Abstract:
Waterproof cameras were set on a two-hour time-lapse interval to photograph shoreline erosion for a coastal Louisiana marsh to document edge erosion over one year (August 2014 to September 2015). Image processing software was used to measure the width of the micro-headlands and micro-bay in select photographs. This data submission contains daily pictures of marsh erosion at one site in Bastian Bay, La and data on marsh erosion calculated from select images. Cameras were placed at two semi random sites, but only data from Site 2 was used to measure erosion because video from Site 1 was not usable for that purpose and could only be used in a qualitative sense. This dataset supports the publication: McClenachan, G., and R.E. Turner. 2017. Documenting marsh shoreline erosion: The land loss legacy effects of disturbances. Plos One. In revision.
Suggested Citation:
Turner, R. Eugene. 2018. Images and marsh erosion data from Bastian Bay August 2014 to September 2015. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7P55KXC
Data Parameters and Units:
File: R4.x264.000-0057_Marsh_Erosion_sub1.xlsx Worksheet: Camera - Uneven site Pic #: Video still image used for headland measurement data. Note that the filename for each picture number is formatted “GOPRO*.jpg”, where “*” is the Pic#. File Folder Containing Pic: File folder in GRIIDC “R4.x264.000-0057_Marsh Images” where the video still image is located (located by Pic#). Site: User defined site name where the camera was deployed. Date of picture: Date picture was taken (MM/DD/YYYY) Width of right headland (cm): Width of the right headland in centimeters, as measured using the ImageJ software. Width of micro-bay (cm): Width of the microbay in centimeters, as measured using the ImageJ software. Width of left headland (cm): Width of the left headland in centimeters, as measured using the ImageJ software. Notes Worksheet: Long term data Raw data for Table 1 in McClenachan & Turner 2017. Aromatics data for November 2010 and elevation change data is provided through August 2014 as background information on the study sites Note: Aromatics data is a one time soil sample at each site for date stated; Total Erosion data is the total amount of erosion at each site over the stated time period; Avg Soil Strength calculated with an n=4 for each; Avg Overhang calculated with an n=10 for each; Avg Elevation change calculated with an n=5 for each. Camera location, Corresponding long term site, Aromatics (ug kg-1) - Nov 2010, Erosion (cm) - Nov 2010-Feb 2011, Erosion (cm) - Feb 2011 - July 2011, Erosion (cm) - July 2011-Oct 2011, Erosion (cm) - Oct 2011-May 2012, Erosion (cm) - May 2012 - Aug 2012, Erosion (cm) - Aug 2012 - Sept 2012, Erosion (cm) - Sept 2012 - June 2013, Erosion (cm) - June 2013 - Feb 2014, Erosion (cm) - Feb 2014-Aug 2014, Erosion (cm) - Aug 2014 - Feb 2015, Overhang (cm) - Nov 2010, Overhang (cm) - July 2011, Overhang (cm) - Oct 2011, Overhang (cm) - May 2012, Overhang (cm) - August 2012, Overhang (cm) - Sept 2012, Overhang (cm) - June 2013, Overhang (cm) - Feb 2014, Overhang (cm) - Aug 2014, Overhang (cm) - Feb 2015, Shear Vane (kPa) - Avg 0-50 cm depth - Nov 2010, Shear Vane (kPa) - Avg 0-50 cm depth - July 2011, Shear Vane (kPa) - Avg 0-50 cm depth - Aug 2012, Shear Vane (kPa) - Avg 0-50 cm depth - June 2013, Elevation change (cm) - Nov 2010, Elevation change (cm) - May 2012, Elevation change (cm) - June 2013, Elevation change (cm) - Feb 2014, Elevation change (cm) - Aug 2014 File: R4.x264.000-0057_Marsh Images Windows folder containing images taken at Site 2. Images are organized in 9 Windows folders named according to time interval deployed ("Site2_MM-DD-YY_MM-DD-YY"). Data associated with some images are in R4.x264.000-0057_Marsh_Erosion_sub1.xlsx, by using the "Date of picture" and "Pic #" variables. Sites are as follows: Site 1-Even Site: 29.476367, -89.841933 Site 2-Uneven Site: 29.474283, -89.83445
Methods:
Field methods: Waterproof cameras were set on a two-hour time-lapse interval to photograph shoreline erosion for a coastal Louisiana marsh to document edge erosion over one year. The custom-designed camera outfits were placed in two locations that were 1 km apart along the northern shoreline edge of Bay Batiste in southeastern Louisiana. There was one camera at each location which was where shoreline erosion measurements were made by McClenachan et al (2013; Fig 1). The photographic records were taken from a public water body and monitored the 1st few meters of private land. The owner of the land, ConocoPhillips, issued access permit P0987 that gave permission to conduct the study at this site. Go-Pro© cameras were fitted with intervalometers to control the time intervals between photographs. We used a waterproof housing that included a battery pack and flash capabilities. One camera faced an even shoreline edge (a smooth shoreline with no micro-headlands), while the other faced an uneven edge (an undulating shoreline with at least one micro-headland; in this case, two micro-headlands surrounding one micro-bay) (Fig 2). Micro-bays are small indentations along the marsh shoreline, whereas micro-headlands are small protrusions along the shoreline; a micro-bay generally indicates there are two micro-headlands surrounding the micro-bay. Both cameras faced the marsh edge in a permanent housing located 1.5 m from the edge of the vegetation on the shoreline. A 2 m metal pole pushed 1.5 m into the sediments stabilized the housing to minimize camera movement during high water events. Three PVC poles were placed laterally along the marsh edge and in view of the camera to create a reference for measurements in each image. Each pole was 1.5 m apart from the next closest pole (Fig 3). This placement allowed for the calibration in each set of photographs, even if the cameras were not replaced in the housing at exactly the same angle each time the camera was changed. A PVC pole was placed into the marsh, behind the middle pole on the edge to measure the seaward-to-landward erosion in the field. The cameras were replaced approximately every six weeks, just before the batteries discharged completely. We calculated an erosion rate by measuring the width of the micro-headlands and micro-bay in the field, as well as the distance from each of the three poles to the marsh edge. These measurements provided us with a semi-frequent (every 1.5 months) field-measurements of erosion to compare to the width (lateral) erosion calculated using the camera images. The field-measured erosion was collected in the same method as in McClenachan et al 2013, allowing for a comparison of the two sites to the 30 other sites located across the same shoreline. Image analysis We used ImageJ (Ver. 1.48V) to measure the width of the micro-headlands and micro-bay in the photographs. The known distance between the poles calibrated the measurements for each sequence of photographs. This approach allowed for comparisons between picture sets, even if the camera were placed in the housing at a slightly different angle each time. An erosion event was qualitatively established from measurements of multiple photographs to be a change greater than ~2 cm. Not every image could be measured in ImageJ because of a variety of factors, including water level (sometimes water was over the camera), cloudiness on the camera lens, darkness, and algal growth on camera lens. Erosion was measured from one picture at the beginning and end of each week and, if there was lateral erosion, the erosion was then measured for each day until we determined which day/days the erosion occurred. Erosion was measured each time at the root line to minimize changes associated with where the measurement was taken. Sometimes this led to a “growth” of the headland as a piece began to erode and hung off the edge, until it eventually fell off completely. We were only able to measure the width (or lateral) erosion events using the ImageJ software. Erosion from the marsh edge inland was measured in the field using the position of the PVC poles. The data located in "Camera - Uneven site" are measurements from the images taken by the GoPro cameras. The widths (cm) of the microbay and right and left headlands were measured in the associated picture using the ImageJ software. The data located in "Long term data" include data that has been collected from permenant sites established for the McClenachan et al 2013 paper that correspond to the two camera sites. Data were collected for various projects between 2010-2015.
Provenance and Historical References:
McClenachan, G., R.E. Turner, and A.W. Tweel. 2013. Effects of oil on the rate and trajectory of Louisiana marsh shoreline erosion. Environmental Research Letters. 8(4): 044030.
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