Tidal Wetland Restoration
in Connecticut (Part 3)
(Part 1)
(Part 2)
Tidal Wetland Restoration
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HAMMOCK RIVER, CLINTON RESTORATION VIA TIDAL GATE MANAGEMENT
Upstream of Beach Park Road, on the Hammock River in Clinton, nearly 120 hectares (300 acres) of tidal wetlands, mostly salt marsh, have been drained for salt marsh haying and mosquito control purposes since the early part of this century (Fig. 6). Gradually the vegetation, dominated by high marsh plant communities, was replaced by Phragmites. Charles Roman, a graduate student at Connecticut College documented the environmental changes that had taken place by the early 1980s. His research demonstrated that the wetland surface had subsided at least 38 centimeters (15 inches) and, when all four tide gates were opened in the fall and winter months, the flooding depth and duration resembled that of the previously discussed Lost Lake case study. During the summer, the tide gates were closed to drain surface water from the marsh, thereby eliminating breeding habitat for the salt marsh mosquito. However, without daily tidal flow sediments accumulated quickly in the ditches, which in turn trapped rainwater, creating an ideal habitat for freshwater mosquitoes.
Fig. 6 Map of Hammock River marsh
A cooperative program was begun in 1985 between DEP and the Mosquito Control Unit to restore
the degraded wetlands by utilizing modern open marsh water management techniques. The plan was to
restore tidal flushing during the summer to the extent necessary to maximize the emergent vegetation
and minimize the conversion of salt marsh to open water (similar to the Lost Lake scenario). A single
tide gate was opened in the spring of 1985 and photo stations were established to measure the
replacement of Phragmites by native marsh grasses. Reference stakes were installed against which the reduction in the height
of Phragmites could be measured at the end of the growing season. In the fall of 1985, the height reduction of Phragmites was
one meter. During the next three years, the annual height reduction averaged 30 centimeters (one foot) (Click to See Figure.
7). By the fifth and sixth year, Phragmites stopped growing, dead shoots no longer persisted and the exposed peat was being
colonized by salt marsh grasses. Local residents reacted favorably to the restoration, remarking on the improving vistas and
the return of wildlife such as egrets and waterfowl.
By 1992, Phragmites was decreasing throughout the entire marsh but it was apparent that in all areas, especially that west of Meadow Road, extensive would persist. The next year, a second tide gate was opened to increase the area of marsh flooded, and monitoring stakes were again set out. In the summer of 1994, complaints were received with respect to backyard flooding. Interestingly, no complaints were received about the more extensive flooding during the winter, when all four gates were open. In order to continue this highly successful marsh restoration project, the DEP has received federal funding through the Department of Transportation's Intermodal Surface Transportation Efficiency Act to design and implement a flood protection program for several low-lying properties. To everyone's surprise, no significant mosquito breeding occurred during this restoration. This can be explained by the fact that tides flood nearly all of the marshland on a daily basis, which prevents breeding by the salt marsh mosquito.
The draining of the Hammock River marshes may have caused water quality problems in the river and adjacent Clinton Harbor (see accompanying sidebar). Studies have shown that restoring tidal flow can quickly reverse this problem. Restoration of water quality is probably critical to the health of the living resources in this area including the natural oysters beds that line the channel of the Hammonasset River.
This project illustrates how salt marsh restoration can be accomplished at very low cost and through the manual operation of tide gates. Gate adjustments or closures are only necessary in advance of major storm events, making manual operation easy and cost-effective. Manual gate operation is impractical at sites where low-lying properties would be regularly flooded. In those situations, automatic tide gates may be used in which a water level recorder monitors the height of the tide and triggers the gate to close when the water reaches a pre-determined flood level (Fig. 8). A non-electric gate system which uses one or more floats to sense water elevations was developed by Thomas Steinke, Conservation Director of the town of Fairfield.
 Fig. 8 Self-regulating tide gates. (R. Rozsa) (110K) | Marsh Draining Can Affect Water Quality Studies on Cape Cod and elsewhere have demonstrated that draining salt marsh peat can create several significant water quality problems. Pyrite or iron sulfide, a common soil mineral, produces sulfuric acid when exposed to oxygen. If the soil in question has limited buffering capacity, the pH value in drained marshes can decrease to values as low as 3 to 4. These altered soils are referred to as acid sulfate soils and one such site has been located in drained marsh in Fairfield. Following rainstorms, runoff from the marsh causes acidic conditions in tidal creeks. In addition, organic compounds in this leachate can consume oxygen, causing hypoxia or anoxia (lowering or complete depletion of oxygen in the water) which can cause fish kills. Reflooding the marsh usually corrects the water pollution problems caused by draining. |
Tide gate management programs are being used in Pine and Ash Creeks in Fairfield and Groton Long Point, in Groton. At the latter, the Groton Long Point Association manages the tide gates and closes them when a major storm is forecast. Examples of degraded salt marshes that have been restored through complete gate removal include: upper Farm River, East Haven; upper Branford River and Gigamoque Creek, Branford; and Indian River, Clinton.
MUMFORD COVE, GROTON BURIED AND EXCAVATED MARSH
In the 1950s, an earthen dike was built around a salt marsh located on the eastern shore of Mumford Cove, and sediments dredged from the cove were hydraulically pumped into the southern end of the marsh (Fig. 9). These sediments spread across the marsh in a northerly direction, and excess water returned to the cove via a sluiceway located in the northwest corner. Fill depths across this six hectare (15 acre) marsh ranged from 0.6 to 1.2 meters (two to four feet), elevations too high to be flooded by the tides. Phragmites became the dominant plant, and the ponding of rainwater produced large, uncontrollable broods of freshwater mosquitoes.
Fig. 9 Map of Mumford Cove (120K)
Restoration began as a DEP and Mosquito Control Unit partnership in the fall of 1989, when the overburden of dredged sediment in the northwest corner was excavated by a lightweight bulldozer and transported to the adjacent uplands. Creeks and ponds were recreated using lightweight excavators (Fig. 10). The following spring, the U.S. Fish & Wildlife Service, through its Partners for Wildlife Program, joined the effort and provided equipment and operators to assist in the restoration. Over the next four years, the remaining wetland was unearthed, tidal creeks restored and wildlife ponds constructed. No planting was done, but vegetation re-established itself through the natural transport of salt marsh plant seed by the tides. Dense beds of the submerged aquatic plant Ditch or Widgeon Grass (Ruppia maritima), an important waterfowl food plant, spontaneously established in several of the ponds.
 Fig. 10 A low-ground pressure excavator digging a creek during the restoration of a buried marsh (R. Rozsa) |  RESTORATION RULES OF THUMB
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June 21, 1997 / DEP's Tidal Wetland Restoration Program / webmaster@po.state.ct.us