Research Document - 2015/017

Remote sensing of the bathymetry and substrate of selected areas of Lake St. Clair - using the Remote Operated Vehicle for Environmental Research (ROVER) to detect dredging spoil piles near selected river mouths

By J. Gardner Costa, L. Wang, S.D. Mackey, and J.J.H. Ciborowski

Abstract

Lake margins are especially sensitive to coastal alteration by humans. Activities such as dredging have the potential to impact fish habitat. This is of special concern in Lake St. Clair, which is home to numerous species at risk including Northern Madtom, Eastern Sand Darter, and the Channel Darter. Yet, limited technology exists to survey shallow waters. We developed the remotely operated ROVER to collect high-resolution bathymetric data in shallow areas, such as undredged rivermouths. Our objectives were to assess substrate profiles and bathymetry in the navigation channels of Belle River, Pike Creek, Puce River, Ruscom River, Thames River, and Mitchell's Bay. Also, we surveyed 1 km2 zones adjacent to the rivermouths to determine whether spoil piles could be detected. The condition of navigation channels varied from site to site; whereas some channels had well maintained trenches, other sites were unnavigable by boat. We found little to no vegetation at any of the sites, suggesting these areas may not be suitable fish habitat. We were unable to conclusively identify spoil piles at any sites, suggesting that either;

1. dredgeate was not dumped in the specified location or,
2. spoil sites do not remain intact for very long and likely dissipate after the first major storm event.  

We also found that all proposed spoil sites were located at depths less than the prescribed 3 m boundary. This discrepancy was later clarified in that the 3-m limit was a maximum depth set by the local Conservation Authority and the Ministry of Natural Resources. Nevertheless, future studies and dredging activities should take water depth into account when choosing suitable spoil sites, and keep better records of the time and location of dredgeate dumping to help delineate spoil sites.  If future work is to be done, researchers and Management should work together to align surveys with dredging activities to provide baselines for what a ‘fresh’ dredgeate site looks like and for how long spoil piles persist.

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