Shoreline for the Isles Dernieres, 1887

The U.S. Geological Survey (USGS), in cooperation with the Coastal Research Laboratory in the Department of Geology and Geophysics at the University of New Orleans (UNO) and the Center for Coastal Energy and Environmental Resources at Louisiana State University (LSU), is investigating the processes of coastal erosion and wetland loss in Louisiana (Sallenger and others, 1987; Sallenger and Williams 1989; Penland and others, 1992).
Building on the USGS Louisiana Barrier Island Study (Williams and others, 1992) and the USGS Hurricane Andrew impact assessment (Penland and others, 1998), this data layer depicts the shoreline as it stood in 1887.
The Isles Dernieres are located about 120 km southwest of New Orleans. This barrier island shoreline is 32 km long and extends from Caillou Bayou east to Wine Island Pass. The Isles Dernieres represent a barrier island arc developed from the reworking and erosion of an abandoned distributary of the Lafourche delta complex within the Mississippi River delta plain (Penland and others, 1988). Previous work by McBride and others (1992) documented a long-term (1887-1988) gulfside erosion rate of -11.1 m/y and a short-term (1978-1988) gulfside erosion rate of -19.2 m/y. The long-term bayside (1906- 1988) erosion rate was measured at -0.6 m/y and the short-term (1978-1988) bayside erosion rate was measured at -5.2 m/y. The Isles Dernieres decreased in area at a rate of -28.2 ha/y between 1887 and 1988, suggesting the long-term date of disappearance would be 2015. The rate of area loss between 1978 and 1988 was measured at -42.7 ha/y suggesting a short-term disappearance date of 2004. In the 1992 Hurricane Andrew impact assessment by Penland and others (1998), the Isles Dernieres experienced a brief and intense period of increased erosion. The average gulfside erosion rate accelerated to -59.37 m/y and the average bayside erosion rate accelerated to -10.8 m/y during the year of the 1992 Hurricane Andrew impact. The Isles Dernieres rate of area change accelerated to -155.7 ha/y during the 1992 hurricane season. Hurricane Andrew accelerated the long-term area loss rate to -28.5 ha/y and the shortterm area loss rate to -49.54 ha/y. The Hurricane Andrew impact on the Isles Dernieres produced 3-5 years of erosion in a matter of days. After the Hurricane Andrew impact, the projected long-term disappearance date of the Isles Dernieres was reduced from 2015 to 2012 and the short term disappearance date was reduced from 2004 to 2003.
In this shoreline change update, the authors used the methods and transects used by McBride and others (1992) to insure data compatibility of the new measurements and analysis.