|
Bioengineered Streambank Stabilization on Silver Bow Creek
April 1998
October 1999
Silver Bow
Montana
Butte |
 |
| Silver
Bow Creek Map |
|
Estimated Cost:
Implementation costs for constructing the three basic types and
eight variations of bioengineered treatments included toe material,
willow bundles, fabric, excavator time and incidentals. Cost for
incidental(s) included stakes, rebar, flags, micorrhizae, polymer,
long sleeve rubber gloves, hard-hats, steel toe boots, waders, goggles,
orange vests, rain gear and OSHA Certified Labor. Costs for travel,
lodging, per diem and oversight are not included in the following
breakdown.
An excavator and operator was used for five days to construct the
four-foot deep trenches into which the willow bundles were placed
at a cost of $6,000 plus $500 for mobilization (total $6,500). The
cost of labor for planting was included in the cost per bundle of
willows at $15. Therefore, the cost for planting 1,020 bundles for
the three types and variations of bioengineered treatments was $15,300.
A total of 32 biologs measuring 20 foot long and 16 inches in diameter
were installed at five locations at a cost of $14 per foot ($280/log)
for a total cost of $8,960. Erosion control fabric (COIR cf #7)
cost $245 per role (120 sq.yd.) and $21.32 per role for installation
(0.02 cents/sq. ft) for a total cost of $266.32 per roll. A total
of 8 rolls measuring 6.6 inches wide and 165 feet long were installed
for a total cost of $2,130.56.
Project Sponsor(s): Atlantic Richfield Company
Oversight Agency: U.S. Environmental Protection Agency
Project Partners: Project complexity dictated use of an
interdisciplinary team approach including experienced professionals
with expertise in civil and hydraulic engineering, hydrology, fluvial
geomorphology, ecology, botany, bioengineering, habitat restoration,
fisheries and other related disciplines. ESA Consultants Inc. under
contract to the Atlantic Richfield Company (ARCO) developed the
Work Plan, CDM Federal Programs Corporation, Inc. prepared depth
to ground water and growth media placement maps, R2 Consultants
Inc. produced the low flow channel design plan, Schaffer & Associates,
Inc. developed the interim revegetation design plans, installed
intensive vegetation treatment, conducted project oversight and
monitoring, R. E. Miller contracted the harvesting and preparation
of willows and Aquatic and Wetland Company designed and installed
the bioengineered bank stabilization treatments.
Reasons for Action: The habitat value of Silver Bow Creek
had been severely impacted due to mining activities at the Anaconda
Mine.
Objectives: Create a healthy, functioning riparian ecosystem
to compensate for impacts
History of Site: A portion of the Silver Bow Creek drainage
basin near Butte, Montana was the site of a remediation project
titled Lower Area One (LAO) Phase I, Segment II. Remediation included
removal of large quantities of tailings and underlying soils with
elevated metals concentrations. Clean fill material was imported
to construct a 200 to 400 foot wide floodplain and a low flow meandering
stream channel. Consequently, the project presented the need for:
1) creating a fully vegetated riparian floodplain corridor, 2) restoring
biological function using bioengineered bank stabilization treatments,
and 3) creating diverse fish and wildlife habitat.
Pre-Restoration Photos: No
Design Narrative: The newly configured channel extended
7,000 feet (1.325 mile) with 14,000 feet (2.65 miles) of riparian
corridor that was planted with native grass species, herbaceous
sedges and rushes, shrubs including willow (Salix spp.) and tree
plantings. The planform of the low flow channel was designed with
a sinuosity of 1.25 and typical stream gradients from 0.2% to 0.4%.
The constructed channel included a top width ranging between 30
and 45 feet, a bottom depth of 2.5 feet, 1.75:1 side slopes and
a capacity to transport 270 cfs before overbanking. Observation
and map analysis resulted in identification of 30 outside concave
curve banks and 30 point bars or inside convex curve banks. Each
curve was numbered beginning at the downstream project boundary.
Careful consideration was given to stabilization of the streambank
zone defined by the channel edge or bank toe, bank slope and floodplain
terrace associated with the reconstructed channel. Five native willow
species were identified for planting in the streambank zone based
on their phenology-morphology, environmental tolerances and production
characteristics (ARCO 1997). Three of the five species were known
to be abundant within the Silver Bow Creek floodplain valley including
Sandbar willow (Salix exigua), Booths willow (Salix boothii), and
Yellow willow, (Salix lutea) and harvest sites were selected accordingly.
Other willow species played a minor role and were not considered
in the monitoring results discussed below: Geyers willow (Salix
geyeriana), Pacific willow (Salix iasiandra), and Bebbs willow,
(Salix bebbiana).
Bioengineered Treatments. Bioengineered bank treatments were located
at 13 of the 30 outside concave bends. Three bioengineered designs
were prepared and implemented based on the high and low risk erosion
potential and named according to presence or absence of the material
placed at the toe of the bank slope (Supplement
1, pdf). Toe material was considered nonstructural/organic and
included wattling (live facines), brush layering (willow cuttings)
and biologs constructed from biodegradable coconut fibers. A plan
was developed to avoid subjecting the newly formed floodplain; riparian
corridor and channel to the erosive overbank flows of spring snowmelt
runoff and isolated storm events. An engineered diversion was located
immediately upstream of the project site to divert flow of 35 cfs
into an alternate channel in excess for a period of five years or
until the concave banks became stabilized with native plant (i.e.,
willow) root structure. The diversion channel was sized to convey
the runoff from the 10-year-24 hour storm event estimated at 477
cfs.
Construction Narrative: The initial work steps included
harvesting, bundling, handling, soaking and planting willows. The
project began by harvesting dormant willows during the early spring
of 1998 and planting progressed thereafter during April, May and
June.
Harvesting Willows. Small lightweight chain saws and heavy-duty
brush cutters worked well for harvesting large numbers of willow
stems in a short period. Once willows were cut near ground level,
they were gathered and piled at a convenient site for processing.
Bundling. Processing willows for ease of handling included forming
a bundle by gathering ten stems (plus or minus one inch in diameter).
Dead stems were not included in the bundles. One person held a bundle
of ten stems while a second person encircled the bundle with five
wraps of plastic wrap that is then easily torn off. This was repeated
for a second wrap. The bundles were placed in piles of ten, loaded
onto a covered trailer to keep out of the sun and prevent drying
and transported to a site for soaking in water.
Soaking. All willow bundles were placed in a pond and to the extent
possible, submerged for a minimum of three days or longer. Soaking
willows ensures that the vascular tissue and buds are super saturated
and results in dissolution and leaching of an anti-root hormone
located in the stems. After soaking, bundles were removed from the
pond, transported to the construction site, placed in the creek's
flowing water and planted the same day.
Wattling was used as the protective toe at five locations for a
total 680 feet. A brush layer toe was installed at three locations
for a total of 513 feet. A biolog toe was installed at five locations
for a total of 650 feet. Therefore, the total bioengineered treatment
length was 1,843 feet (0.35 mile).
An intensive vegetation treatment (IVT) was applied throughout
the remainder of the corridor and included planting mini willow
bundles, other shrubs and trees above the ordinary high water mark,
sedges and rushes from the water edge throughout the capillary zone,
and intra-seeding and hydromulching the remaining space. This treatment
was applied to the remaining 17 low risk erosion potential banks,
point bars and straight reaches (14,000' minus 1,843' equal 12,257').
Mini bundles of willow cuttings were inserted to the ground water
table after punching a three to four foot deep hole with a dibble
bar attached to the bucket of a rotating trackhoe. Three staggered
rows on one-foot centers were planted along the concave bends and
two staggered rows on one-foot centers were planted along the convex
bend point bars and straight reaches. Planting distance from the
water edge ranged between one foot and three foot. The number of
cuttings placed in each dibbled hole varied according to the diameter
of the cuttings and ranged between two and four.
Construction Photos:
Project Success: Second year monitoring indicated a highly
successful stabilization project based on absence of erosion, vegetation
survival, density, growth, and streambank stability. The design
objectives have been met. The concave, convex and straight reaches
of the streambanks are stable, riffle/run/pool habitat is present,
several species of fish have been observed, waterfowl have become
residents, deer have been migrating through the corridor and site
aesthetics are rapidly developing. In channel habitat types are
improving and maintaining themselves. Sediment is moving through
the system with no major bed aggradation or degradation. Riffles
have unearthed clean large gravel and cobble that are suitable for
spawning. Riparian structure and habitat is developing at a rapid
rate.
The Lower Area One, Phase I, Segment II should be an example project
of how traditional nonfunctional hard riprap stabilization approaches
can be replaced by biologically functional bioengineered approaches
to erosion and bank stabilization challenges. Information and understanding
gained from the variety of bioengineering designs used on this project
will be considered during potential future designs downstream of
Butte.
How was success determined? End of the first growing season
monitoring during October 1998 included photography and qualitative
observations. End of the second growing season monitoring during
October 1999 included measurements of willow survival, density,
and growth (Ave. and Max. height).
Willow Growth (Second Year) Average height and maximum height measurements
were made at six of the thirteen- banks treated with the three different
types of bioengineered treatments and their variations: wattle toe,
biolog toe and brush layer toe (Table 1).
Stem height was measured within each of three randomly selected
one-meter sections for each of six bank treatments for a total of
18 meters (Table 2). The amount of
growth was measured from the surface of the ground to the woody-growing
tip of the stem. Branches and leaves were not measured.
Average height ranged between 4.0 and 4.6 feet for an average of
4.2 feet by the end of the second growing season. An average 77
day growing season (range = 74 to 80 frost-free days) was used to
estimate the inches of growth per day for the two growing seasons.
Average growth per day ranged between 0.33 and 0.38 inches per day
or a little over one-third of an inch per day.
Maximum height for the fastest growing stems ranged between 6.8
and 8.6 feet in height and averaged 7.8 feet for the six banks measured
(Table 2). Therefore fast growing stem
growth for the two growing seasons ranged between 0.57 inches and
0.72 inches for an average growth rate of nearly two thirds of an
inch per day (0.65"). A number of stems achieved a height of
8.6 feet (103.2") that translates into a growth rate of 0.72
inches per day by the end of the second growing season (77 days
+ 77 days = 144 days). Average willow stem growth under the conditions
within the Silver Bow Creek valley on average grew one-third of
an inch each day over the two growing seasons and the fast growing
stems averaged nearly three-fourths inch per day. Although not evaluated,
it was assumed that the amount of stabilizing underground root growth
equaled the amount of above ground production.
Mortality/Survival Planting Density. Interest was expressed regarding
the number of willow stems planted per meter for the installed variations
of brush layering. Therefore three one-meter sections were randomly
selected within six of the treatment types (18 meters). The number
of live stems and dead stems were counted. The number of willow
stems planted per meter did not vary greatly for the six banks sampled.
Average number of stems surviving per meter at the end of the second
growing season within the six treatments was 16.3 or 64% of those
planted (Table 3). Average number of
dead stems counted was 9.3 (36%) suggesting that the average number
of willow stems planted per meter was 26.
Bank Stability-First Growing Season Successful stabilization was
judged by two criteria: 1) an unpredictable storm flow and 2) quantitative
measurements.
An estimated flow of 450 cfs occurred following a severe thunderstorm
on July 31,1998 or approximately three months after treatment implementation.
It was estimated that 300 cfs was diverted into the alternate channel
and 150 cfs remained in the new Silver Bow Creek channel. Minimal
erosion damage was observed and no repair work was required. Therefore,
it was concluded that the bioengineered treatments worked well at
the design flow capacity.
Quantitative measurements based on erosion, stem survival/mortality,
density, above and below ground growth suggested that each treatment
produced greater than satisfactory subsurface root structure and
above ground woody stem structure. Willow clumps could not be pulled
from the ground at the end of the first or second growing season.
No erosion was observed in the 17 concave bend areas treated with
IVT.
Although quantitative measurements were not taken, species differences
in willow phenology/morphology and production characteristics contributed
greatly to bank stabilization. Sandbar, Booths and Yellow willow
cuttings each formed roots within 10 to 15 days of planting. Banks
were well stabilized during the first growing season and improved
significantly by the end of the second growing season. It was assumed
that the amount of above ground growth was reflected in the amount
of below ground root growth. Biomass production was rated high when
compared to other members of the same lifeform. Observations suggested
that Booths and Yellow willow cuttings out performed Sandbar willow
in terms of short and long-term above ground vegetative production.
Therefore, Booths and Yellow willow cuttings can be highly recommended
for future stabilization projects scheduled for the Silver Bow Creek
valley
For more information on this project, contact:
Jay Windell
Aquatic and Wetland Company
9999 Weld County Rd. 25
Ft. Lupton, CO 80621
Phone: 303-442-4766
E-mail: jay@aquaticandwetland.com
URL: http://www.aquaticandwetland.com/
OR
Chuck Stilwell
ARCO
307 East Park Street, Suite 400
Anaconda, Mt. 59711
Available Documentation:
Table 1. Bank number, treatment type
and length
Table 2. Number of willow cuttings
planted per meter, and number and percent survival
Table 3. Willow cutting growth at end
of second growing season
Table 4. Cost per foot comparison of
bioengineered and riprap treatments. Costs assume completion of
bank shaping /grading; all treatments extend up the bank.
Submitted by:
Susan Cousins
Aquatic and Wetland Company
1830 17th Street, Suite 100
Boulder, CO 80302
Phone: 303-442-5770
Email: susan@aquaticandwetland.com
Date: August 23, 2000
|
