Geosynthetics October/November 2019 - 26

Reinforcing dunes and
bluffs with geosynthetics
By Brian Maggi, Christopher D. P. Baxter, Aaron Bradshaw, Annette Grilli and Naser Al Naser

Brian Maggi, P.E., M.ASCE, is a Ph.D.
candidate at the University of Rhode Island
in Kingston, a commander in the U.S.
Coast Guard and an assistant professor in
civil engineering at the U.S. Coast Guard
Academy in New London, Conn.
Christopher D. P. Baxter is a professor
in ocean/civil and environmental
engineering at the University of
Rhode Island in Narragansett.
Aaron Bradshaw is an associate professor in
civil and environmental engineering at the
University of Rhode Island in Kingston.
Annette Grilli is an associate research
professor in ocean engineering at the
University of Rhode Island in Narragansett.
Naser Al Naser is a former graduate student
in ocean engineering at the University
of Rhode Island in Narragansett.
All figures courtesy of the authors unless otherwise noted.

Geosynthetics | October November 2019

he devastating effects of recent hurricanes and nor'easters highlight the need
to improve the resilience of coastal communities. There is a trend toward
implementing "soft" engineering solutions such as dunes reinforced with geotextile
sand containers (GSCs) or coastal bluffs stabilized with geotextile tubes to improve
resiliency rather than traditional hardened structures like stone revetments. These
have the potential to protect communities from some storm events (e.g., 25- or 50year storms) while at the same time providing flexibility in design considering the
uncertainty regarding rates of sea level rise and storm frequency. However, there are
currently no accepted design standards for these geosystems, and general permit
requirements vary state to state. While numerous lab experiments and numerical
models have been developed to predict the hydraulic stability of coastal revetments
made of GSCs and geotextile tubes, there has been limited in situ validation of GSC
systems, especially when they are used to reinforce a natural system (Dassanayake
and Oumeraci 2012).
The construction of a GSC-reinforced dune in Montauk, N.Y., in 2016 and a coastal
bluff stabilized with geotextile tubes in Nantucket, Mass., in 2014 present excellent
opportunities to assess the resilience, stability and impact of storms on these systems
along with the maintenance requirements necessary to ensure longevity of the geotextiles and minimize the container impacts on adjacent natural environments. The
Montauk monitoring program being conducted by the authors includes the use of
interferometric sonar for nearshore bathymetry, real-time kinematic (RTK) differential
GPS, ship-mounted LIDAR, and unmanned aerial vehicles (UAVs) with structure from
motion (SfM) photogrammetry to develop cross-shore profiles and digital elevation
models (DEMs) before and after storm events for the site. The Nantucket monitoring
program is run by the Siasconset Beach Preservation Fund (SBPF) and project updates
are regularly posted on SBPF's website, www.sconsetbeach.org. Observations from the
Montauk site are being used to calibrate erosion modeling of a reinforced dune/beach
cross section using the wave propagation and sediment transport model XBeach and
to validate the performance and stability of the GSCs. The Nantucket site provides
additional background when assessing the level of monitoring and maintenance
required for a reinforced natural system in a state where coastal protection systems
are heavily regulated.

http://www.sconsetbeach.org

Geosynthetics October/November 2019

Table of Contents for the Digital Edition of Geosynthetics October/November 2019