Restore America’s Estuaries 4th National
Conference on Coastal and Estuarine Habitat
Rhode Island Convention Center, Providence,
October 11-15, 2008
Field Session 12: Coastal Barrier Ecosystem
Restoration Along Rhode Island's Salt Pond
October 12, 2008: 8:30 am - 4:00 pm
Hosted by Coastal Resources Management
Council, The Nature Conservancy, Salt Ponds
Coalition, US Army Corps of Engineers,
Special thanks to Ocean House Marina
The south shore of Rhode Island from Point Judith in Narragansett to Watch Hill in
Westerly is dotted with coastal lagoons, colloquially termed “salt ponds”. The salt ponds
are extremely important habitat for fish and wildlife. Though highly productive, the
ponds are subjected to stresses ranging from anthropogenic nutrient loading from
increased development to rising water temperatures due to global warming. There is a
strong local interest in preserving and restoring habitat and resources within the salt
ponds. The Coastal Resources Management Council developed a Salt Ponds Region
Special Area Management Plan in 1984 (updated in 1999). Management goals include
preservation and enhancement of the diversity and abundance of fish, shellfish, and
waterfowl; restoration of barrier beaches, salt marshes, and fish and wildlife habitats
damaged by past construction or present use; and prevention of further degradation of the
natural system by over-development. The RI Department of Environmental Management,
the University of Rhode Island and local volunteers through the Salt Ponds Coalition (a
non-profit volunteer organization, see: http://www.saltpondscoalition.org/) have
monitored water quality and habitat of the salt ponds over the years.
The South Coast Habitat Restoration Project was initiated in 1997. The project goals
were to restore 57 acres of eelgrass (Zostera marina) in the three largest coastal ponds,
Ninigret, Quonochontaug and Winnapaug in Charlestown and Westerly, RI. Eelgrass
restoration is a high priority both from a local and national perspective. Eelgrass is
classified as a Special Aquatic Site in the federal Clean Water Act. The restored eelgrass
beds will serve as nursery areas for many important recreational and commercial fisheries
species, including bay scallop and winter flounder. It provides a critical substrate for
epiphytic communities. Eelgrass acts as a filter of coastal waters, utilizing nutrients and
causing suspended sediment to settle. It provides a food sources for higher trophic
Historically, the breachways into the salt ponds were mobile features. In other words, the
inlets would cut through the narrow barriers at different locations at different times. The
inlets also opened and closed as a result of coastal storms. When a large storm plugged a
breachway with sand, the local people would open it up again, digging with shovels or,
In 1952 the State of Rhode Island widened and deepened the natural tidal inlet to Ninigret
Pond to create the Charlestown Breachway. Stone jetties were constructed along the sides
of the breachway, in order to keep the inlet open for navigation. The jetties largely did
their job, but as a consequence, significantly increased the amount of sand that entered
the ponds from the ocean. The flood tides that rushed through the inlet pushed sand
grains along the breachway floor. When the water velocity decreased as it entered the salt
pond, sand was deposited in a tidal delta. Studies show a marked acceleration in delta
growth since the construction of the Charlestown Breachway. As the delta expanded into
the pond, the formerly lush eelgrass beds that covered the pond bottom were buried under
rapidly accumulating sand deposits. Breachways were constructed into Winnapaug and
Quonochontaug Ponds in the mid 1950s and early 1960s with the same results.
Figure 1: RI South Shore salt ponds
RI South Coast Habitat Restoration Project Time Line:
• General Investigation: authorized in 1995
• Reconnaissance Study completed in 1997, determined that there were
opportunities for aquatic habitat restoration in the Salt Ponds Region.
• Feasibility study 1998-2002, to “determine the most technically and economically
feasible; and socially, environmentally, and culturally acceptable project to
restore aquatic habitat (eelgrass beds, shellfish beds and anadromous fish passage
to Ninigret, Winnapaug and Quonochontuag Ponds).”
• Habitat to be restored: Ninigret Pond, 40 acres of eelgrass habitat; Winnapaug
Pond, 12 acres of eelgrass habitat; Quonochontaug Pond, 5 acres of eelgrass
habitat; Cross Mills Pond, 20 acres of anadromous fish spawing habitat.
• Studies completed as part of the project:
o Winter flounder survey (RIDEM)
o Water quality and seagrass observations: baseline water quality data
including tss, dissolved inorganic nitrogen and phosphorus, chlorophyll-a,
and light attenuation, elevation and density for existing eelgrass beds
o Shellfish survey (RIDEM)
Figure 2: reopening the Ninigret Pond inlet after a coastal storm
o Shorebird survey (URI)
o Benthic studies (URI)
o Flood tidal shoal evolution study (URI)
o Sedimentation sampling (ENSR)
o Eelgrass assessment model (UNH)
o Grain size (USACE)
o Hydrodynamic studies (USACE)
o Beach dynamics (CRMC)
• Plans and Specifications for Ninigret Pond eelgrass restoration completed in 2003
• Ninigret Pond construction
o west basin – November 2004 to April 2005, November 2005 to April
o east basin – November 2007 to February 2008
• Ninigret Pond eelgrass seeding – October 2006
• Ninigret Pond eelgrass monitoring 2007 to 2010
Winnapaug Pond and Quonochontaug Pond restoration schedules are dependent on
availability of funds.
n area B
Figure 3: Nearing end of 2005 dredge window
Figure 4: Area A completed 2006
Project Planning Studies:
Water Quality and Eelgrass Measurements
Contractor: Rhode Island Sea Grant/Dr. Scott Nixon, Stephen Granger
Contact: Ben Allen
Water quality data and eelgrass abundance measurements were needed to select the
optimum sites for eelgrass restoration efforts.
Rhode Island Sea Grant took bi-weekly measurements of wind speed, wind direction,
temperature, salinity, dissolved oxygen, Chl a, total suspended solids, nutrients, water
clarity and eelgrass percent cover from April 1999 to September 1999. Monthly sampling
continued until February 2000.
Sampling stations coincide with the location of stations monitored during previous
research. In addition, a logging light meter was installed to take long-term measurements
of light attenuation through the water column. The eelgrass beds surrounding the tidal
deltas were surveyed using a percent cover method (Braun-Blanquet 1965). These maps
will be overlaid with bathymetry data from the Army Corps of Engineers to understand
how depth relates to eelgrass abundance.
Contractor: Army Corps of Engineers
Contact: Don Wood
A hydrodynamic model of the three coastal ponds was necessary to estimate the amount
of sand that would collect on the tidal deltas and where it would collect through the
channel/delta areas. The model was also be used to determine which dredging scenario
would be most effective at reducing the quantity of sand movement to the tidal deltas.
Tidal elevations were made at high spring tide conditions by the ACOE, although it was
pointed out at the technical team meeting that these conditions do not take wind
conditions into account. Wind conditions have been shown to increase tidal height by up
to 20cm in the ends of the basins.
Current measurements for Ninigret, Qounochontaug and Winnapaug Ponds inlets were
fast enough to move medium sized sand grains.
Bathymetric data for the hydrodynamic model and this data were collected in June 1998
using the SHOALS system. The SHOALS data was supplemented with other survey
analysis due to problems with light penetration. The model calibrations were reasonable.
However, the sediment transport through the tidal inlets underestimated the ground
Flood Shoal Elevation Analysis
Contractor: University of Rhode Island Department of Geology/Dr. Jon Boothroyd
Contact: Dr. Jon Boothroyd
The objective of the flood tidal delta elevation analysis was to provide sedimentation
rates calculated from photogrammetric analysis and to aid in predicting the response of
the delta-lobe morphology to various dredging scenarios.
Dr. Boothroyd and his associates produced maps for Winnapaug, Quonochontaug and
Ninigret Ponds using the 1995 orthophotos that are at a 1:3000 scale and show the delta
accumulation in periods of time. The volumes of sediment deposited are derived by
assuming a delta thickness of 1 meter for new lobes (based on past core data), multiplied
by the increase in area to give a volume increase.
The flood tidal delta grows by lobe accumulation. In Quonochontaug Pond, where water
depth is greater than in the other ponds, lobe growth is not as evident. In Winnapaug
Pond there is a high tidal range and more circulation so sand deposits further into the
pond. Ninigret Pond, which was dredged in 1985, showed a decrease in the expansion of
the active lobe; the total sediment area change went from an average of 8,642m2/year
over 1980-1985 to 1,909m2/year over 1985-1992.
Figure 5: Flood tidal delta accretion from 1939 to 1999 (1999 base aerial photo).
Contact: Chris Hatfield, ACOE
The objective of the sedimentation rate sampling was to define the sedimentation rate of
representative areas of the delta focusing on less or inactive delta areas to ensure that
these areas, once planted will not become active in response to channel and delta lobe
dredging or future storm events.
Depth of disturbance rods are used to periodically measure12 locations in Ninigret Pond,
8 locations in Winnapaug Pond and 7 locations in Quonochontaug Pond. Locations were
chosen to include all of the morphological variations of the delta that are likely to be
planted. The active lobe was also selected to measure a maximum sedimentation rate to
be expected for a new lobe if one were to become active (or reactivated) in response to
Sampling was done from June through November 1999.
Contractor: Dr. Fred Short, University of New Hampshire
Contact: Larry Oliver, ACOE
An eelgrass assessment was done to analyze current and historic eelgrass data from the
RI Salt Ponds to determine the best alternative for the dredging of the tidal shoals.
Historical data and field collection was used to help the ACOE determine which dredging
scenarios would result in the project goal to restore eelgrass to the tidal delta areas. A
site selection model was used to evaluate the conditions affecting eelgrass survival (i.e.,
sedimentation rates, depth and sediment composition), to display the incremental benefits
of various alternatives relative to supporting eelgrass. Also, an eelgrass growth model
that incorporates the major physical requirements of eelgrass growth into a computer
model was used to predict eelgrass growth with different environmental parameters
(related to different dredging scenarios).
Figure 6: Ninigret Pond Subaqueous Soils Textures showing 2006 eelgrass extent and
spawner sanctuary (hatched area).
Contact: Art Ganz, RIDEM Fish and Wildlife
Art Ganz of the RIDEM Fish and Wildlife completed surveys of the tidal deltas in
Ninigret, Quonochontaug and Winnapaug Ponds. The objective of the surveys was to
determine whether or not significant populations of bivalve mollusks had colonized the
delta formed by deposited sand immediately inside the ponds. Sampling stations were set
at randomly located sites around the tidal delta. Efforts were made to sample intertidal
areas, shallow subtidal areas and eelgrass beds adjacent to the breachway deltas of each
Shellfish mean densities were reported as follows:
Ninigret Pond Shellfish Mean Densities
Bay quahaug: 1.67/sq.m (range 0-7)
Surf Clam 0.38/sq.m (range 0-2)
Soft shell clam: 5.22/sq.m (range 0-38)
Razor clam 1.05/sq.m (range 0-10)
Quonochontaug Pond: Shellfish were practically absent along the breachway tidal delta.
Winnapaug Pond: Shellfish were practically absent throughout the study area.
Benthic Infauna Study
Contractor: Dr. Sheldon Pratt
Contact: Larry Oliver, ACOE
Understanding the benthic infauna (animals living on the substrate and in the soft bottom)
use of the tidal deltas is important for avoiding impacts to these species and the species
that forage on them.
Five core samples were taken in each pond at the subtidal portion of the delta and deep
areas where Zostera marina is present. Samples will be prepared for removal of
organisms through 2.0 and .5 mm sieves. Organisms will be identified to the species
level in most cases.
Contractor: Peter Paton, URI Department of Natural Resources
Contact: Larry Oliver, ACOE
The shorebird survey was necessary to assess shorebird use in the vicinity of the tidal
deltas. The U.S. Fish and Wildlife Service believed that the shoals at the entrance to
Ninigret Pond provide foraging areas for piping plovers (Charadrius milodus) and
roseate tern (Sterna dougallii), which are federally-listed threatened and endangered
species. URI performed avifauna surveys of inter-tidal portions of the flood tidal shoals
at Ninigret, Quonochontaug and Winnapaug Ponds. Surveys are conducted with the aid
of a spotting scope and specified observation points. Four one hour surveys per week
were conducted at each pond between August 4 and October 27, 1999 for a total of 48
surveys per pond. In addition, two weekly surveys shall be conducted during full moon
and spring low tides. Data indicates that over 49 species have been identified at all three
salt ponds. Piping plovers were detected at all three ponds and roseate terns were
detected at Quonochontaug and Ninigret Ponds.
Winter Flounder Larvae Sampling
Contact: Larry Oliver, ACOE
The salt ponds provide valuable habitat for Winter flounder (Pseudopleuronectes
americanus). Data collected over the years by the state RIDEM Division of Fish and
Wildlife and the academic community has not focused on the use of the tidal delta by
Winter flounder. This sampling effort supported the study by defining the use of winter
flounder larvae on the tidal delta. Sampling was performed using the epibenthic sled for
collecting demersal fish eggs described by Crawford and Carey (1985; Retention of
winter flounder larvae within a Rhode Island salt pond, Estuaries, Vol. 8, No. 2B, pages
217-227). Following is a brief summary of the survey data:
Ninigret Pond: No winter flounder eggs were found in the five samples taken on
the tidal flood shoal
Quonochontaug Pond: Two winter flounder eggs and four larvae were found in
the four samples taken on the tidal delta.
Winnapaug Pond: Five winter flounder eggs and three larvae were found in the
five samples taken on the tidal delta.
Results and Challenges
This project established a protocol for identifying optimum eelgrass transplant conditions
which can be applied to other restoration projects (Short, 2001). Once these parameters
were identified for Ninigret Pond, the subtidal portion of the flood tidal delta was
dredged to restore favorable conditions for the reestablishment of eelgrass beds. A
sediment catchment basin was dredged in the inlet to capture sediment before it entered
the salt pond. Sand that was dredged from the pond and the catchment basin was pumped
to the intertidal area of the adjacent beaches. This sand was transported on and along
shore by waves and currents to create storm resilient beaches. A portion of the salt pond
restoration area was seeded with eelgrass. Monitoring of both the seeded bed and the
unseeded habitat show eelgrass growth exceeded expectations in the first year. This
enabled the project partners to agree to use the funding targeted for more planting to be
used instead for dredging more habitat. The monitoring will be continued and some
additional seeding may be done in the eastern part of the salt pond.
The eelgrass is doing well in the habitat restoration area near the inlet where there is
exchange with the ocean waters. Other areas of Ninigret Pond have seen decreases or
total loss of eelgrass, particularly in the western basin where there is less tidal flushing.
The project was designed to restore eelgrass habitat in the section of the salt pond likely
to have better water quality. Recent research indicates that eelgrass is very sensitive to
water temperatures as well as water quality (Bintz et.al., 2003). Water temperatures are
anticipated to increase in the future, making this habitat area increasingly important.
The dynamic nature of the coastal barrier and salt pond environment continue to pose
challenges. The Army Corps of Engineers and the Coastal Resources Management
Council were able to work together on adaptive strategies throughout the construction
phase of the project in response to unanticipated events. However, the amount of
sediment transported into the pond far exceeds the model predictions. The anticipated
schedule for dredging the catchment basin was every seven to ten years. The initial basin
was no longer functioning after the first season. It was dredged and expanded in the
second dredge season. It is full again. Dredging the catchment basin is scheduled for
Beneficial Reuse of Sediment
The flood tidal deltas in the salt ponds are sediment sinks. In other words, sand that enters
the pond stays in the ponds. The amount of sediment entering the ponds accelerated after
the breachway construction (Figure 5). The beaches along Rhode Island’s south shore
have few sediment sources for replenishment. All the sand transported into the ponds is
sand removed from the longshore sediment transport system (predominately west to east).
During this project, more than 200,000 cubic yards of sediment were physically removed
from Ninigret Pond and pumped hydraulically back to the beaches Sediment was
discharged into the intertidal area where it moved along the shoreline creating wider,
more storm resilient beaches (Figure 7 ).
Figure 7: Beneficial reuse of dredge material.
Eelgrass Seeding and monitoring
Initial project appraisal determined that eelgrass growth in the vicinity of the flood tidal
shoals of Ninigret Pond was being altered due to shoal accretion. An optimal depth
model for eelgrass growth in Ninigret Pond was run during the feasibility phase of this
project to predict depths needed for eelgrass survival. Following the hydraulic dredging
of the sandy material from the shoals to the predicted optimal growth depth, various
methods to establish eelgrass were evaluated. These methods included whole plant
transplanting from donor beds, whole plant transplanting using mariculture raised plants,
and mechanical seeding of eelgrass seeds. Mechanical seeding was started in the
summer/fall of the year following dredging. To date, 2 acres of the dredged areas have
been mechanically seeded. Transplants of whole eelgrass plants and additional
mechanical seeding have been temporarily suspended as the area is experiencing natural
recruitment from adjacent eelgrass beds.
Eelgrass seeding was done with a system designed by researchers at the University of
Rhode Island Graduate School of Oceanography. The system is comprised of a boat-
pulled sled which deposits seeds below the sediment surface. Seeds are encased in a
Knox gelatin matrix. This prevents or reduces seed predation and loss of seeds from
waves and currents. Gelatin-encased seeds are injected into the sediment from the sled
using a food processing pump similar to that which is used to make jelly donuts. A metal
flange mounted on the back of the sled sweeps sediment over the furrows created by the
pump, covering seeds with an inch of sediment
Figure 8: eelgrass seeding using a specialized sled designed by URI researchers.
Monitoring of the project area occurs annually. Monitoring consists of: 1)
quantitative assessments of SAV and macroalgal species in the portion of the project area
that was seeded mechanically; and 2) qualitative underwater video assessments of the
entire project area. Quantitative assessments include the identification of all SAV and
macroalgal species present and percent cover of all species within a 0.25 m2 quadrat.
Qualitative underwater video assessments of the project area assess present or absence of
Monitoring data from the Ninigret Pond Restoration Project. Quantitative Assessments
are based on data acquired by examining percent cover of eelgrass in a 0.25 m2 quadrat.
Qualitative assessments are based on random underwater video recordings.
Average Percent Cover
Seeded Area 18% 20%
Seeded Area 20% 50%
Number of Stations with SAV Present/Number of Stations
Shoal A 2/5 3/5
Shoal A 3/5 5/5
Shoal B Not Sampled 1/5