Field measurements from 1985 to 1990 and sequential aerial photography since 1945 show that overwash plays an extremely important role in the dynamics of Long Point, a large barrier spit on the north shore of Lake Erie. Overwash occurs primarily in the transgressive proximal and central zones of the spit, which together account for some 65 % of the total shoreline length of 41 km. During periods of high lake level, over 50% of the shoreline in these zones may be overwashed. Washover morphology ranges from continuous washover terraces in areas of low foredunes to isolated washovers with narrow throats and distinct fans where breaching has occurred through high dunes. Individual overwash events commonly produce deposits on the fan surface 0.25-0.75 m or more in thickness. Washover-fan sediments are dominated by nearly horizontal planar bedding, with deposits near the fan margins often having foreset bedding, reflecting deposition in standing water of the bay or of interdune ponds.The frequency of overwash occurrence is strongly influenced by long-term lake-level fluctuations, which produce a distinct cycle of overwash activity. During the high-water phase more than 40% of the shoreline may consist of active washover fans or inlet breaches. Even storms with a return frequency of 1-2 per year can lead to significant overwash activity, and the washovers are generally reactivated several times in a 2 or 3 year period around the peak water level. During the low-water phase wider beaches offer protection against even extreme storm events, resulting in washover healing and restoration of a continuous foredune.Les mesures sur le terrain effectuCes entre 1985 et 1990, et l'etude des photographies aCriennes ~Cquentielles prises depuis 1945, demontrent que le dCbordeme?t joue un r81e de premibre importance quant 2 la dynamique de Long Point, une barre CmergCe longeant la rive nord du lac Erik. Le debordement se manifeste principalement dans les zones de transgression proximales et centrales de la barre, qui combinCes representent environ 65% de la rive dont la longueur totale est de 41 km. Durant les periodes de haut niveau du lac, le dCbordement dans ces zones peut se produire sur plus de 50% de la rive. Les dep8ts de dkbordement forment, d'une part, des terrasses continues dans les aires basses des avant-dunes, et d'autre part, aux endroits oc 1'6rosion a perce les hautes dunes, des accumulations isoltes caractkrisees par des gorges Ctroites et des Cventails distincts. Les debordements individuels dtposent frkquemment une epaisseur de 0,25 a 0,75 m, ou plus, de sediments sur la surface des Cventails. Ces sediments de dCp8ts de dCbordement sur les eventails sont formCs principalement de couches planaires presque horizontales, et les dCp8ts IocalisCs prks des bordures des Cventails exhibent frkquemment un litage frontal oblique, refletant une sedimentation dans les eaux calmes de la baie ou des Ctangs entre les dunes.Les variations 2 long terme du niveau du lac influencent fortement la frequence des dkbordements et crCent un ...