Geosynthetics October/November 2019 - 42

Nature area drainage control with GCCM

while minimizing long-term maintenance
costs, the city decided to install a permanent drainage ditch to collect runoff water
from the hillside and trail and direct it to
storm inlet drains. This ditch would also
improve the safety of the trail by reducing
erosion rills and gullies. Existing storm
inlets are shown in Figures 3a and 3b.

2a

Determining the most
effective armoring protection
for the drainage ditch

Background of specific runoff
and erosion issues along a
hiking trail

2b

FIGURES 2a and 2b Access paths and
hiking trails used for maintenance work
in the hilly area

42

Geosynthetics | October November 2019

The city has miles of hiking trails-which
offer breathtaking views of the surrounding mountains, valleys and the ocean-
along the hilly terrain that are only accessible with small equipment (Figures 2a
and 2b).
The hillside is maintained for fire protection, weed abatement and erosion control, which requires strategic vegetation
management including removal or maintenance to reduce the potential of fuel for
a fire. These hillsides and trails can be
point sources for erosion, soil stabilization and water quality issues during the
winter months. The average cumulative
rainfall is 15 inches (38.1 cm), and in the
2016-2017 season it was 20 inches (50.8
cm). The heavy rains arrive in January,
which typically account for 30%-50% of
the total, and the rainfall can be intense
within a short time period. The soils of
the San Juan formation are mostly clay.
To reduce erosion control, soil stabilization and runoff water quality issues

The city reviewed several solutions for
armoring the drainage ditch, specifically
considering whether each option would
meet the project criteria: overall installation and maintenance cost, erosion
protection, water quality impact, minimum impact and disturbance to hiking
trails or hillsides, increased water flow
capacity, minimum disturbance to hikers and residents during construction,
installation time, minimum long-term
maintenance, aesthetics, and safety. The
solutions considered included:
* Turf reinforcement mat
* Riprap
* Tied or articulate concrete block mat
* Shotcrete/poured concrete
* Fabric-formed concrete
* Geosynthetic concrete composite mat
Below is a summary of the review
findings for each potential solution for
the project.
Turf reinforcement mat (TRM)
TRMs are geosynthetic products that create a holding capacity for the vegetation
root system to increase its permissible
shear force during movement or flow of
water and to minimize erosion and water
quality issues. TRMs require that permanent dense vegetation be established at all
times. With the concerns of the constant
vegetation maintenance, increased fuel
for a fire, saturating the subsurface soils



Geosynthetics October/November 2019

Table of Contents for the Digital Edition of Geosynthetics October/November 2019

Geosynthetics October/November 2019 - Cover1
Geosynthetics October/November 2019 - Cover2
Geosynthetics October/November 2019 - 1
Geosynthetics October/November 2019 - 2
Geosynthetics October/November 2019 - 3
Geosynthetics October/November 2019 - 4
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Geosynthetics October/November 2019 - Cover3
Geosynthetics October/November 2019 - Cover4
Geosynthetics October/November 2019 - Blank1
Geosynthetics October/November 2019 - GeoConf20_1
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Geosynthetics October/November 2019 - GeoConf20_5
Geosynthetics October/November 2019 - GeoConf20_6
Geosynthetics October/November 2019 - GeoConf20_7
Geosynthetics October/November 2019 - GeoConf20_3
Geosynthetics October/November 2019 - GeoConf20_8
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