ABSTRACT: Ecosystem changes in the Annapolis Estuary: Causes and remediation of shoreline erosion at Fort Anne National Historic Site, Nova Scotia, Canada.

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Abstract

Because of the non-linearity of estuarine interactions, morphological changes often affect important physical processes with consequences that are extensive in both space and time. The full effects of human modifications (e.g. construction of dykes, causeways, etc.) are commonly not predicted because fundamental biophysical relationships are not understood sufficiently well. The Annapolis River and Estuary have been extensively changed since European settlement of the region in the early 17th century, through dyking, reclamation of marshes for agriculture, construction of dams, and a tidal power generating station. In 1991, timbers used to support a steep embankment at Fort Anned National Historic Site, Annapolis Royal, (Nova Scotia) became visible for the first time since they were laid in the 18th century. Erosion of this shoreline has continued during the last few years until very little remains of an extensive saltmarsh that formed the seaward boundary of the Fort and previously protected it against wave action. The principal change appears to have been construction of the Annapolis Causeway in 1960, although the the full effects were not appreciated for more than three decades. With disappearance of the marsh, wave action has been directed at the foot of the embankment, threatening the stability of the cribwork and the embankment that it supports. In March 1994 a 4 m section of the southwest ravelin slipped down below the high water level, leaving an exposed surface susceptible to erosion by waves at high water, and to precipitation at all times. In addition to wave action on the embankment itself, fine, red glacio-fluvial sediments that were previously capped by marine muds are re-suspended during every flood tide. Erosion of this red clay will probably continue as long as it is exposed to water, resulting in a steady increase in the slope of the beach, and increased vulnerability of the embankments of the Fort. This presentation will review research conducted since 1991 that is aimed at identifying the processes involved, and providing a comprehensive model of biophysical processes. The model is being used to plan long term remedial measures for the Fort shoreline that will protect one of the most important historic sites in Canada.

Bibliography of Canadian Geomorphology