Geological Association of Canada, Newfoundland and Labrador Section Abstracts: Technical Meeting 2020

The primary aim of this study is to determine the sub-surface structure of coastal roads in three key areas prone to erosion in the town of Bay Bulls, Newfoundland and Labrador. Information about the subsurface can facilitate the development of long-term strategies to reduce coastal exposure to the effects of climate change. Three sites of potential concern for coastal erosion are on roads built on steep slopes. On the north side of the bay, at the Bread and Cheese site, the road faces the risk of being undercut by waves, whereas the Cliff site road has a wooden retaining wall which is starting to slump sideways. At the Quays, located on the south side of Bay Bulls, the road runs very close to narrow inlets within steep cliffs. Three geophysical techniques—ground-penetrating radar (GPR), direct current resistivity (DCR), and real-time kinematic (RTK) analysis — were utilized for this purpose, along with geological and coastal geomorphological observations. The GPR survey operates by sending a radar pulse down and recording reflections. The method revealed the extent of the fractured region at Bread and Cheese, the bedrock and rock structure interfaces on Quays road, and the location of bedrock and support beams at the Cliff site. DCR surveys measure the resistivity of the ground by sending an electric current into the ground. DCR identified the general structure of the ground, in terms of higher and lower resistivity blocks, which were then correlated with layers of stronger and weaker bedrock. In general, the Bay Bulls area is fortunate to be located in strong bedrock that is relatively resistant to wave action. Areas where the rock is fractured, or roads lie on Quaternary cover are most vulnerable to degradation.