The document summarizes a case study comparing the erosion control performance of North American Green's C350 matting to standard 12-inch rock riprap in a drainage channel near Gulfport, Mississippi. Six months prior to Hurricane Georges hitting the area, the two lining materials were installed in the channel. [1] During the hurricane, flood waters exceeded channel capacity, undermining the rock riprap and washing it away while leaving the C350 intact with only minor vegetation loss. [2] The C350's coconut fiber matrix and permanent net structure provided superior erosion protection and reinforcement of vegetation compared to the rock riprap. [3] As a result, the contractor concluded that the C350 "saved the channel" and much of the

1. Background
The 1998 Atlantic hurricane season reared its fitful head with unexpected intensity, proving to
be the worst hurricane season in the last 200 years. In September alone, four hurricanes—
Georges, Ivan, Jeanne, and Karl—slammed the Atlantic and Gulf coasts of the United States
like a wrecking ball, devastating nearly everything in their paths. Not since 1893 had these east-
ern coasts dealt with such meteorological chaos during the course of one month.
The second largest of the September hurricanes was Georges, which rampaged across the
Caribbean, the Florida Keys, and into the Mississippi Delta with sustained winds of 150
miles/hour (241 km/hr) driving torrential rain. About six months before the storm arrived, a par-
ticular drainage channel located merely five miles from the coast near Gulfport, Mississippi was
used as grounds for comparing the erosion control performance of North American Green’s
C350 to that of standard 12 inch, fabric-backed rock riprap. Although unforeseen, the ensuing
hurricane activity provided the ultimate testing grounds for such a comparison.
Problem
The drainage channel was designed with a 30-50 foot (9-15 meter) wide bottom, 2:1 side slopes,
and a 2 percent bed slope gradient to handle 100 year storm drainage from thousands of acres
of both agricultural and residential land. An important engineering consideration was the fine
textured, highly erodible white sand blanketing the area. Such fine-grained material provides lit-
tle resistance to the force of flowing water, being easily displaced by flows exerting shear stress
as low as 0.02 lbs/ft2
. As well, the sand has very poor moisture holding capacity, making it a dif-
ficult medium for the establishment of vegetation.
To protect against erosion and re-estab-
lish turf, the side slopes of the channel
were covered with North American
Green’s C350 as supplied by Geo-
Products, Inc. in Madison, MS. In areas
where inlet pipes drain into the channel
and bends occur, the engineering plan
called for fabric-underlain 12 inch (30
cm) rock riprap. However, six months
after installation of the C350 and riprap,
Hurricane Georges ushered in the sec-
ond of two violent storms to impact the
channel within weeks of one another.
The prevailing storm proved to be the last for the already frail riprap lining sections of the chan-
nel. With flow estimated in excess of 2500 cubic feet per second (ft3
/s) [71 (m3
/s)] flood water
topped the 15 foot (4.57 m) high channel banks by two feet (60 cm).This high channel flow acted
to undermine the fabric-underlain rock riprap, carrying away a significant amount of soil and
hurling rock down the channel’s bed.
CASE
STUDY
Volume 5
Number 2
Nov. 1999
14649 Highway 41 North
Evansville, Indiana 47711
812-867-6632 In Indiana
1-800-772-2040
1-800-448-2040 In Canada
FAX 812-867-0247
Hurricane Forces
Prove C350’s Superiority
To Rock Riprap

2. Solution
Designed as a permanent channel lining, the C350 incorpo-
rates a coconut fiber matrix sewn between a permanent
three-dimensional polypropylene net structure. This dense
coconut fiber matrix allows the matting to provide the required
temporary erosion protection for the underlying soil prior to
vegetation establishment. After establishment, the C350’s net
structure permanently reinforces grasses at the stem and root
systems, providing increased structural stability for the loose
sandy soils.
In sharp contrast to the riprap sections, there was no appre-
ciable damage to the C350 or significant removal of soil from beneath the matting. Likewise, vegetation that had
established through the matting remained intact throughout the intense channel flows. The C350’s organic fiber
matrix acted to effectively retain moisture on the sandy soil surface, aiding in rapid seed germination and plant
growth. Although Hurricane Georges impacted the coast before vegetation became fully established in the chan-
nel, the high tensile strength of the C350’s three dimen-
sional net structure was able to resist damage even
when entire mature trees were dragged across its
surface and deposited by the flood waters. Published
installation instructions were closely followed and the
contractor was careful to entrench all terminal edges to
reduce the probability of the mat being undermined.
Because of the non-cohesive sandy soils, 12 inch
(30 cm) steel pins were used to better secure the C350.
Even with only a partial vegetative cover established,
the C350 had formed a strong barrier to resist
the tremendously erosive forces of wind-driven water in
the channel.
Results
“The C350 saved that channel,” proclaimed
the contractor after flood waters had reced-
ed and the damage could be assessed.
Nearly a year and a half later, much of the
damaged rock riprap is, not surprisingly,
being replaced by North American Green’s
C350. The C350 performed its intended
function flawlessly in the face of dire cir-
cumstances at only $7.00/yd2
installed—a
rather inexpensive endeavor considering
the failed rock riprap came at a cost of
about $24.00/yd2
. Thanks to the C350 mat-
ting, the channel in Gulfport, Mississippi is
rapidly recovering much as the surrounding
communities are in the wake of 1998’s
relentless hurricane season.