Geosynthetics August/September 2019 - 48

GSI NEWS

By Robert M. and George R. Koerner

Commentary on flood abatement
using geosynthetics
GEOSYNTHETIC
INSTITUTE
GSI's mission is to develop
and transfer knowledge,
assess and critique
geosynthetics, and provide
services to the member
organizations.

www.geosynthetic
- institute.org

Robert M. Koerner's interest in
geosynthetic materials spans
nearly 40 years of teaching,
writing and consulting. His
pioneering work has helped
generations of educators,
researchers, designers,
manufacturers and regulators.

George R. Koerner is the
director of the Geosynthetic
Institute in Folsom, Pa.

n Sept. 8, 1900, a Category 4 hurricane struck Galveston, Texas, which is situated on the
Gulf of Mexico about 8 feet (2.4 m) above sea level. The storm created a 15-foot (4.6-m)
storm surge, killing 8,000 to 12,000 people and causing massive destruction. Subsequently,
four actions were taken by public officials and private homeowners. First, a large structural
seawall was constructed of concrete 17-feet (5.2-m) high and 16-feet (4.9-m) thick at its base.
It is 10-miles (16-km) long. Second, much of the undeveloped city (along with more than
2,100 destroyed or severely damaged buildings) was subsequently raised as much as 17 feet
(5.2 m). Third, some private owners elevated their homes on wooden substructures. Fourth,
many families and businesses left altogether.
Today, 10% of the world's approximately 7.5 billion people live within 33 feet (10.1 m)
of sea level, and many more live at slightly higher elevations but very close to coastlines.
Protecting people, structures and property as sea levels continue to rise in the years ahead
promises to be one of the great mega-engineering challenges of the 21st century and beyond,
said Robert J. Nicholls, professor of coastal engineering at the University of Southampton,
during a recent meeting at the National Academy of Engineering. In a complementary manner, Dr. Sean Vitousek and his coauthors at the U.S. Geological Survey (USGS) recently demonstrated that 4 inches (10 cm) of sea level rise, which is expected in the near term, can more
than double the frequency of coastal flooding for many locations around the globe. The full
report, "Doubling of Coastal Flooding Frequency within Decades Due to Sea-Level Rise," is
published online in Nature Science Reports at www.nature.com/articles/s41598-017-01362-7.
As a flood abatement strategy, there are several geosynthetic systems that can mitigate
or hopefully even eliminate such severe flooding. They are usually less expensive and/or
require less space (called "footprint") than the Galveston options. The focus here will be on
describing four of them: (i) geosynthetic-reinforced steep soil slopes, (ii) single or stacked
geotextile tubes, (iii) steel strut-supported geomembranes, and (iv) interconnected polymer
sheeting. These four alternative solutions are shown in Figures 1a-1d; the following are brief
discussions of these alternatives.
Geosynthetic reinforced walls and steep soil slopes have been a successful and ongoing
technology for some forty years and are incorporated under the generic terminology of
mechanically stabilized earth (MSE) systems. In this regard, layers of geogrids or geotextiles are used with native soil so as to form a coherent mass that has no technical height
limit. Thousands of such systems have been built worldwide due mainly to their straightforward construction, resulting low cost, and (in this case) low footprint in comparison
to unreinforced soil embankments such as flood control levees. It should be noted that
the side facing the water can be protected by a geomembrane for both seepage control
and wave impact.
Geotextile tubes began as erosion control systems in 1957 and have been growing in size
on a regular basis. The infill material is usually sand but can be cementitious materials as
well. The maximum height of an individual tube is presently 6.6 feet (2.0 m) but tube stacking is customary for greater heights. It should be noted that a variation of tubes is extremely
large sandbags, which have been used with reasonable success.

http://www.geosynthetic http://www.institute.org http://www.nature.com/articles/s41598-017-01362-7

Geosynthetics August/September 2019

Table of Contents for the Digital Edition of Geosynthetics August/September 2019