-------
With assistance from a 2004 U.S. Environmental
Protection Agency (EPA) Clean Water Act (CWA)
section 319 grant, PLC began a project to protect
the marsh. PLC's proposed method was to install
an ECS in the vicinity of the bridge. The ECS is
essentially a low weir designed to retain water in
the marsh during winter drawdown, while allowing
normal connectivity and function (e.g., navigation,
fish passage) during the rest of the year. The stone
and impervious geotextile membrane structure was
designed to key into the new bridge footings and
span the river in a downstream-facing arc. The con-
struction of the ECS occurred in conjunction with
the fall 2008 bridge replacement work (Figure 2).
The marsh now has a more natural water level
fluctuation, because the ECS prevents the marsh
from being drained when the lake level is lowered.
The DES Dam Bureau designed and assumed
ownership of the ECS, and it will also ensure that
routine inspection and maintenance is completed.
PLC contracted with an environmental consultant
to conduct baseline monitoring, as well as three
years of post-construction monitoring to assess the
response of the marsh ecology.
Results
Since installation of the ECS, marsh water levels
do not fall below the crest of the structure during
annual lake drawdown. The unnatural spring and
fall fluctuations that affected Lake Horace Marsh
have been eliminated. In assessing project suc-
cess, it is evident that the ECS created the more
natural water-level fluctuations necessary for marsh
restoration. However, biological marsh community
response cannot be fully evaluated in the short
term without great effort and expense. Therefore,
vegetation community assessments are being used
as a surrogate measure for biological community
health. The key performance targets focus on
whether the ECS effectively stabilized marsh levels
to allow the establishment of diverse vegetation
types suitable for forage and nursery zones, as well
as secure overwintering habitat for reptiles and
amphibians.
Changes detected at Lake Horace Marsh relative to
the 2006 baseline studies include increased aquatic
bed and deep marsh vegetation, and reduced open
Figure 2. Installation of the ecological control
structure (ECS) during winter 2008 lake drawdown.
water (see Figure 1). The 2010 vegetation map-
ping showed that both the aquatic bed/open water
and aquatic bed/emergent marsh cover types had
increased, along with increases in several emergent
species and decreases in open water in both the
aquatic and emergent plots. These findings are
consistent with the more stable winter water levels,
resulting in a more suitable environment for over-
wintering perennial vegetation. Visually, the marsh
now appears as a narrow channel of predominantly
open water bordered by a mix of submerged aquat-
ics and emergent vegetation. The development of
diverse vegetative cover types is expected to con-
tinue as the substrates slowly accrete and perennial
vegetation expands.
Partners and Funding
Numerous project partners were involved in
completing this project. EPA provided $64,359 in
CWA section 319 funds. PLC, in close cooperation
with DES staff, coordinated the project. The DES
Dam Bureau provided designs and construction
oversight. The Weare Conservation Commission
provided $4,364 and the Russell Piscataquog River
Watershed Foundation provided $8,500. The F&GD
provided funding ($23,500) and technical assis-
tance. Individual PLC members donated $300 to the
project. Volunteers contributed an additional $6,179
of in-kind support to the nonfederal share for this
project, bringing the match to 40 percent of project
costs. The total project cost was $107,202.
UJ
O
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-15-001L
March 2015
For additional information contact:
Steve Landry
Merrimack Watershed Supervisor
New Hampshire Department of Environmental Services
603-271-2969 • Stephen.Landry@des.nh.gov
------- |