Geosynthetics February/March 2021 - 24

Comparative analysis of the flow and filtration capabilities of sediment retention devices

performance of a variety of linear SRDs,
providing insight into the appropriate usage of these products in design.
Consequently, this article will demonstrate the ability of these test methods
to differentiate product performance
and, in so doing, enable specifiers to
engineer the appropriate SRD system
to provide the desired balance between
flow and sediment retention during
construction operations.

While sediment ponds
have been widely
studied and have
generally accepted
quantitative design
procedures, this is not
the case for most other
BMPs, including SRDs.
SRDs offer the potential
to prevent water
pollution without the
large area requirement
and safety concerns of
a sediment pond.

Standardized testing of SRDs
While sediment ponds have been widely
studied and have generally accepted
quantitative design procedures, this
is not the case for most other BMPs,
including SRDs. SRDs offer the potential
to prevent water pollution without the
large area requirement and safety concerns of a sediment pond. Unfortunately,
SRDs are frequently selected without
a quantitative means of knowing if the
device can be expected to perform sufficiently. Without standardized test
procedures, there is no generally recognized way for specifiers/designers
to verify marketing claims or onetime
field trials, or for innovators to reliably
test new products. Standardized testing procedures assist the users of SRDs
in establishing improved construction
specifications. Owners and contractors
can save money by installing the correct
SRD for the expected site conditions.
Additionally, product manufacturers
have a clear, recognized methodology
for establishing product capabilities.
Testing SRD performance
in sheet flow applications
SRD material components can be accurately evaluated in a laboratory for
hydraulic properties using the benchscale standard test method, ASTM
D5141. Yet, the effectiveness of many
SRD systems is installation dependent.

Geosynthetics | February March 2021

Therefore, a large-scale test that can
incorporate the full-scale " as installed "
condition is the ideal evaluation procedure. These needs are addressed by the
large-scale standard test method ASTM
D7351. These test methods are both
able to quantify sediment removal and
associated flow rate through an SRD,
so that the potential for either excessive
sediment loss or the backup of runoff
can be assessed.
Summary of test method
ASTM D5141
Test method ASTM D5141 quantifies
the ability of an SRD to retain eroded
sediments carried by flowing water
under bench-scale conditions. In the
test method, sediment-laden water of a
known concentration and sediment type
is allowed to flow up to and through
the filtration component of an SRD.
The filtration component of an SRD is
often the geotextile or fabric portion of
the SRD. However, some SRDs, such as
compost socks, utilize both a geotextile
mesh and a compost filtration component encased within the geotextile
component. The filtration component
of an SRD should not be confused with
the structural component(s) of an SRD.
Examples of structural SRD components
include T-posts in a silt fence system,
metal grate inserts of an inlet filter system and wooden stakes used in a compost sock installation.
At a minimum, the effluent water
and ass o ciate d s e diment p assing
through the SRD is measured and
compared to the influent, or delivered, water and associated sediment to
quantify the effectiveness of the SRD
in retaining sediments while allowing
water seepage. This test method may
also assist in identifying physical attributes of SRDs, such as apparent opening size, permeability or tensile strength
that contribute to an SRD's ability to

Geosynthetics February/March 2021

Table of Contents for the Digital Edition of Geosynthetics February/March 2021