenced by a paired jetty system at the mouth of the Saco River. Initially constructed in 1867 by the United States Army Corps of Engineers (USACOE), the jetty system was intended to stabilize the river inlet and to facilitate commercial navigation. Now 2032m in length, the north jetty is one of the largest along the US East Coast. Its enlargement was erroneously predicated on the belief that the beach system was glacially sourced and sand was moving into the estuary from beaches in the north, when in fact sand moves from the Saco River as a source towards beaches in the north. As a result, the adjacent beach, Camp Ellis has undergone severe erosion suffering the loss of 33 properties since 1968, while the most distal beach north of the jetty has accumulated enough sediment to construct an additional 50 homes in the past 50 years. 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. To better constrain the conditions under which the Saco River contributes sand to Saco Bay a series of instruments deployed in April 2005 on three moorings inside and outside the Saco River jetty system collected current velocity, salinity and pressure data. These measurements characterized the high discharge event and its implications for transporting sand outside the jetty system. Discharge values from 125-175 m3s-1 were identified as the threshold envelope at which the Saco River transports sand in its bedload to Saco Bay. Put in an 89-year historical context, the Saco River contributes sand annually to the embayment but the amount may vary significantly year to year. Once sand exits the jetty system it may respond to seasonably variable shelf conditions, react to artifacts of the jetty system, or exit Saco Bay. Sedimentary pathways vary with season and location within Saco Bay. Mandated by Section 111 of the Rivers and Harbors Act, the USACOE continues to have an active role in Saco Bay. Currently the USACOE is awaiting approval of federal monies to construct modifications to the jetty system and deposit 76,455 m 3 of beach nourishment at Camp Ellis. The proposed modifications include two 120 m breakwaters and a 154 m-long jetty spur constructed upon the active shoreface. Scientific data indicate that sedimentary pathways are complicated and vary seasonally in Saco Bay and potential permanent structures may disrupt these avenues of sediment transport. Before action can take place in Camp Ellis a series of decisions concerning funding, intergovernmental partnerships and jurisdictions, and an Environmental Assessment must be completed.

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