High human influence on beach response to tropical cyclones in small islands: Saint-Martin Island, Lesser Antilles

Abstract

Using multi-date satellite imagery and field observations, this paper assesses the inferred impacts of September 2017 cyclones on the beaches of Saint-Martin Island. Twenty-two beaches out of 30 predominantly exhibited shoreline retreat, with the highest retreat value (-166.45 m) recorded on the north-eastern coast. While erosion predominated on beaches and at the sand dune front, inner areas generally exhibited accretion, with sand sheets (up to 135 m from the pre-cyclone vegetation line) indicating landward sediment transfer. Natural back-reef beaches exhibited the formation of new beach ridges, marked (up to 2 m) upward growth and alongshore beach extension. The high spatial variability of inferred impacts is attributed to the cyclone's track, coast exposure, beach configuration and, importantly, human-driven environmental change. Whereas vegetation removal exacerbated marine inundation and inhibited the vertical accretion of beaches, shoreline hardening aggravated wave-induced sediment loss while also inhibiting sediment deposition. Four beach response modes are distinguished. Based on findings, we identified three major areas of action for risk reduction and adaptation to climate change. Depending on beach response and site specificities, relocation and the determination of set-back lines, coastal buffer restoration, or engineered structures' upgrading should be prioritized.

Coastal Processes and Influence on Damage to Urban Structures during Hurricane Irma (St-Martin & St-Barthélemy, French West Indies)

“…The improved numerical model is in close agreement with previous results [30,57] regarding sea states. With significant wave heights reaching about 9-10m offshore, at 15-20m depth these values are in agreement with operational forecasts issued by Météo-France (Figure 5d), and suggest that significant wave heights are essentially limited by wave breaking on the east coast.…”

“…The WRF ARW atmospheric model [29] is used at 280-m resolution with 3D Large Eddy turbulence in order to examine Irma gust effects over Saint-Martin. A part of these results was published by [30]. This previous simulation setup was improved in the present study with (1) a higher resolution linked with an upgraded land-use map combining the 300 m ESA CCI landcover map and OpenStreetMap data, (2) the use of the 3D Large Eddy turbulence, which is more appropriate for turbulent wind gusts, and (3) a proper hurricane vortex initialization method.…”

Assessing the impacts of shoreline hardening on beach response to hurricanes: Saint-Barthélemy, Lesser Antilles

“…For example, overwash processes led to the deposition of sand, coral debris and blocks over distances that reached up to 70 m from the pre-cyclone vegetation line on Tubuai and Reunion islands, respectively in 2010 (TC Oli; Etienne, 2012) and 2014 (TC Bejisa; . In natural settings, sand and coral debris deposited by TCs may thus contribute to an increase in the elevation of low-lying coastal areas (Duvat et al, 2017b;Duvat et al, 2019). In contrast, in highly-developed settings, these deposits are often quickly removed and used for construction (Bush, 1991), which annihilates the abovementioned positive effect of TCs.…”

“…In contrast, in highly-developed settings, these deposits are often quickly removed and used for construction (Bush, 1991), which annihilates the abovementioned positive effect of TCs. Importantly, several studies emphasized the high spatial variability of cyclone-induced morphological changes on small islands' coasts over short distances, and even on the sediment cell scale (Cazes- Duvat, 2005;Etienne, 2012;Duvat et al, 2019). The nature (erosional vs. accretional) and severity of TC impacts are function of a variety of factors, including the cyclone track, island and shoreline exposure (which decreases with the presence of nearshore islets and of protruding headlands), the coastal system's geomorphic characteristics (i.e.…”

“…Instead, the reflection of storm waves by these structures contributes to beach narrowing by increasing erosion (Bush, 1991;Fletcher et al, 1997), which eventually leads to beach loss (Schlacher et al, 2006;Cambers, 2009;Cooper and Pile, 2014). Additionally, the establishment of tourist amenities in coastal areas has led, in many cases, to the destruction and replacement of the native vegetation by introduced species, which decreases the resistance and the resilience of coastal systems to TC impacts (Cambers, 2009;Duvat et al, 2017b;Duvat et al, 2019).…”