Geosynthetics June/July 2019 - 34

Streambank restoration using engineered bank stabilization

FIGURE 2 The Red Bank Elementary "Stream
Team" assesses the existing streambank
erosion to better understand the associated
impacts to water quality and aquatic habitat
prior to restoration.

chose a combination of SCOURLOK
Engineered Bank Stabilization (EBS)
and ARMORMAX 75 Engineered Earth
Armoring Solutions (EEAS).
EBS is a new system/best management practice to resist extreme hydraulic stresses. EBS systems are designed
to help protect streambanks, shorelines
and other similar applications while promoting vegetation in lieu of hard armor.
Additionally, it provides water quality
benefits including pollutant and nutrient removal. The EEAS was used to stabilize the slope above the streambank
to prevent erosion from larger runoff
and flooding events. This system combines geotextiles and a high-performance
turf reinforcement mat (HPTRM) with
engineered earth anchors (EEA) to provide additional surficial slope stability
(HPTRM + EEA). Figure 3 depicts the
typical layout used on the Mountain
Creek streambank restoration project.

ARMORMAX
Vegetation

Geosynthetics | June July 2019

In recent years, as site conditions allow,
project designers have sought vegetated
facing on these structures rather than
traditional hardscape systems (i.e., rock
riprap/rockery, concrete blocks or rockfilled wire-frame units). An EBS system
acts as a vegetated gravity retaining wall.
Gravity retaining walls rely on the weight
of the wall system itself to counteract the
lateral earth pressures due to the retained
soil. The most common gravity walls currently in use are comprised either of rockfilled gabions or of large concrete blocks,
each weighing 1,800 pounds (816 kg) or
more that interlock together in a dry-stack
fashion to construct retaining walls typically up to 12 feet (3.6 m) high. To reach
such heights without additional artificial reinforcement, the face batter angle
is increased to 12˚-16˚ and/or a wider
(thicker) base block is used on the bottom
course of blocks to increase resistance to
base sliding and to overturning moments.

Components and capabilities

FIGURE 3 Isometric view of EBS system and HPTRM + EEA

SCOURLOK

Gravity retaining walls

The EBS system essentially is comprised
of a pyramidal-woven HPTRM and rigid
galvanized (or stainless) welded metal
cells that are internally lined with nonwoven geotextile that form compartmentalized units 3 feet thick × 4 feet high × 15
feet long (0.9 × 1.2 × 4.6 m). Each unit is
then comprised of five cell compartments
that are 3 × 3 × 4 feet (0.9 × 0.9 × 1.2
m) and are open at the bottom and top,
which allows ready setup and filling at the
project site (Figure 4). When several of
these units are linked together in a series,
they form a gravity wall system that is 4
feet (1.2 m) high and 3 feet (0.9 m) thick.
The EBS system can be shipped folded
and flat, then expanded out like an accordion, transforming into the segmented
units that can be stood up on a level,
prepared surface and then filled from the
open top with soil or gravel.

Geosynthetics June/July 2019

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