Awcomin Marsh had been diked and used as a spoil disposal site for the dredging of Rye
Harbor in the early 1940's and again in the early 1960's. Approximately twelve acres of
this site has been restored by breaching dikes and digging ditches to replace the original
tidal creeks filled by spoil. Monitoring indicates a reduction in the invasive plant
The photos to the right show ditching done to restore the first twelve
acres (Phase 1). Currently, Phase I is complete and Spartina alterniflora and
other native species are regenerating.
Phase II was completed during the winter of 2003, which included
removing the dredge spoil from 25 acres of salt marsh.
At some time during the early 1970's, flashboards were installed in the Beards Creek culvert under
Route 108 in Durham.
This impounded the creek and blocked tidal flow upstream. The result was a loss of approximately 16
acres of salt marsh. Restoration of the former salt marsh will require removing
the flashboards and installing a larger culvert at Coe Drive upstream of Route 108.
The sewer line that crosses the creek
system off Route 108 will have to be stabilized if the
flashboards are removed and the pond emptied. This
project is in the early planning stage. Several issues will have to be resolved for this
project to go forward these include a change in the aesthetics of
pond to a salt marsh, concerns about loss of the
crosses Beards Creek several hundred feet
upstream of Route 108. This site was being used in the
Envirothon as a special problem potential mitigation site.
The tidal restriction at Brown's River was along an inactive railroad line at the boundary between Seabrook
and Hampton Falls, New Hampshire.
The 48" culvert
originally installed by the railroad was too small and the invert (bottom) too high to
allow adequate tidal flow to approximately 41 acres of marsh. The restrictive
culvert is located on the property of the Seabrook Nuclear Power Station.
above shows the old 48" culvert.
This picture was taken from the downstream side of the railroad embankment.
that the water in the pipe is higher than the water in the creek indicates that the
embankment is acting as a restriction to tidal flow. The railroad line is
presently inactive and some of the track has been removed.
The project has been designed and funded, and is currently in the
planning phase. The plan is to replace the current culverts with a
precast 5' x 7' culvert.
The photograph above right is looking upstream from the railroad
embankment. The periphery of the marsh is degrading as evidenced by the stand of
Phragmites in the distance.
The Little River Salt Marsh is a back barrier marsh lying between
Little Boars Head in North Hampton and a rocky headland just south of North Shore
road in Hampton. A USDA
Soil Survey indicated that originally the marsh was approximately
193 acres in size. By the 1990's most of the original marsh had deteriorated
due to severely restricted tidal flow to the
The lack of an adequate connection with the ocean had also
caused serious flooding problems because storm flows from the Little River did not
stable a outlet from the marsh. The restrictive culvert did not allow
for either adequate tidal flow into the marsh, or adequate drainage off
the marsh after heavy rains.
Currently, almost the entire marsh has adequate tidal
flow restored and this project has state and national awards.
A storm in the fall of 1996 washed out a culvert
which restricted tidal flow to Meadow Pond, a highly degraded salt marsh. The
town of Hampton replaced this culvert with 24 foot concrete arch culvert. This new
culvert restores adequate tidal flow to approximately 117 acres of degraded salt marsh.
The photo shows a stand of the invasive plant Phragmites that was killed
after restoration of tidal flow.
Park, Rye, NH
a parking lot and boat ramp were constructed at Odiorne State Park.
They were built on approximately 0.5 acres of salt marsh. In 1988 the parking lot
was expanded toward Route 1A on upland adjacent to the original parking lot.
The photo shows the boat ramp and kiosk for collecting park admissions.
Park visitors using the parking lot for beach access
are forced to cross the salt marsh to get to the beach trail.
This salt marsh restoration project is in the early planning
stage, was used in the 2000 NH
Envirothon as a special problem potential mitigation site.
The Parson's Creek project
involved replacing several road culverts, and installing ditches to restore
adequate tidal flow to approximately 150 acres of marsh. In the fall
and winter of 1997-98, twin 6' x 12' concrete box culverts were installed under
Wallis Road along with associated ditching and ditch cleaning. A 5'
x 7' culvert was installed under Marsh Road
and the eroding bank of Parson's Creek was stabilized at
Concord Point. In the spring of 1999, the third culvert was installed under
Route 1A near Wallis Sands to complete the project.
The top left photo shows the natural outlet to the Parsons Creek Marsh at Concord
Point in Rye, photographed in 1997 before the installation of the Wallace
This second picture
(top right) was taken during the summer of 1999, two growing seasons
following restoration of adequate tidal flow. The channel is being cut deeper and
narrower (hence the exposed mud flat to the left). The reason for this is that the
tidal creeks in this area of the marsh had become wide and shallow because of lower flows
and a softening of the marsh surface (peat degradation). Increased flows are causing
the tidal creek to cut narrower and deeper as indicated by the deeper channel to the
right. The width and depth of the new channel is comparable to natural tidal creeks
in marshes of this size and watershed.
The third photo shows dead narrow leaf cattails killed by
increased tidal rapidly deteriorating due
to lack of tidal flow. Right is a shot of
alterniflora (light green) that has naturally revegetated "rotten
panne" following restoration of tidal flow. We have had to do almost no
planting of Spartina spp. in New Hampshire restorations because of the tremendous
A new culvert was installed under Marsh
Road in 1998 to replaced an 18" metal culvert that was no longer functioning.
Essentially, all tidal flow had been blocked to approximately 4 acres of marsh north of
Marsh Road. This area of the marsh was almost totally degraded (photo to
right) to 100% narrow leaf cattail.
Creek - Wallis Road, Rye, NH
new culvert was installed during the winter if 1998 - 1999 under Wallis Road, which was one of the main obstructions to tidal
flow in the Parson's Creek Marsh. The red arrow in the photo at top
shows the location of original culvert. The new culverts were
installed in the foreground away from the buildings at the edge of the marsh.
Engineering surveys and hydrology studies indicated the
need for the installation of twin 12 foot concrete box culverts.
are precast, and delivered by truck and installed in sections by a large crane.
Because the new culverts are
approximately 200 feet down the street
The photo on the left shows a father and son using the new
tidal creek for canoeing. Recreation is also one of the benefits of
restored salt marshes!
Creek - Wallis Sands, Rye, NH
project involved replacing the original 18 inch concrete pipe culvert
under Route 1A just south of the Wallis Sands State Park. The installation of a
new 5' x 7' concrete box culvert
in April of 1999 (photos, right) took about three days, from digging the ditch to repaving.
The enlarged culvert at Wallis Sands allows increased flow to the portion
of the marsh that feeds this culvert. This culvert in concert with the
new culvert at Wallis Road will greatly increase tidal flow to the
degraded marsh south of the Wallis Sands parking lot.
A two acre portion of the
Rye Harbor salt marsh had been cut off from tidal flow by a road constructed from Harbor Road
to the public boat launch ramp. This area was also used as a spoil disposal area
during harbor dredging in the early 1960's. As a result the area was not only denied
tidal flow but approximately 1.5 feet of sediment covered the original marsh surface.
As typically happens in these circumstances the marsh was completely taken over by
invasive species, primarily Phragmites.
Photos to the top right show the the marsh completely taken over by the
invasive plant Phragmites, after removal of
Three inadequate road culverts which
restricted tidal flow to approximately 37 acres of degraded salt marsh were
replaced between 1994 and 1997. The first was an 18" culvert, under a private drive, replaced in 1994 with a 40"
squashed corrugated metal pipe. The second, a 40" corrugated pipe under Locke Road,
was replaced in 1995 with a 9' x 12' concrete box culvert. The third and last, an 18" corrugated metal pipe under U.S. Route 1A, was replaced by a 5' x 7' concrete box
culvert in the fall of 1996. During the spring of 1997 connecting ditches were dug to
restore tidal flow to critical portions of the marsh (photo, lower right). Note the use of planks to reduce damage to the salt marsh
surface and soil structure. Some existing ditches were also
cleaned of sediment. Spoil and rocks from from previous ditching was also removed from the
surface of the marsh.
Spartina alterniflora and Salicornia
spp. were already
reestablishing by 1998 (photo, right). In addition to the regrowth of native salt marsh plants there has been a
reduction of the invasive species Phragmites in the restored areas of the marsh.
While some Phragmites persists on the marsh fringe and may have to be chemically treated,
the reintrodution of tidal flow has reduced its height and vigor, and undoubtedly
prevented its further spread in the marsh.
Sandy Point, Stratham,
In 1994, volunteers
cleaned sediment and debris from a tidal creek and side ditches at the Visitors
Center of the Great Bay Estuarine Research Reserve. The photo to the right
shows a volunteer working at Sandy Point where plywood was
used to prevent damage to the marsh.
Additional ditches and control of invasive
species may be needed in the future and occasional maintenance of the ditches
due to sloughing of the degraded marsh surface. This problem will
probably be reduced in the future as the marsh stabilizes.
In the early 1960's, a wooden bridge along the Stuart Farm access road was replaced with an 18" tide-gated culvert.
This restricted tidal flow to an 12 acre tidal wetland. This resulted in a dramatic change
in vegetation from a Spartina dominated salt marsh to a fresh water marsh/shrub wetland.
In 1993, a large metal arch culvert was installed restoring tidal flow to the marsh. The
immediate result was a die off of many fresh water plants. Further monitoring indicates
that salt marsh vegetation is returning. Anadromous herring have also been seen in the