|Titre||South Bay Ingohish and Black Brook Cove Beaches, Cape Breton Island, Nova Scotia|
|Auteur||Taylor, R B; Frobel, D|
|Source||Commission géologique du Canada, Dossier public 6268, 2009, 97 pages, https://doi.org/10.4095/248187 (Accès ouvert)|
|Éditeur||Ressources naturelles Canada|
|Media||en ligne; numérique|
|Lat/Long OENS||-60.5000 -60.1667 47.0000 46.5000|
|Sujets||plages; sables de plage; dépôts cotiers; profils de plage; milieu côtièr; études côtières; érosion côtière; courants littoraux; milieu littoral; littoraux; variations du littoral; sédimentologie; Nature
|Illustrations||location maps; graphs; photographs; aerial photographs; tables|
|Programme||Renforcement de la résilience des communautés canadiennes face aux changements climatiques, Géosciences de changements climatiques|
|Diffusé||2009 11 16|
|Résumé||(disponible en anglais seulement)|
Physical shoreline changes were monitored from1983 to 2008 along the head of South Bay Ingonish and Black Brook Cove, Nova Scotia. The objective was to define
typical rates of change for barrier and non-barrier beaches on northeast Cape Breton Island and to assess their recovery from human modifications during the 1970s. Thirteen visits to the area included six detailed surveys of Ingonish Beach and five
of Black Brook Cove. Both are coarse-grained beaches fringed by subtidal sand deposits which seasonally move on and off shore. Changes to the coarse component provided the best indication of longer term beach stability while changes in the sand
component provided the best indication of short term seasonal changes. An analysis of shoreline changes along the head of South Bay Ingonish was extended back to the 1930s by comparing georeferenced vertical air photos. To quantify short term
fluctuations in beach sand accumulation, additional surveys were completed by Parks Canada from May to October, between 1984 and 1992.
Small net changes in beach position and morphology imply Ingonish and Black Brook Cove beaches are in a
"dynamic equilibrium" with present wave conditions. Beaches in "dynamic equilibrium" can experience significant local changes during specific storms, but they can recover and restore their physical character as wave conditions change. Since 1936,
along Ingonish Beach net retreat at high tide was a maximum of 21 m (0.3m/a). Fluctuations in beach width caused by seasonal sand accumulation at both sites are commonly 10 to 20 m and as much as 36 m. Natural changes along the backshore of these two
beaches was minimal except where human modifications were made. Since 1983 the highest parts of both beaches retreated by less than 4 m however changes increased toward the ends of Ingonish Beach where crest elevations were lower. Waves are thought
to have overwashed the highest parts of the beaches in storms during 1983, 1991 and 2000. At Ingonish Beach it took roughly six to ten years for the beach crest to naturally repair itself after being cut into and lowered by waves. In contrast,
backshore areas excavated and lowered by human activity have not yet recovered after 26 years. Recovery is slow because the supply of coarse sediment is limited. Beaches must readjust their shape and redistribute their present sediment reserves to
adapt to larger changes across the backshore.
Shifts in the position and morphology of the nearshore bar complex has important implications for wave dynamics, the initiation of rip currents and physical changes along Ingonish Beach. A close
relationship was found between the spacing of cuts along the crest of Ingonish Beach and crescentic bar conditions offshore, but surveys were not frequent enough to define which wave and offshore bar conditions exist when the beach crest is cut and
rip currents develop. Future investigations of nearshore bar dynamics are encouraged. The information would improve human safety from rip currents and a better understanding of longshore shifts in beach stability. Ingonish Harbour Beach, which is a
low, coarse barrier separated by a tidal channel is not in equilibrium with present conditions. It was increasingly overwashed by waves after 1975 and was flattened during the late 1983 storm. Since 1936 the northern barrier has migrated 35 to 58 m
landward. Reinforcing its core with armour rock and rebuilding its crest to 4 m has halted its migration after 2004.
Physical indicators useful for measuring the seasonal and longer term state of coastal environments within Cape Breton Highlands
National Park are discussed and sweep profiles marking the highest and lowest fluctuations in beach sediment over 25 years provide a reference for assessing future changes on these and other similar beaches.