QUANTIFYING RAPID EROSION IN COASTAL CONNECTICUT USING REMOTELY SENSED IMAGERY, GIS, AND DETAILED GROUND SURVEYS

Griswold Point is an east-west trending sand spit located in Old Lyme, Connecticut, USA, just east of the mouth of the Connecticut River in Long Island Sound. The spit is an important resource for wildlife and recreation, as well as an excellent location for studying coastal change and human influences. We have combined aerial photographs from the past 70 years, recent satellite images, GIS, and a one-year detailed ground survey to study long and short term changes along Griswold Point. Throughout its history, the spit has experienced long periods (~50-80 years) of relative stability punctuated by short periods of change that adjust its overall morphological configuration. Beginning in the winter of 1992/1993, Griswold Point entered a period of rapid erosion greater than any in its previous recorded history (~150 years). From 1934 to 1991, Griswold Point retreated northward an average of 85 m, lengthened by 140 m, lost an average of 40 m of width, and lost 30,000 m2 of area. The long term narrowing of the spit – potentially caused by decreased sediment supply and the inability of the system to recover after storm events – in conjunction with two large nor'easters within a three-month time span, breached the spit over the winter of 1992/1993. This breach imposed a barrier to longshore sediment transport, and the ensuing gradient in littoral drift caused the rapid erosion of the beach down-drift of the breach. The supply of sediment from the eroding spit, in combination with the diversion of river flow through new outlets, caused the western tip of the spit to extend at an accelerated pace and the established Blackhall River channel to close. Despite the relatively undeveloped nature of the Connecticut River estuary, Griswold Point is affected by both local and global human influences; the most prominent of these include the presence of groins and shoreline armoring within the system, and long term sea-level rise. Quantitatively describing the long term trends and recent changes to the spit are critical first steps to understanding how human development affects the dynamics of this system.