Investigating water movements around a shallow shipwreck in Big Tub Harbour of Lake Huron: Implications for managing and preserving underwater shipwrecks

by Bryan Flood, Lakshika Girihagama, Mathew G. Wells, Reza Valipour, Patricia Semcesen, Scott Parker

The Sweepstakes, in Fathom Five National Marine Park, is Ontario’s most iconic shipwreck with over 100,000 visitors each summer. Continued exposure to water currents has directly and indirectly affected the integrity of the wreck and resulted in management interventions including efforts to stabilize the wreck and control vessel activity (both duration and speed). Despite these efforts, a scour ring is present in the sediment around the Sweepstakes, raising concerns regarding the prolonged stability of the wreck. An extensive series of field measurements were made during the summer of 2015 with the aim of differentiating between natural hydrological processes present at this site and human-derived water movements during the summer visitor season. There is a high-degree of natural current variability from processes as diverse as wind-induced surface gravity waves, internal gravity waves, and diurnal flows due to differential heating. Our results show that summer circulation driven by internal gravity waves derived from upwelling, surface waves, and differential heating was insignificant with respect to sediment resuspension and thus unlikely to produce the observed scour around the shipwreck. Scour is most likely caused by energetic winter storms, which should be a focus of future studies. While vessel induced currents were detectable at the shipwreck, they were no larger than the normal summer hydrodynamic variability, thus suggesting that management efforts continue to protect the site generally.