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Near-Continuous Monitoring of a Coastal Salt Marsh Margin: Implications to Predicting Marsh Edge Erosion
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  • Jack A. Cadigan,
  • Navid Jafari,
  • Nan Wang,
  • Qin Jim Chen,
  • Ling Zhu,
  • Brian D. Harris,
  • Cameron E Markowitz
Jack A. Cadigan
Louisiana State University

Corresponding Author:[email protected]

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Navid Jafari
Louisiana State University
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Nan Wang
Northeastern University
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Qin Jim Chen
Northeastern University
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Ling Zhu
Northeastern University
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Brian D. Harris
Louisiana State University
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Cameron E Markowitz
Stantec Consulting Services
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Abstract

Mechanisms that control marsh edge erosion include wind-generated waves, vegetation, mudflats, anthropogenic factors, and geotechnical properties of sediments. However, existing models for predicting marsh edge evolution focus primarily on edge retreat rates as a function of wave energy while accounting for other controlling factors as empirical constants. This simplification rises from a lack of high frequency monitoring of marsh evolutions. In particular, marsh erosion is time-scale dependent and conducting field observations on short time and spatial scales could elucidate the progression of erosion, which may improve marsh erosion predictive models. This study developed and validated a near continuous camera monitoring system to document marsh edge erosion at a high frequency in Terrebonne Bay, Louisiana. Erosion pins were monitored with the cameras and daily erosion rates were estimated. This was supplemented with daily wave power to explore the relationships between daily erosion and wave power. The largest magnitude erosion events are driven by a buildup in wave energy over a seven-day time period coupled with a strong one-day wave event, indicating a gradual reduction in marsh edge resistance with continued wave attack. Long-term erosion monitoring methods, including monthly field visits, smooths over the large magnitude short-term erosion events. For example, satellite and aerial imagery provide a long period of record, but they seem to underestimate the average annual erosion rate in the region, the effect of which may become exasperated over the varying temporal scales considered in the planning efforts of projects meant to protect the Louisiana coastline.