Impacts of Coastal Infrastructure on Shoreline Response to Major Hurricanes in Southwest Louisiana

Abstract

The Rockefeller Wildlife Refuge, located along the Chenier Plain in Southwest Louisiana, was the location of the sequential landfall of two major hurricanes in the 2020 hurricane season. To protect the rapidly retreating coastline along the Refuge, a system of breakwaters was constructed, which was partially completed by the 2020 hurricane season. Multi-institutional, multi-disciplinary rapid response deployments of wave gauges, piezometers, geotechnical measurements, vegetation sampling, and drone surveys were conducted before and after Hurricanes Laura and Delta along two transects in the Refuge; one protected by a breakwater system and one which was the natural, unprotected shoreline. Geomorphological changes were similar on both transects after Hurricane Laura, while after Delta there was higher inland sediment deposition on the natural shoreline. Floodwaters drained from the transect with breakwater protection more slowly than the natural shoreline, though topography profiles are similar, indicating a potential dampening or complex hydrodynamic interactions between the sediment—wetland—breakwater system. In addition, observations of a fluidized mud deposit in Rollover Bayou in the Refuge are presented and discussed in context of the maintenance of wetland elevation and stability in the sediment starved Chenier Plain.

Beach Profile, Water Level, and Wave Runup Measurements Using a Standalone Line-Scanning, Low-Cost (LLC) LiDAR System

“…The prototype LLC LiDAR consists of six major components: [1] Slamtec RPLiDAR A1M8 (R5) 360 • laser range scanner (USD 110); [2] Raspberry Pi 3B+ single board computer and 32 GB microSD card (~USD 40, in 2020); [3] Anker PowerCore+ 26,800 mAh PD USB battery pack (USD 140); [4] 3D printed (PLA), custom-designed mounting bracket (<USD 2); [5] Polycase enclosure (Part # WC-41) (USD 45); [6] Polycase aluminum baseplate (Part # WX-42) (USD 13). The hole pattern aligned with the 3D printed mounting bracket was manually drilled into the aluminum baseplate.…”

“…The destructiveness of tropical cyclones has been increasing over the past several decades, which may be attributed to longer lived, more energetic storms [1], and to a higher frequency of occurrence and magnitude of rapid intensification [2,3]. This increase in destructiveness, coupled with rising coastal populations [4] and infrastructure demands [5], contribute to large economic cost of these storms [6].…”

“…Fully standalone, self-contained systems with low infrastructure requirements are necessary for rapid-deployability when predictions of location(s) that may experience the most significant impact(s) are uncertain or widespread. Low cost is also a high priority, due to potential loss of equipment during storm impact [3,20].…”

Near‐continuous monitoring of a coastal salt marsh margin: Implications for predicting marsh edge erosion

“…The salt marsh resistance to these external factors is linked to sediment dynamics, with a major emphasis placed on vertical accretion and relative sea‐level rise that links to interior marsh ponding (Cadigan et al., 2022; Day et al, 1998; FitzGerald et al, 2008; Kirwan et al, 2016; Pethick, 1993; Priestas et al, 2015; Temmerman & Kirwan, 2015; Temmerman et al, 2005). However, salt marshes are also inherently weak and vulnerable to shoreline retreat (i.e., marsh edge erosion) caused by waves from hurricanes and storms (Barras et al, 1994; Cadigan et al, 2022; Day et al, 2007; Jadhav et al, 2013). Analysis by Penland et al (2000) specifically shows that approximately 25% of the wetland loss in the Mississippi River Delta Plain from 1932 to 1990 was attributed to erosion due to wind‐driven waves.…”

“…Marsh edge erosion occurs when wind waves attack marsh boundaries (e.g., Bendoni et al, 2014; Leonardi et al., 2016; Leonardi & Fagherazzi, 2014; Mariotti & Fagherazzi, 2013; Marani et al, 2011; Schwimmer & Pizzuto, 2000; Wiberg et al., 2020). The factors influencing marsh edge erosion consist of severity of wind‐generated waves (Fagherazzi et al, 2006; Mariotti & Fagherazzi, 2010), vegetation root strength (D'Alpaos et al, 2007; Koppel et al, 2005; Paul & Amos, 2011), anthropogenic land use and land change (Gedan et al, 2009), and geotechnical properties of cohesive mudflat sediments (Bloemendaal et al, 2021; Cadigan et al, 2022; Feagin et al, 2009; Howes et al, 2010; Jafari et al, 2019). Existing models in Table 1 for predicting marsh edge evolution focus primarily on edge retreat rates as a function of wave energy, while accounting for other controlling factors into empirical constants, though recent work suggests that many salt marshes show a very weak or non‐existent relationship between wave power and erosion rates (Bloemendaal et al, 2022).…”