Geotextile

January 06, 2023

One of the articles inside my local newspaper this week reported on the effectiveness of emergency berm installed on St. John’s County beach in Florida.  The FEMA Dune Enhancement Project was begun last year to create the berm to keep the beaches from eroding.  It was not yet finished when the beaches were hit by Ian and Nicole.  The berms were developed as a temporary protection while engineers worked on long term plans to prevent beach loss.  The county had installed 480,000 cubic yards of sand along the 11 mile stretch.  Rather than dredging the sand from the ocean floor, officials hauled sand by truckloads from 65 miles (104.5 km) away.  Beach managers are now focusing attention on where and how fast they can start repairing beaches damaged by last years’ storms.  The foundation of the emergency berm was geotextile.

When I looked online, I found geotextile tubes are large bags made of permeable woven geotextiles, which are stronger than standard sandbags.  The tubes are used in many civil engineering and erosion control projects like embankments, retaining walls, reservoirs, bank protection and stabilization, as well as coastal erosion control.  Geotextiles are permeable fabrics typically made from polypropylene or polyester.  The fabrics come in a woven (resembling mail bag sacking) and nonwoven (resembling felt) form.  Geotextile was intended to be a substitute for granular soil filters and use began in the 1950’s with R.J. Barrett using woven geotextile fabric in conjunction with concrete seawalls, control blocks, and under stone riprap.  Barrett used different styles of woven monofilament fabrics.  After installation, the area around the geotextile tubes must be further stabilized by sodding or planting.  Vegetation is highly important for erosion control because plant root systems help hold soil and sand in place and create a more natural look.  The geotextile also helps clean rainwater runoff of fertilizers and other harmful chemicals.

While beachgoers do not seem to care about the nature of sand used to cover the geotextile, and its color, are a major concern for sea turtles.  Scientists have recently seen a concerning ratio of males to females due to the hotter summers.  The temperature of the sand determines the sex or gender of a sea turtle, with more females born during warmer summers and males preferring cooler temperatures.  Florida’s average summer temperature is on an upward trend, with the past three years (2019 – 2021) being among the warmest on record.  That meant only females hatched, and only one in 5,000 sea turtles makes it to adulthood.  Males hit maturity around 20 years of age and females around 35.  They spend their youth in the open ocean foraging then return to the beaches where they hatched to breed.  Ladies breed every two to three years and will produce 3 – 5 nests with around 100 eggs each in a single season.  The Endangered Species Act classifies the Northwest Atlantic Loggerhead (Caretta caretta) as threatened, which means the species is likely to become endangered in the future.

THOUGHTS:  The beach on the lake where Melissa and I took Zena to last week is covered with black, fibrous layers of what appears to be rubber or fabric.  It had obviously been put down and then covered with sand to protect the beach from the waves that wash across the half mile (800m) wide lake.  I never knew what to call the fabric until now.  It is a nonwoven version of the geotextile reported in my newspaper.  As lake levels rise and fall (it is a reservoir) the geotextile protects much of the sand from washing away.  While we have no sea turtles, shore habitat is still critical for a healthy ecosystem.  Act for all.  Change is coming and it starts with you.

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