Section 319
NONPOINT SOORGE PROGRAM SOGGESS STORY
Stakeholders Cooperate to Stabilize River and Restore Habitat
\A/3t6rbody ImprOVGd Extensive sand and gravel extractions during a major
interstate highway construction project in the late 1970s led
to channel instability and habitat problems in an eight-mile segment of New Hampshire's
Pemigewasset River. As a result, the New Hampshire Department of Environmental
Services (NHDES) classified this segment of the river as impaired by a non-pollutant in
the 2004 Clean Water Act (CWA) section 305(b) report. In 2003 stakeholders launched a
geomorphology-based project that restored the stream channel and improved habitat.
Therefore, NHDES will not classify this river segment as impaired for aquatic life use by
flow regime alterations in the state's 2012 CWA section 305(b) report.
Problem
The Pemigewasset River (Figure 1) originates in
central New Hampshire's Franconia Notch State
Park and flows south through the White Mountains
until it merges with the Winnipesaukee River. In
the late 1970s, sand and gravel were excavated
from the river's active floodplain and used in
constructing Interstate 93 near Woodstock, New
Hampshire. The extraction created a 30-acre pit
area and a large pond with depths up to 30 feet.
The removal of floodplain materials caused the
river to jump its bank (a process known as an avul-
sion) during a period of heavy rain when the river
flow accessed the damaged floodplain. The river's
new course flowed through unconsolidated materi-
als and the pond.
After the avulsion, this reach of the Pemigewasset
River became excessively wide and shallow. It
continued to have channel instability issues, includ-
ing continuous bank erosion, channel widening,
formation of multiple channels and degradation
of the cold-water fishery. The integrity and habitat
of the pond were also compromised as high river
flows continued filling it with sediment. Surveys of
channel dimensions at six cross sections indicated
that the channel characteristics were such that the
river could not effectively transport the watershed's
flow and sediment volumes. Therefore, the reach
was assessed as non-supporting of aquatic life
use due to streambank destabilization, and NHDES
classified this segment of the Pemigewasset River
as impaired by a non-pollutant (Category 4C) in the
2004 CWA section 305(b) report.
Figure 1. A porous rock weir helps to stabilize the restored
section of the Pemigewasset River.
Project Highlights
In 2003 the Pemigewasset Chapter of Trout
Unlimited received a $14,038 CWA section 319
grant and began restoration planning. In 2006 the
Chapter received a second CWA section 319 grant
of $315,000 to finalize the construction design,
obtain permits and complete the restoration on a
2,200-foot reach of the Pemigewasset River. The
geomorphology-based project reconnected the
river to its original channel, reduced the impacts
associated with floodplain land loss, enhanced
the in-stream and off-river fisheries and waterfowl
habitat, and restored the impacted river reach to a
stable condition.
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Project partners corrected
the channel's alignment,
elevations, and dimensions
by using large boulders to
construct more than a mile of
cross-vanes and rock vanes,
adding targeted streambank
toe protection, and creating
more than 900 linear feet
of floodplain stabilization
structures (Figure 2). Project
partners planted more than
150 mature willow clumps and
more than 50 trees ranging
from one to five inches in
diameter. They also planted
wetland grasses, plants and
bushes in the new riparian areas. Project partners
created in-stream habitat by shaping the chan-
nel and adding features such as pools, glides and
riffles. These features not only provided immediate
habitat benefits but also support diverse recre-
ational opportunities that had been absent from this
reach since the avulsion occurred. Anglers, boaters
and swimmers now enjoy Whitewater, swimming
holes and improved fishing opportunities along this
restored reach of river.
Figure 2. Construction
contractors and the project's
fluvial geomorphologist used
heavy equipment to construct
in-stream features.
Results
Members of Trout Unlimited, with technical assis-
tance from the project's consulting team, monitor
channel cross-section dimensions (cross-sectional
area, bankfull width, and bankfull depth) as the
prime indices of channel stability. To assess the
stability of the restored stream reach to determine
whether it supports the designated use for aquatic
life, DBS reviewed geomorphic survey data collect-
ed in 2011. Analysis confirms that, despite signifi-
cant destruction of transplanted riparian vegetation
by beavers and record flood flows experienced
in the fall of 2011, the geomorphic indices in the
project area continue to remain within acceptable
ranges and are considered stable (Figure 3). The
stream reach now provides physical conditions
supportive of the aquatic life designated use. On
the basis of these data, NHDES will not classify the
river segment as impaired for aquatic life use by
flow regime alterations in the state's 2012 CWA sec-
tion 305(b) report. Pemigewasset River assessment
unit NHRIV700010203-01 remains on the CWA sec-
tion 303(d) list of impaired waters due to aluminum,
pH and mercury.
Pemigewasset River Restoration Project-Supplemental Report
XS14-XSAreavs NH Reg. Hyd.Geom. Curves-provisional
XSArea(sqft)
LN [Predicted]
67%UpperCI(+lSE)
67% Lower CI(-ISE)
95%UpperCI(+2SE)
95%LowerCI(-2SE)
XS14
2.50 3.00 3.50 4.00 4.50
LN [Drainage Area (sq.mi.)]
Figure 3. A regional hydrologic geometry curve shows how
pre-project (2004) and post-project (2011) stream channel
measurements for cross section 14 (black squares) compare to
predicted stable channel condition dimensions (includes area
between the upper and lower confidence intervals). Data show
that the restored segment falls within the upper confidence
interval, indicating that it maintains stable channel dimensions.
Similar graphs were analyzed for multiple cross sections and
stability indicator metrics.
Partners and Funding
Numerous partners cooperated on the project,
including Trout Unlimited, New Hampshire Fish
and Game Department, Horizons Engineering, the
Chase family, NHDES and the U.S. Environmental
Protection Agency (EPA). EPA CWA section 319
funds provided $14,038 for the initial study and
$315,000 to administer, plan, document and imple-
ment the restoration. Trout Unlimited provided proj-
ect coordination in close cooperation with NHDES
staff. Additional grant funding was provided by The
New Hampshire Conservation Committee ($47,500)
and the Davis Conservation Foundation ($10,000).
The New Hampshire Fish and Game Department
contributed $52,000, as well as additional techni-
cal support, and an abutting landowner donated
$260,000 worth of materials such as gravel, cobble,
wetland grasses, bushes and trees.
UJ
O
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-12-00100
September 2012
For additional information contact:
Barbara McMillan
Watershed Outreach Coordinator
New Hampshire Department of Environmental Services
603-271-7889 • Barbara.mcmillan@des.nh.gov
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