Geosynthetics April/May 2021 - 30

Comparative analysis of the flow and filtration capabilities of sediment retention devices-Part 2

In contrast to the
nonwoven geotextile silt
fence category, products in
the nonwoven composite
geotextile product
category are composed
of a multilayer nonwoven
geotextile component
impregnated, or filled,
with natural fibers. The
combination of multilayer
nonwoven fabric and fiber
impregnation leads to a
high-strength, relatively
thick filtration component
that provides a structurally
three-dimensional profile,
allowing high water flow
and soil capture.

Geosynthetics | April May 2021

are produced for purposes other than filtration, and caution should be used by a
designer when specifying nonwoven fabric
for deployment as a silt fence. Nonwoven
fabrics are utilized for reinforcement, separation and filtration, and it is unlikely that
every nonwoven fabric produced has the
material characteristics necessary to meet
the filtration and flow properties found in
this research.
Due to cost, nonwoven fabric may not
be the most appropriate solution for all
silt fence applications and may be most
appropriately utilized in areas where runoff concentrates prior to being released
off-site, thus requiring both high filtration
efficiency and moderately high flow rate.
Nonwoven composite geotextile silt fence
Eight products from the nonwoven composite geotextile product category were
tested via ASTM D5141 in this research.
Aside from the two noticeable outliers
in Figure 5 on page 32, this product
category provides excellent filtration
efficiency, with all products providing
greater than 90% filtration efficiency
and high flow rate. In contrast to the
nonwoven geotextile silt fence category,
products in the nonwoven composite
geotextile product category are composed
of a multilayer nonwoven geotextile component impregnated, or filled, with natural fibers. The combination of multilayer
nonwoven fabric and fiber impregnation leads to a high-strength, relatively
thick filtration component that provides
a structurally three-dimensional profile,
allowing high water flow and soil capture.
This product category, based on knowledge gained during the research, is relatively unique and not widely represented
within the industry.
Similar to nonwoven fabrics, the nonwoven composite fabrics may not be the
most appropriate solution for all silt fence
applications due to cost, but may be most
appropriately utilized in areas where runoff

concentrates prior to being released off-site
and, thus, both high filtration efficiency
and high flow rate are required. There may
be applications for the product category
in capturing nonsediment pollutants.
However, further investigation is required.
Three-dimensional filter socks and
fibrous wattles
Five products from the three-dimensional
filter sock and fibrous wattle category were
tested via ASTM D5141 in this research.
The data shows that this product category
provides moderately high filtration efficiency, with all tested products providing
greater than 80% filtration efficiency and
excellent flow rate. Three-dimensional filter socks and fibrous wattles are composed
of either a geotextile fabric or geotextile
mesh filled with compost, rock, straw, or
other agricultural or synthetic media.
Compared to all other tested products,
this product category is unique in that it
is a three-dimensional SRD and provides
a much lower vertical profile for filtration
in the field. This product category may be
both an economical and functional alternative to two-dimensional silt fence materials. However, caution must be used by
designers in specifying products from the
three-dimensional filter socks and fibrous
wattles category, as the lower vertical profile
will lead to greater maintenance/clean-out
requirements compared to two-dimensional silt fence products. Lack of maintenance/clean-out will lead to soil deposition
on the upstream face of the SRD. This soil
buildup will eliminate any vertical profile
for filtration and cause constant overtopping and lack of product efficacy.
Proprietary woven geotextile silt fence
Six products from the proprietary woven
geotextile silt fence category were tested
via ASTM D5141 in this research. The
data shows that this product category
provides poor filtration efficiency, with
products tested providing between 30%

Geosynthetics April/May 2021

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