SEDIMENTARY PROCESSES AND THE EVOLUTION OF THE DISTAL BAYSIDE OF LONG-POINT, LAKE ERIE

Long Point spit, on the north shore of lake Erie, is >40 km long and p resently building into water that is >40 m deep. Annual sediment suppl y to the spit is estimated to be 1.0 x 10(6) m(3).a(-1) and is derived from the erosion of cohesive bluffs along more than 90 km of shorelin e to the west. The shoreline of the distal bayside consists of narrow barriers that connect the ends of dune ridges and enclose interdune po nds and swales. Unlike most barrier spits, the distal end shows little evidence of the formation of dune recurves, and the shoreline of the bayside, rather than fronting a protected bay, is exposed to waves gen erated by northeast winds blowing over a fetch > 100 km. Results of wa ve refraction analysis indicate that because of the great depth of wat er at the tip, there is almost no refraction of the dominant westerly and southwesterly waves around the distal end, thus inhibiting the for mation of recurves. Net sediment transport on the distal bayside is to wards the distal end of the spit. The result is the development of a n arrow spit platform extending the spit directly into the deepest part of Lake Erie. All sediment reaching the distal end along the exposed s outh shore is transported onto this platform and none reaches the dist al bayside. The negative sediment budget on the distal bayside results in transgression of the shoreline through truncation of the dune ridg es, and overwash and breaching of the small barriers. Historical aeria l photographs show that most of the overwash and breaching occurs duri ng periods of long-term high lake levels, with the barriers being rebu ilt landward of their former position during the following periods of lower lake levels. Progradation of the south shore at the distal end i s thus partly counterbalanced by the transgression of the bayside.