Geosynthetics February/March 2021 - 10

UPDATE

Stabilizing Oyster Lake's outfall
Preserving a unique ecosystem with an environmentally
friendly solution
By Drew Loizeaux

PROJECT HIGHLIGHTS
STABILIZING OYSTER
LAKE'S OUTFALL
OWNER

Walton County, Fla.
LOCATION

Santa Rosa Beach, Fla.
CONTRACTOR

RBM Contracting
DESIGN ENGINEER

Dewberry
GEOSYNTHETICS PRODUCT

ARMORMAX
GEOSYNTHETICS MANUFACTURER

Propex GeoSolutions

Geosynthetics | February March 2021

oastal dune lakes are freshwater lakes located within 2 miles (3.2 km) of an ocean
coastline. These rare ecosystems are only found in a handful of locations around
the globe, including Madagascar, New Zealand, Australia and Walton County, Fla.
Walton County is home to 15 coastal dune lakes, some of which are only a short distance from the Gulf of Mexico. These unique waterways create transitory interchanges
between a natural stormwater lake and the gulf. When a coastal dune lake reaches a
high water level, it will break through the dune system, forming a channel between
the lake and the gulf. The channel, or outfall, is critical for regulating water levels and
mitigating flooding
Oyster Lake is one of the coastal dune lakes located in Walton County. Major
storms caused Oyster Lake's outfall to become blocked, and urban growth along
Highway 30A was causing strain on its overall health. If the outfall remained blocked,
it would eventually release thousands of gallons of water, causing flooding to nearby
vacation homes.
The county was able to restore the outfall, but it and Walton County residents
wanted to reinforce the outfall to protect from future blockages and flooding. In
addition to stabilizing the outfall's channel, another goal of the project was preserving
the natural beauty of Oyster Lake. A solution that promotes vegetation was needed,
so hard armor reinforcements like rock riprap and concrete block were not options.
ARMORMAX Engineered Earth Armoring Solution was selected to reinforce the
channel sides of the outfall. This system was chosen because it provides slope stabilization and erosion control while promoting vegetation. Another important concern for
the project was the impact the reinforcement solution would have on the ecosystem,
which is home to several endangered species including the Choctawhatchee beach
mouse, snowy plover, and loggerhead and green sea turtles.
The engineered earth armoring solution is composed of PYRAMAT high-performance turf reinforcement mats (HPTRMs) and engineered earth anchors that work
together to lock soil in place and protect against hydraulic stresses. The HPTRM's
carbon footprint is 5.6 pounds (2.5 kg) of CO2e per 11 square feet (1 m2) of material.
This is about the same impact as driving for 7 miles (11 km). Comparatively, concretebased alternatives for erosion control are up to 10 times or more higher, ranging from
44 to 77 pounds (20 to 35 kg) of CO2e per 11 square feet (1 m2).
The HPTRM is an engineered plastic made from woven polypropylene. The
growing concern over plastics and their impact on the environment, specifically
the oceans, was a consideration. It is important to recognize that there are several

Geosynthetics February/March 2021

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