Subtask: Hurricane Impact and Wetland Loss in Coastal Louisiana

Subtask Leader: John Barras - USACE Vicksburg, MS

Aim

Identify episodic interior marsh loss caused by cumulative storm events over the past 60 years using a combination of satellite imagery and historical aerial photography. The information will provide estimates of extreme storm contribution to coastal land loss while refining the timing and magnitude of these events.

Approach

The objectives for this subtask are to:

1. Identify, quantify the individual and cumulative contributions and spatial distributions of hurricane-induced episodic impacts to land loss, where feasible, using both Landsat Thematic Mapper (TM) satellite imagery and historical aerial photography over the past 50 years in coastal Louisiana.
2. Collaborate in the development of a morphologic classification of of interior marsh loss caused by hurricanes based on observed loss patterns linked to known storm events identified using both aerial photography and satellite imagery.

Large-scale hurricane induced interior marsh loss estimated at 562 km2 was observed after landfalls of Hurricanes Katrina (Category 4) and Rita (Category 3) in 2005 (Barras, 2006). The estimated loss from both 2005 hurricanes accounted for 76% of the 743 km2 of loss occurring between 1978 and 2004 (Barras and others, 2008). The large-scale loss observed after the 2005 hurricanes implies that past extreme hurricanes, greater than Category 2 on the Safford-Simpson scale, may have contributed significantly to the 2,238 km2 of net loss that occurred within coastal Louisiana between 1956 and 1978. The 1978 to 2004 period, used for current land loss projections (Barras and others, 2003), was characterized by primarily low-intensity hurricane landfalls in Louisiana. The basic approach is to use event bracketing Landsat TM satellite imagery and historical aerial photography to identify potential areas of likely storm-induced land loss based on storm intensity, track, surge, and receiving basin morphology. Knowledge gained from prior studies expands existing extensive land-water area and trend information developed for Barras and others (2003), Morton and others (2005), Barras (2006) Barras (2007a), Barras (2007b), and Barras and others (2008) into a coherent framework for examining episodic related loss during the 1983 through present period using Landsat TM satellite imagery. The large number of Landsat TM scenes acquired since 1983 provides regional bracketing imagery suitable for rapidly identifying and assessing the permanence of extreme storm induced land loss over coastal Louisiana. The TM satellite's moderate spatial resolution is less than that of aerial photography but is adequate for identifying hurricane-induced loss exceeding a few acres in area (Barras, 2007a). The satellite's superior spectral resolution often aids in identifying surge-scoured and surge-flooded areas.

Examination of historical storm impacts, occurring prior to the advent of Landsat TM satellite imagery, requires obtaining available historical aerial photography to bracket known extreme storm events. The lack of contiguous coastal aerial photo coverage requires a vignette approach for identifying and quantifying historical storm-induced loss. Most available photography is panchromatic and was obtained at varying scales and coverage areas dependent on original flight mission requirements. Visual quality can range from excellent to poor, depending on film, print quality and age. Suitable event-bracketing photography may be available for portions of a historical storm's impact area but lacking over the entire impact area. The primary goals of this subtask are to link observed loss to known historical storms to provide a better understanding of loss contributions of extreme storm events. A secondary goal is to collaborate in developing a morphologic classification of extreme-storm induced loss. Initial observations of known storm-induced loss show that surge-induced loss patterns share similar characteristics over time, even features formed by events separated by decades.

Accomplishments

Primary accomplishments include visual identification and linkage of previously unidentified historical storm-induced interior wetland loss in coastal Louisiana to extreme storms that occurred during the 1956 to 1978 period. These include Hurricanes Audrey (1957), Carla (1961), Hilda (1964), Betsy (1965), Camille (1969), and Carmen (1974). Primary emphasis has now shifted to publishing these observations. Other accomplishments include the publication of Scientific Investigations Map 3019, _Land Area Change in Coastal Louisiana: A Multidecadal Perspective (from 1956 to 2006) and the publication of Scientific Investigations Map 3080, Land Area Change and Overview of Major Hurricane Impacts in Coastal Louisiana, 2004-08. SIM 3080 revises current coastal Louisiana land loss trends using linear regression based trend analyses for identifying current loss trends and for short-term land loss projections. SIM 3019 added a new fall 2008 land-water date to the information used in SIM 3080 to estimate the loss impacts of Hurricanes Gustav and Ike. Nearly instantaneous land loss from Hurricanes Katrina and Rita, Gustav. and Ike was equivalent to almost two and a half decades of prior coastal land loss from 1978 through 2004 implying that major hurricanes are a significant contributor to coastal land loss. The techniques used to identify hurricane-induced loss during the Landsat TM era were successfully used to identify historical storm-induced loss.

Publications

Manuscripts

Abstracts and Presentations

Other