Abstract:

The degree to which Hurricane Katrina altered baseline rates of erosion prior to the Deepwater Horizon (DWH) oil spill was determined through the quantification of erosion rate and fetch in northern Barataria Bay, Louisiana. Aerial images were used to classify marsh shorelines as a reference, moderately-oiled and heavily oiled. Three pre-spill time periods (1998-2004, prior to Hurricane Katrina; 2004-2005, during Katrina; 2005-2010, post-Katrina but pre-oil spill) and a post-spill period from 2010-2018 were examined. Twenty-one shoreline sampling stations, each ~30 m^2 in area, were established within an approximate 8 km-by-5 km area in Wilkinson Bay and Bay Jimmy in northern Barataria Bay, Louisiana, USA (between coordinates 29.44060°–29.47459°N, 89.88492°– 89.94647°W). This dataset contains triplicate estimates of the distance from measurement station to the marsh platform edge and estimates of the fetch, or over-water distance between measurement station and the nearest landmass.

Suggested Citation:

Deis, Don. 2020. Multiple point erosion values and fetch values at 21 stations in Barataria Bay, Louisiana, determined using aerial images from 1998-01-23 to 2018-08-12. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/PTHBYEJ0

Purpose:

The determination of the degree to which Hurricane Katrina altered baseline rates of erosion prior to the DWH spill. Erosion rate and fetch were quantified from aerial images of northern Barataria Bay, Louisiana, marsh shorelines classified as reference, moderately-oiled, and heavily-oiled over three pre-spill time periods (1998-2004, prior to Hurricane Katrina; 2004-2005, during Katrina; 2005-2010, post-Katrina but pre-oil spill) and a post-spill period from 2010-2018.

Data Parameters and Units:

The dataset consists of two spreadsheets. The file "LSU Sampling Stations Coordinates.xlsx" includes LSU Sampling Station [3-digit alphanumeric code], Station latitude [decimal degrees], and Station longitude [decimal degrees]. The file "Multiple Point Erosion analysis data fetch data.xlsx" consists of three worksheets, and includes the following: The worksheet ‘Multi-point analysis new’ contains Site_Name [AA#], Replicates [enum], Av_Dis_1998 [m], Av_Dis_2004 [m], Av_Dis_2005 [m], Av_Dis_Spring_2010 [m], Av_Dis_Fall_2011 [m], Av_Dis_Fall_2012 [m], Av_Dis_Fall_2013 [m], Av_Dis_Fall_2018 [m] The worksheet ‘Fetch data’ contains station designation [AA#], Pre-Katrina (1/1/2004, [km]), Katrina (10/2005, [km]), pre-spill (Spring 2010, [km]), and post-spill (Fall 2013, [km]). The worksheet ‘Aerial Names and Dates’ contains Aerial Name [season YYYY], Dates Flown (nominal, date and/or date range, [MM/DD/YYYY]).

Methods:

Aerial photographs captured between 1998 through 2018 were examined in order to quantify marsh erosion rates. Spatial analysis of photographic data was conducted using ESRI ArcMap 10.3.1 tools. Georeferenced aerial images from January 1998, January 2004, and October 2005 were used to examine pre-DWH marsh erosion rates and were obtained through the Louisiana ATLAS website (downloaded in October 2013 from the Statewide Louisiana GIS Database, http://lagic.lsu.edu/lgiscweb/view_download_data.asp). These images were digital orthophoto quarter quadrangle (DOQQ) color infrared imagery at 1-meter resolution. Post-spill geo-referenced aerial images from 2010 onward were made available by BP (British Petroleum Exploration and Production) through a cooperative agreement with the DWH Trustees (https://www.gulfspillrestoration.noaa.gov/cotrustees). Images from spring 2010 (near the time of the DWH spill but before landfall onto marshes in Bay Jimmy) and after oiling in the fall of 2010, 2011, 2012, 2013, and 2018 were analyzed. Sampling station positions using latitude/longitude were digitized into shapefiles; station locations were fixed in space and used for all subsequent erosion measurements. A scale of 1:500 was used for the measurement because this scale clearly showed marsh platform edges for all stations without pixilation. This resolution allowed the identification of the marsh edge at all stations even though reference and moderately-oiled stations had vegetation reaching to the edge of the marsh platform, while heavily-oiled stations had a bare marsh edge that bordered the water. Louisiana marshes are microtidal, allowing the marsh edge to be seen in aerial images, often even at higher tides. The distance from each station to the marsh platform edge was measured with an approximate accuracy of ±1 m (the width of a single-pixel) using the linear measurement tool in ArcMap; additional measurements to the marsh edge were taken from two sites located approximately 10 m on either side of the designated station, creating 3-subsample measurement points. Fetch was calculated as the sum of the distance from the station to the nearest landmass in each of the eight major compass directions (N, NE, E, SE, S, SW, W, and NW).

Provenance and Historical References:

Deis, D. R., Mendelssohn, I. A., Fleeger, J. W., Bourgoin, S. M., & Lin, Q. (2019). Legacy effects of Hurricane Katrina influenced marsh shoreline erosion following the Deepwater Horizon oil spill. Science of The Total Environment, 672, 456–467. doi:10.1016/j.scitotenv.2019.04.023

Individual Files: