Coastal Character and Coastal Barrier Evolution in the Bras d'Or Lakes, Nova Scotia

Abstract

Little coastal geological research has been conducted in the Bras d’Or Lakes. This is the first reexamination of the coastline since the early 1900s. The 1234 km of coastline is extremely varied in relief and morphology. In terms of composition, 13.5% of the shores are rock, 1.6% are artificial or human-made, and the remainder is composed of unconsolidated sediment. It is estimated that 27% of the shores are along narrow channels and embayments which are sheltered from higher wave energy, but many are low lying which makes them more vulnerable to increased flooding as sea level rises. Many of the larger coastal barriers noted in the late 19 th century remain. Using the oldest and most recent air photos and aerial video, changes at selected coastal barriers are assessed and a conceptual model for coastal barrier evolution is presented. Five natural phases of evolution were identified: (1) initiation, (2) growth, (3) establishment, (4) breakdown and (5) stranding or collapse. An alternative outcome for many barriers is artificial constraint (6), which is becoming more common as human activity increases in the Lakes. The criteria used in the model were applied to 80 of the largest coastal barriers to check its application as a guide for assessing shoreline stability. Thirty-nine percent of the barriers were identified in a building and established phase, and 44% in a breakdown to collapse phase. Field surveys are required to confirm the model and sample material for determining the age of coastal barriers and the duration of different phases of their evolution.