USGS Reports Latest Land-Water Changes for Southeastern

The USGS National Research Center 60-square miles projected to occur from a period of is reporting that a total of 118 square miles of land 50 years (2000-2050) by the Louisiana Coastal Area has been transformed to new water areas in a 9,742 Ecosystem Restoration Study. square mile area from the Chandeleur Islands to the The Breton Sound basin’s water area increased Atchafalaya River. This area encompasses the basins by 40.9 square miles; Terrebonne basin by 19.4 of Breton Sound, , Pearl River, square miles; Pontchartrain basin by 19.1 square Pontchartrain, Barataria, Terrebonne and the western miles; the Mississippi River basin by 17.8 square quarter of the Atchafalaya basin. miles; Barataria basin by 17.6 square miles; and This land-water change is from the fall of 2004 to the Pearl River basin by 4.4 square miles. The only the fall of 2005, after Hurricanes Katrina and Rita. area where land did not change to water was the These numbers are similar to ones reported to the task Atchafalaya basin. force of the Coastal Wetlands Planning, Protection New water bodies and expanded water bodies and Restoration Act in November by USGS, but they formed on the eastern side of the Mississippi River now also include land-water changes for the eastern basin; the northwestern portion of the Breton Sound quarter of the Pontchartrain basin, including the basin, from Delacroix to Caernarvon; the northern Chandeleur Islands. The data, acquired by analysis and eastern shorelines of Borgne; and along the of Landsat 5 Thematic Mapper (or TM) satellite north shore of from Mandeville to imagery, have also been further verified by additional the Mississippi border, including extensive impacts in satellite-image analysis, two small plane overflights, the Pearl River basin. limited field investigations, and peer review. Many of the new water areas consist of shallow The permanency, however, of the new water areas ponds where the marsh surface has been sheared may not be known for several growing seasons. Some or ripped to the root mat or to the underlying firm of the shallow areas may recover rapidly while others substrate of clay by storm surge. Littering some of may remain open ponds. For example, new green the sheared areas are marsh balls (rolled up marsh vegetation was observed in storm-impacted areas vegetation) and other debris, not large enough to over most of southeastern Louisiana during the small be identified by the satellite imagery used to detect plane overflights. land-water changes. The combined land-water changes caused by Other areas appear as large shallow ponds or Katrina and Rita exceeded all such changes in coastal with areas of exposed mud flats that vary in Louisiana from previous recent hurricanes combined size depending on water level. Groups of small such as Hurricanes Andrew (1992), Lili (2002) and interconnected ponds have been expanded in some Tropical Storm Isidore (2002), as identified with areas by the shearing of the intervening marsh. The Landsat satellite imagery. The change from land TM satellite may identify some of these shallow to water between the fall of 2004 and 2005 in the impact areas as either land or water, depending on Breton sound basin was equivalent to 60% of the total tidal and meteorological conditions when the image land-to-water change in the sound area between 1956 was taken. Multiple images over time along with and 2004. field investigations will be required to determine the Moreover, the change from land to water in all of permanency of new water areas. coastal Louisiana east of the Mississippi River from Areas of floating fresh marsh and some scrub-shrub 2004 to 2005 was 72.9 square miles, exceeding the were completely removed in the northern Pearl River

U.S. Department of the Interior U.S. Geological Survey February 2006 basin, while a series of shears was cut across the upper Breton basin and caused the formation of southern portion of the basin. limited new ponds and some expanded ponds from The fresh marsh in northwestern Breton Sound central Barataria basin across the Terrebonne basin basin was completely rearranged, displaying multiple to the Atchafalaya River. These impacts occurred shears that trended in a northwest-southeast direction. primarily in fresh and intermediate marshes, although Large deposits of wrack accumulated adjacent to or similar effects were observed in brackish marshes. on top of spoil banks and natural distributary channels Rita’s surge likely moved areas of floating fresh and often completely surrounded willows and shrubs. marsh in the western Terrebonne basin. Some areas Shallow mudflats, sometimes peppered by marsh of submerged and floating aquatic vegetation were balls and other debris, were present throughout the possibly removed or shifted by the surge. area. Over 90 percent of the new water area appearing To analyze land-water change, USGS scientists after the hurricanes in Breton Sound occurred within in Louisiana use remote-sensing technology and marshes that had been previously classified as fresh geographic information systems. For this analysis, and intermediate (that is, between fresh and brackish they compared land and water areas identified in in salinity). Landsat 5 Thematic Mapper imagery from several The more mineral-rich brackish and saline marshes dates in the fall for the years 2001, 2004 and 2005. appeared to have fared better, as indicated by the lack This imagery was used to successfully identify of large new water areas in central Breton Sound new water areas ranging from several acres to over basin and the Bayou Biloxi marsh. Fringing shoreline 1,000 acres as well as to identify areas of new land erosion and marsh scouring, as well as the formation consisting of rearranged marsh, wrack or storm- of small ponds, were observed in the brackish-saline deposited sediment. The imagery was collected marshes, while the greatest impacts occurred in the by the USGS National Center for Earth Resources more organic fresh and intermediate marshes of the Observation and Science in Sioux Falls, S.D. Mississippi River basin, upper Breton Sound basin In the future USGS scientists and partner agencies and Pearl River basin. will continue to study hurricane recovery, future land- Compression features (marshes compressed like an water changes and restoration of land in southeastern accordion or like pleats) of a mile or more long were Louisiana by using satellite imagery, high resolution observed in upper Breton Sound basin. Smaller but digital imagery acquired from aircraft, and field distinct compression features were also observed in investigations. The USGS will expand these efforts to the North Shore marsh. include southwestern Louisiana, which was affected Most areas west of the Mississippi River, with by Hurricane Rita. the exception of those east of Katrina’s landfall, were impacted more by Rita than Katrina. Areas of significant shoreline erosion, possibly caused by For more information: Katrina’s winds were, however, detected along the www.lacoast.gov or www.nwrc.usgs.gov southern shorelines of Lake Salvador and Little Lake John Barras 225-578-7486 in central Barataria basin. Rita’s surge rearranged James B. Johnston Katrina’s wrack (primarily marsh plant debris) in 337-266-8503