$4.00 SEPTEMBER/OCTOBER 2012 · 2020-02-20 · Subscription rates for printed copies: One year -...
Transcript of $4.00 SEPTEMBER/OCTOBER 2012 · 2020-02-20 · Subscription rates for printed copies: One year -...
SEPTEMBER/OCTOBER 2012$4.00
PLUS:BMPS used for STORMWATER INFILTRATION RETROFIT Mall project
SHORELINE STABILIZED by repairing liner with an engineered bentonite/aggregate composite
Improving vegetation establishment practices for SURFACE MINE RECLAMATION
WATERSHED APPROACH to streambank stabilization for erosion and fl ood control
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STAFF
Kenneth M. RaschPresident
Jane RaschVice President
Amy DencklauPublishing Editor
Martha SteinkampCirculation Manager
Emily JonesAssistant Editor
Angela DougallAccounting
SALES
Gail HenryAccount Executive
[email protected]: 515-227-5042 or
515-576-3191
Shanna EgliAccount Executive
CONTENTS
4 September/October 2012
Land and Water (ISSN 0192-9453) is published bimonthly by Land and Water, Inc., 320 A. Street, Fort Dodge, IA 50501-9925. Telephone (515)576-3191, Fax (515)576-2606. Land and Water is edited for contractors, engineers,
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of the magazine. No part of this publication may be reproduced without the written consent of the publisher. Land and Water assumes no responsibility for statements expressed by contributors. Jeremiah 29:11
DEPARTMENTS 6 Tell It Like It Is 53 Equip-Board 54 Advertiser’s Index
FEATURES
Volume 56, Number 5 September/October 2012
STORMWATER MANAGEMENT 8 Retrofitting a Major Retail Mall for Stormwater Volume Reduction The combined goals of phosphorus reduction and stormwater volume reduction to a nearby lake called for the retrofitting of stormwater BMPs at Maplewood Mall, Minnesota.
by Clifton Aichinger & Erin Anderson Wenz
STREAMBANK STABILIZATION 15 Multi-Objective Stream Stabilization in Fort Branch Creek Severe streambank erosion drove the City of Austin’s Watershed Protection Department to undertake three stream stabilization projects, all located on the same watershed at Fort Branch Creek, Texas.
by Morgan Byars, P.E. & Janna Renfro, P.E.
LAKES & PONDS 21 The Perfect Pond What must come together for a pond to be perfect?
by Bob Lusk
SOIL AMENDMENTS 25 Improving Vegetation Establishment Practices for Surface Mine Reclamation By utilizing a comprehensive approach that encompassed soil science, agronomy, and soil stabilization, vegetation establishment success rates were substantially increased on reclaimed surface mines within the Appalachian Coal Basin. by Brian Free, CPESC
SOIL REINFORCEMENT 29 Los Vaqueros Reservoir Expansion In order to expand the storage capacity of the Los Vaqueros Dam in California, MSE walls were constructed to increase the height of the dam. by Michele Curry
SHORELINE STABILIZATION 33 Liner Repair Using an Engineered Bentonite/ Aggregate Composite When locals at a Minnesota townhome development noticed their lake level dropping, they needed to find a solution for damage to the lake’s HDPE synthetic geomembrane liner. by Kevin VanTuyl & Brent Vatland
WETLANDS RESTORATION 36 Opportunity Ponds Wetlands – Adapting to Revegetation Variables A short growing season, low nutrient soils, and hungry wildlife provided many lessons at a wetland mitigation project in the Rocky Mountains of Montana.
by Leonard Ballek
EROSION CONTROL BMPS 45 Construction Site BMPs Challenging construction sites throughout the United States are requiring the use of a wide variety of BMPs.
by Donald Thieman, CPESC
FLOODPLAIN MANAGEMENT 50 Reaching Across the Aisle for Conservation Douglas County Nevada took up the challenge to develop the Douglas County Conservation Bill in order to maintain, preserve, and protect their community’s floodplain functions.
by Debra Turrieta
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ABOUT THE COVER
Multi-objective stream stabili-zation project on Fort Branch Creek in Austin, Texas at end o f cons t ruc t i on phase . Mechanically stabilized earth walls with vegetated geogrids and a meandering pi lot channel provide a natural aesthetic and function. The project will provide flood hazard reduction, erosion control and water quality pro-tection. See the full story on page 15.
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15www.landandwater.com
STREAMBANK STABILIZATION
The City of Austin has utilized numer-
ous stream stabilization techniques
over the years, evolving from fl ood-fo-
cused concrete and gabion designs to more
natural channel designs meant to restore
benefi cial stream function. What has be-
come a widely accepted popular standard
of practice is a system that includes natu-
ral limestone boulders for toe protection,
which are locally available, with native
riparian vegetation on the upper banks.
Th e boulder treatment usually extends be-
low the creek bed to the anticipated scour
depth and vegetated area begins above
the bankfull elevation. In many cases the
upper slopes are designed as a mechani-
cally stabilized earth system (MSE) using
geogrid reinforced soil lifts that allow for
vegetation establishment. Th e approach
to channel bed stabilization may include
constructed step-pools or riffl es for grade
control and a pilot channel to allow for
base fl ow that provides aquatic habitat.
Th is approach provides a reliable struc-
tural solution for solving both erosion and
fl ood control problems, while incorporat-
ing natural materials that help restore the
Multi-Objective Stream Stabilization in Fort Branch Creek
Reach 1 one year after construction.
16 September/October 2012
STREAMBANK STABILIZATION
riparian zone to the extent possible in the
urban context. Th e following case study
highlights several projects in the same wa-
tershed to illustrate how these techniques
are used to achieve multiple goals of ero-
sion control, fl ood control and stormwater
water quality protection.
Th e City of Austin’s Watershed Protec-
tion Department is guided by a 2001 City-
wide Watershed Master Plan that provides
unifi ed direction in fulfi lling the depart-
ment’s goal of protecting lives, property,
and the environment by reducing problems
associated with adverse fl ooding, erosion,
and stormwater pollution. A particular fo-
cus is given to solutions that demonstrate
a commitment to environmental responsi-
bility, cost-eff ectiveness, and sustainability.
Th e master plan identifi ed Fort Branch
Creek to be one of its highest priority wa-
tersheds within the city. Fort Branch Creek
drains a 3.5 square mile urban watershed
in East Austin and exhibits multiple char-
acteristics of an impaired stream – heavily
eroded channel and banks, degraded water
quality, and insuffi cient fl ood capacity for
the new fl ow regime.
The watershed experienced nearly full
build out several decades prior to the
implementation of the City’s watershed
protection stormwater management regu-
lations in the early
1980’s. Current reg-
u l a t i on s r equ i re
stream setbacks and
stormwater deten-
t ion to p reven t
potential problems
related to flooding,
erosion and water
quality. The effects
of rapid, uncon-
trolled urbanization
were apparent in the
results of the 2001
Watershed Master
Plan, as Fort Branch
showed some of the
more severe flooding
and erosion prob-
lems within the City.
To begin addressing
these issues, a comprehensive study of the
watershed was conducted by dividing Fort
Branch into eleven distinct geomorphic
reaches and providing detailed analysis of
each segment’s hydrology, hydraulics, geo-
morphology, sediment transport, and
environmental integrity.
To prioritize project areas within the
watershed a quantitative ranking system
was developed to assign problem scores and
a ranking for each stream reach related to
problems associated with fl ooding, erosion
and water quality. Based on the problem
scores, the three highest priority reaches
– Reach 1, Reach 6, and Reach 7 - were
selected to proceed to design and imple-
mentation. Th e primary driving factor for
all of these projects was severe streambank
erosion.
Alternatives for the channel design
where evaluated from a cost-eff ectiveness,
Reach 1 before construction.
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STREAMBANK STABILIZATION
sustainability and environmental impact
perspective. Th e range of solutions evalu-
ated included construction of a concrete-
gabion lined channel, natural boulder-veg-
etated mechanically stabilized earth system
and a non-structural solution of voluntary
home buyouts along the creek. Hydraulic
modeling showed that the concrete channel
was most eff ective at reducing water surface
elevations within the individual project
reaches, but the adverse environmental im-
pacts due to loss of stream habitat and eco-
system services were not acceptable based
on the City’s multi-objective approach to
watershed management. Additionally,
while this approach may reduce fl ooding
and erosion problems at the project loca-
tion, downstream channel reaches may ex-
perience unwanted increases in peak fl ows
and erosion as the energy is translated from
Reach 1 near end of construction.
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STREAMBANK STABILIZATION
18 September/October 2012
one location to another. Th e non-structur-
al home buyouts solution proved to be too
costly and not acceptable from a social per-
spective in that many residents would be
displaced from a well-established residen-
tial neighborhood. Rather selective volun-
tary acquisitions were off ered for owners in
isolated areas with severe fl ooding or ero-
sion and where a structural solution would
not be cost-eff ective for a single residence.
Th e preferred approach was the structural
stabilization using the natural limestone
boulders, vegetated banks, and pool/riffl e
bed forms to mimic natural channel mor-
phology. Not only was this approach less
costly, it provided benefi ts other than sta-
bility and fl ood hazard reduction. Th e fol-
lowing describes the three project areas in
more detail.
Reach 1
Th e fi rst project reach to go forward
was Fort Branch Reach 1 which included
2,200 linear feet of channel confi ned with-
in a 50 foot drainage easement between
backyards of single-family homes that
paralleled the creek. Channel erosion had
resulted in nearly vertical banks 10’ to 18’
high, presenting immanent threat to util-
ity poles, residential structures, fences, and
Left: Reach 7 Phase 1 after construction. Right: Reach 7 Phase 2 during construction.
19www.landandwater.com
STREAMBANK STABILIZATION
resident safety. Numerous yards experi-
enced massive slope failures resulting in the
loss of 10 to 20 feet of land on residential
lots. Near the upstream end of the proj-
ect a wastewater line that crosses the chan-
nel had become exposed by more than 4
feet due to years of channel down cutting.
Additionally most every house along this
reach was located in the in the 100-year
fl oodplain.
Th e fi nal design featured a mechani-
cally stabilized earth system using lime-
stone boulders and mechanically stabilized
earth soil lifts of both sides of the channel
for the entire project length. Th e boulders
measured 1.5’ by 2’ by 3’ and were stacked
two to three rows above grade with six-
inch horizontal off sets. Above the boul-
der toe, 18-inch soil lifts were constructed
with soil retention blanket, biaxial geogrids
and welded wire form facings. Not only
do the wire forms provide structural sup-
port for the soil lift facing, but they also
facilitate construction because each row of
lifts can be assembled in long continuous
spans. Within the geotextile fabric, the
front face of each lift was fi lled with top-
soil and seeded with native plants. Th e soil
lifts are stepped back with 1-foot off sets.
Above the soil lifts, the slope was gently
graded and revegetated with rooted plants
and trees. Geogrids between all layers pro-
vided additional stabilization of the entire
system. For drainage, gravel backfi ll was
used behind the boulders with 12” wide
stripdrains spaced 5’ on centers terminat-
ing at the topsoil layer. Th e ends of the
project key into the natural channel with a
rock riprap transition to stable bank.
Th e channel bottom ranged from 25‘
to 35’ and featured a 10’ wide meandering
pilot channel lined with coir logs. Where
the constructed meander neared the MSE
wall, rock riprap was placed at the base for
additional scour protection. Rock riprap
was used to place four grade controls to
maintain the channel at its equilibrium
slope. Th e eight storm drain outfalls locat-
ed within the project reach were realigned
to discharge at 45-degree angles in the di-
rection of fl ow and were protected with
rock riprap aprons. Th e exposed wastewa-
ter pipe was encased and a large rock riprap
grade control structure was constructed
to protect it from further undermining.
Th roughout the design phase, storm events
continued to wreak rapid havoc on Reach
1 such that an interim 450-foot emergency
project had to be constructed until the fi nal
project could be implemented.
Th e Reach 1 project not only stabi-
lized the channel banks, but also provided
signifi cant fl ood control benefi ts by lower-
ing the 100-year water surface elevation
below the foundation elevation of all but
fi ve homes. Th e total capital cost to imple-
ment this solution was approximately $3.7
million. Today, Reach 1 is well vegetated
and stable. Walking through the reach, it
is barely recognizable as a major CIP fl ood
and erosion control project.
Reach 7
In 2011 the City of Austin began
construction of stream stabilization for
Reach 7 in the lower portion of the water-
shed. Conditions were similar to Reach 1
in that yards, homes fences and utilities
were threatened due to severe and acceler-
ated erosion. This project was constructed
in two phases with each being approxi-
mately 500 feet in stream length. Similar
techniques were used for erosion control,
but a more natural looking type of stone
was utilized as compared to Reach 1. Also
instead of the wire forms used to construct
the soil lifts in Reach 1, temporary forms
were used that were removed upon com-
pletion. In the end this approach leaves
less manmade material in the creek and
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STREAMBANK STABILIZATION
20 September/October 2012
provides softer lines for the stabilization
facing. This project required integrating
two storm drain outfalls into the stabiliza-
tion and protecting two exposed wastewa-
ter crossings. At each of these crossings
the wastewater lines were stabilized with
rock grade control structures to prevent
undermining. Because this location is at
the lower end of the watershed and the
channel slope is much flatter, minimal
flood control benefits could be achieved
with this project. As the channel slope
becomes flatter, modifications to channel
geometry have a much smaller effect of
water surface elevation. Additionally, high
sediment loads delivered to the lower
reach would make channel modifications
unsustainable. The Reach 7 project was
designed with in-house engineers and con-
struction crews.
Reach 6
Th e third priority project in Fort
Branch will begin construction in the fall
of 2012 and continue through 2013. Th is
project includes 1,500 linear feet of stream
length using limestone boulder toe me-
chanically stabilized earth stabilization,
rock riprap grade control structures for
erosion control and replacement of a box
culvert with a 90 foot span bridge to reduce
roadway fl ooding. In this project the struc-
tural bank stabilization is limited to one
side of the channel and the opposite bank
is to be inclined to a stable slope and reveg-
etated. Th e fl ood control benefi ts include
nearly a 2-foot reduction in the 100-year
fl oodplain that currently makes local streets
a hazard during high fl ow events. Th e low
bid construction cost for the Reach 6 proj-
ect was approximately $2.5 million.
Summary
Th e Watershed Protection Depart-
ment has developed a multi-objective ap-
proach to watershed management and
stream stabilization that strives to maxi-
mize opportunities to achieve multiple
goals while minimizing adverse impacts
that have been associated with traditional
river engineering practices used in the past.
Focusing on accomplishing multiple goals
allows for better collaboration between
workgroups, better use of resources, and
more economically eff ective and environ-
mentally friendly projects. Although this
approach takes time and planning the ulti-
mate success of this integrated, reach-based
approach proves to be worth the additional
eff ort. L&W
by Morgan Byars, P.E. & Janna Renfro, P.E.
For more information contact Morgan Byars, P.E., Supervising Engineer, [email protected], (512)974-9790 or Janna Renfro, P.E., En gineer B, [email protected]. Th ey are both with the City of Austin Watershed Protection Depart-ment, Sustainable Stormwater Solutions Sec-tion, 505 Barton Springs Road, Austin, Texas 78704.
Acknowledgements: Th e City of Aus-
tin Watershed Protection Department
would like to acknowledge Eric Stewart,
P.E. with HDR Engineering, Inc. in Aus-
tin, Texas for assistance with design of the
Reach 1 and Reach 6 projects.
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