ShoreZone Verification in Preparation for Marine Oil Spills

Unconsolidated segments of shoreline, including sand, pebble and boulder beaches, increase marine biodiversity by providing habitat variation in intertidal and subtidal environments. Small pocket beaches are of particular ecological importance, especially in bedrock-dominated fjord environments, as they provide hydrodynamic refuge and high quality feeding grounds for juvenile fish, including salmon. These areas, however, are also particularly sensitive to marine
oil spills, as the interstitial spaces between the sediment particles can trap oils and allow for resuspension on subsequent tides. Unconsolidated beaches also cause complications for marine response teams, as contaminated sediments must often be completely removed. Accurate knowledge of both the location and area of sensitive beach habitats is therefore critical, particularly in areas of heavy tanker traffic.

We collected ground-truth GPS points at all segments of unconsolidated shoreline for six islands in the Douglas Channel, British Columbia, to quantify the accuracy of ShoreZone, an available and widely used shoreline database. We
found that, due largely to its coarse spatial resolution, ShoreZone greatly overestimates the total amount of  unconsolidated beach on these islands, and fails to identify important pocket beaches. Further, the ShoreZone database does not provide reasonable estimates of beach area. We explored other possible methods to develop accurate physical shoreline data for the British Columbia coastline, including the use of terrestrial laser scanning data and satellite and aerial imagery. Our results highlight the need for improvements in physical shoreline classification, and the importance of accuracy assessments of large datasets.