THE PATTERN AND PROCESS OF COASTAL BARRIER SYSTEM OUTLET CLOSURE EVALUATED USING GPR AT NORTH SANDY POND, EASTERN LAKE ONTARIO, NY

The eastern Lake Ontario sandy shoreline extends for about 26 km from the Salmon River in the south to Black Pond in the north.  The geomorphic environments include inland coast; ponds and wetlands; subaqueous barrier platforms; subaerial barriers with beaches and dunes; lake-side subaqueous shorefaces; and pond outlet channels. The term ‘outlet’ is preferred here to ‘inlet’ because in the absence of tides, the barrier breaches remain open due to the net water movement out of the ponds. The main sand source is reworked glacial shoreline sediment which now forms a sand sheet, up to a few meters thick, extending 5 to 10 km offshore, at depths of 30 to 45 m. Little sand is being added to the system, and both longshore and landward sediment transport converges on North Sandy Pond.

Eastern Lake Ontario provides unique habitat for a number of rare plant and animal species as well as facilitating recreational opportunities. North Sandy Pond is a long-term sediment sink and will eventually evolve from a lagoon into a wetland, similar to those further north. For the time being, the pond outlet facilitates access to the calm-water marinas and boat launches within the lagoon. However, the natural barrier and pond outlet is a constantly changing geomorphic system which maintains dynamic equilibrium between net sediment transport from the lake to the pond, and net water flow from the pond to the lake. The outlet location has changed five times in the last 140 years, and the development of conservation and recreation goals requires better understanding of these coastal processes.

This preliminary study has demonstrated that the eastern Lake Ontario coastal barrier system is conducive to investigation by ground penetrating radar and provides a rare opportunity to examine the pattern and process of outlet closure in a freshwater, non-tidal environment. Approximately 2.8 km of good quality beach-parallel data have been acquired up to about 7 m depth. Radar facies have been characterized along the entire barrier and former outlet locations have been identified. While interpretation of radar reflections indicates a significant contribution to barrier development from from aggradational processes perpendicular to the barrier long axis, both northward and southward prograding sedimentary sequences are associated with outlet closure.