Penouille Spit, Evolution of a Complex Spit, Gaspe, Quebec, Canada

Abstract

Penouille Spit is a complex spit located on the north shore of Gaspe Bay in Quebec, Canada. Rates of deposition and erosion were derived from old maps and aerial photographs of beach ridges and shorelines on Penouille dating from 1765 to 1981. In July 1989, 41 beach ridges were mapped along 7 traverses and sediment samples were collected along 15 beach profiles. A 6-stage model of spit evolution was derived from the beach ridge and shoreline data. At Stage 1, an arcuate spit formed on a submerged deltaic platform near the mouth of the l'Eau River. During Stages 2 and 3, the Spit expanded westward about 2.1 km and rotated 20° in a counterclockwise direction. At Stage 4, erosion started at the west end of the Spit while deposition continued midway along the south shore. During Stage 5, a pair of recurved spits formed at the southeast corner of Penouille while erosion continued along West Beach. Finally by Stage 6, the south shore had rotated 40° and the corner spits converged enclosing a salt marsh at the southwest tip of the Spit. Rates of erosion along West Beach (0.50 ± 0.08 m/yr) and beach ridge accretion (45.5 ± 7.3 yrs/ridge) were used to estimate the net sediment flux (1,000 ± 160 m3/yr) and age of the Spit (2,110 ± 340 yBP). Wave refraction analysis provided evidence that Sandy Beach Spit on the south shore of Gaspe Bay blocked incoming storm waves and longshore currents, resulting in erosion along West Beach at 500 ± 80 yBP.