In the spring of 1994, the Franklin County Commission (now the Franklin Regional Council of
Governments) convened the stakeholders to encourage a cooperative approach to assessing and mitigating the erosion in the Turners Falls Power Pool. The Connecticut River Streambank Erosion Committee (CRSEC) was formed and its membership is comprised of local officials, state and federal agencies, non-profit environmental groups, landowners, and utility representatives. This time, the stakeholders reached consensus and the utility prepared a Draft Environmental Impact Report which described a bank project that would stabilize several thousand feet of eroding riverbank using bioengineering techniques. The necessary environmental permits were secured and the utility committed $1.2 million over six years toward what would be called Phase I of the bank stabilization work.
Goals for Bioengineering Projects
The long-term goals for the bioengineering bank stabilization projects
||Reduce erosion in the Turners Falls Power Pool and thereby reduce a source of non-point pollution (sediment) to the Connecticut River;
||Stabilize eroded riverbank;
||Enhance habitat value by reintroducing native plant communities;
||Protect private property and prime agricultural land that abut the River;
||Identify successful bioengineering techniques.
Additional Funding for the Bioengineering Bank Stabilization Project
The Franklin Regional Council of Governments
(FRCOG) was awarded $142,000 from the s.319 Non-point Source Competitive
Grant Program in order to monitor, document and report on three
of the sites to be restored under Phase I, to staff the CRSEC,
and to provide partial funding for construction of one of the
sites. The purpose of Phase I was to demonstrate the feasibility
and effectiveness of using various bioengineering techniques,
an innovative, "soft" alternative to rip-rap, gabions, and other
traditional "hard" engineering solutions. Bioengineering techniques
incorporate woody and/or herbaceous plants and plant materials
to construct a living system of bank protection. Using bioengineering
to stabilize eroding banks has many advantages when compared to
traditional armored bank treatments, including: the restoration
and enhancement of wildlife habitat, the restoration of aesthetic
resource values and the compatibility of the treatment with on-site
environmental resources. The use of vegetation to stabilize banks
also provides a buffer that can reduce the pollutant and sediment
loading associated with overland runoff and flood flows. The June
1999 report prepared by the Franklin Regional Council of Governments
for the s.319 grant describes the work completed at three Phase
I sites (link
). A total of 2,250 linear feet of eroding riverbank
In April 2000, the FRCOG was awarded a second
s.319 grant for Phase II of the Connecticut River bioengineering
restoration work and in March 2004, the FRCOG received a third
s.319 grant for Phase III work. The details of the projects, including
site selection, construction and monitoring, and technology transfer,
are described in the Final Reports (link
). These projects, like the Phase I project, were
a cooperative effort between the Franklin Regional Council of
Governments, the members of the Connecticut River Streambank Erosion
Committee, and Northeast Utilities (now FirstLight Power Resources,
Summary of s.319 - Funded Bioengineering Site Designs
Three sites were
restored under Phase I: Wickey, Shearer and Crooker. Construction
at the Crooker site was partially funded with money from s.319 grant
96-03/319. Although s.319 funding was used for the construction
of only one site, the final project report evaluated the design
and construction of all three sites. Vegetation and habitat monitoring
was performed at all three sites. The three bioengineering treatment
types used on the Phase I sites included:
Sand or gravel fill was placed in the undercut/scour zone and then covered with rock rip-rap. Coir fascines were placed in vertical layers above the rock toe and cabled in place. The area above the coir fascines was protected by burlap or coir fabric and then planted with live stakes of woody species.
This treatment was designed to be built at the mean water level and includes a rock toe and coir roll or fascine at the water’s edge. A flat area was created behind the toe and a pre-vegetated mattress was staked in place. The specified plants were designed to create an emergent wetland community. A gradual slope leads to the top of the bank. The upper slope was protected with coir fabric or burlap and seeded or planted with live stakes.
Sand or gravel was used to fill the undercut/scour zone. A rock toe was constructed and coir fascines were placed above the toe. Fabric-wrapped geogrid lifts were placed in layers above the coir fascines to construct the new bank. Dormant live brush was placed in-between the layers.
The construction of one site, known as the
Urgiel Upstream site, was partially funded by the Phase II grant
(00-04/319). The bioengineering design for this site was significantly
different from the design techniques used for the Phase I sites.
The Urgiel Upstream design used four bank treatment types:
Area was seeded with native seed mix and planted
with Red Oak, Red Maple and Sycamore trees, 4”-5”dbh, and Gray Birch,
Quaking Aspen, Pin Oak, White Ash and Cottonwood trees, 4 to 5 feet
Area was seeded with native seed mix and planted with
1 gallon pot-sized woody vegetation, including: Arrow-wood, Staghorn
Sumac, Gray Dogwood, Shadblow, American Hazelnut, Black Chokeberry
Area was seeded with native seed mix and planted
with 1 gallon pot-sized woody vegetation, including: Speckled Alder
and Silky Dogwood.
Area was planted with tubelings (rooted cuttings)
of Pussy Willow, Purple-osier willow, and Sandbar willow.
The Urgiel design incorporated several new techniques that had not been previously used in this reach of the Connecticut River, including:
||Planting willow tubelings in the stone toe to "soften" the appearance of the stone;
||Reducing the size of the rocks used in the stone toe to 4 to 6-inch diameter stone;
||Installing an erosion control blanket that would biodegrade more quickly;
||Simplifying bank reconstruction and revegetation by grading the cleared bank to a 1.5:1 slope and using hand techniques and installation to plant native herbaceous and woody vegetation. Geogrid lifts, brush mattresses and brush fascines used on the Phase I sites were not used at Urgiel.
The Phase III
site, known as Urgiel Downstream, is 980 feet in length. The bioengineering
design for this site is similar to the one used at the Phase II
site (Urgiel Upstream). The design has four bank treatment types,
like Urgiel Upstream, with the only difference being the addition
of a coir bio-log above the stone toe.
This design change was made in response to problems encountered at the Phase II site. The interface between the upper elevation of the stone toe and the lower elevation of the vegetated bank bears the brunt of the erosive forces from the fluctuating water levels. The coir bio-log was added to strengthen this interface.
Beginning in 2010, the bank stabilization techniques changed dramatically, due in part to the findings and recommendations in the Fluvial Geomorphology Study of the Turners Falls Pool (November 2007) prepared by Field Geology Services for FirstLight Power(link to report
This study describes four types of bank erosion present in the Turners Falls Pool and discusses appropriate methods for bank stabilization in this reach of the Connecticut River, including the use of large woody debris (LWD) to preserve existing beaches and promote the development of new beaches by trapping fine sediment. These beaches help to dissipate the erosive forces of the river, including fluctuating water levels and boat wakes. According to the Field Geology Services report, bioengineering projects that place dense accumulations of wood on beach facescould potentially capture additional wood floating from upstream, accumulate sedimentby baffling currents, and protect the bank from further erosion. In addition, the report goes on to state that logs arranged as deflectors that are angled slightly upstreamcould turn river currents away from the bank when high flows pass over the logs,potentially providing more immediate bank protection before sediment accumulatesbetween the logs.
The first demonstration site using LWD was constructed in Gill, MA. Partial funding for the design, permitting and construction of this 1,745 foot long site was provided by an EPA Targeted Watershed Grant awarded to FRCOG and its project partners.(link to website
FirstLight Power provided funds for the remaining costs of the project.