Developed barrier island adaptation strategies to hurricane forcing under rising sea levels
S. M. Smallegan1, J. L. Irish2, A. R. van Dongeren3
1Assistant Professor, Department of Civil, Coastal and Environmental Engineering, University of South Alabama, Mobile, AL 36688, USA, , 251-341-3998, corresponding author
2 Professor, Department of Civil and Environmental Engineering, Virginia Tech, Blacksburg, Virginia 24061, USA,
3Senior Researcher, Department of Marine and Coastal Management, Deltares, Delft, The Netherlands,
For submission to Climatic Change.
Online Resource 2
Inundation of land below mean higher high water under sea level rise scenarios
The mean higher high water (MHHW) datum is the average of the higher high tide water levels for each day over the data collection period (NOAA Tides and Currents, 2015); thus, land elevations that fall below the MHHW datum are assumed to be inundated during at least one of the two high tides experienced each day. Presently in Bay Head, the MHHW datum for our study area reaches the toe of the berm on the ocean side and only slightly inundates the back barrier region on the bay side (Fig. 1). As sea levels rise, the future MHHW datum will also rise, whereas the NAVD88 datum will remain static. We determine future MHHW datums by superimposing SLR scenarios onto the present-day MHHW datum (Table 1). Then, the inundation extent of future high tide, as determined by the elevation of the future MHHW datum relative to the static NAVD88 datum (Table 1), is analyzed on the present-day topography. This approach, often referred to as the drowned valley or “bathtub” approach (Leatherman, 1990), is applicable for analyzing static impacts only, or impacts of SLR on the barrier island assuming the present-day topography remains unchanged into the future. Barrier islands are dynamic in nature and are sensitive to changes in sea level; therefore, the inundation extent of MHHW under SLR (Fig. 1) is used only as a first estimate of barrier island flooding due to tides. The actual impacts of tides as sea levels rise will greatly depend on the future evolving topography.
Table 1 Past and projected MHHW datum elevations relative to present-day MHHW and NAVD88
SLR / MHHW relative to present-day MHHW (m) / MHHW relative to NAVD88 (m)-0.2 m / -0.2 / 0.4
0 m / 0.0 / 0.6
+0.2 m / +0.2 / 0.8
+1.0 m / +1.0 / 1.6
+2.2 m / +2.2 / 2.8
Inundation extents on the ocean and bay sides for SLR = +0.2 m, +1.0 m and +2.2 m are shown in Fig. 1. Results reveal relatively minor inundation on the ocean side (right side of grid) but major inundation on the bay side (left side of grid). For SLR of +0.2 m, the beach is inundated by an additional 1 m in the cross-shore direction and an additional 4 m on the bay side in areas that are particularly low-lying. Horizontal inundation distances increase to 7 m ontheoceansideand220monthebaysideforSLR=+1.0m. Onlythedune (=700m) remains above MHHW for SLR = +2.2 m and the entire back barrier region is flooded during high tide. These inundation extents are comparable with those estimated for regional static impacts of SLR by NOAA’s National Ocean Service (National Ocean Service, 2015). This projected inundation demands action to protect the developed barrier island as sea levels rise, and several adaptation strategies are evaluated to this end in this study.
Fig. 1 Water inundation map of the study area in Bay Head, NJ on the ocean (right) and bay (left) sides under present-day MHHW (heavy gray solid), SLR = +0.2 m MHHW (black dot), SLR = +1.0 m MHHW (gray solid), and SLR = +2.2 m MHHW (black solid). Buildings are represented by gray polygons and the buried seawall is located beneath the dune (vertical dash-dot)
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