Project Case Study: Wetlands mitigation fights flooding

April 2007 » Feature Articles
Wetlands restoration reduced flood risks and restored wildlife habitats surrounding an historic Revolutionary War site.
JoAnne Castagna, Ed.D.

Project
Finderne Wetlands Mitigation, Somerset County, N.J.
Civil engineer
U.S. Army Corps of Engineers
Project summary
Wetlands restoration reduces flood risks and restores wildlife habitats surrounding an historic Revolutionary War site.

 

Federal-state collaboration helps restore and enhance an historic property

In 2000, the U.S. Army Corps of Engineers’ (Corps) New York District decided to collaborate with the state of New Jersey on a mitigation project that is enhancing and restoring the land around the historic Van Veghten House to create wildlife habitats and a public park. The Corps’ Finderne Wetlands Mitigation project is part of the Green Brook project designed to reduce flood damage in the Raritan River Basin in north-central New Jersey. The project is located on 130 acres of land along the Raritan River in Bridgewater Township, Somerset County.

The banks of an 800-foot-long stream on the project site that flows into the Raritan River were contoured to prepare for planting willow trees.
Photo: Mike Breslin

According to Megan Grubb, biologist and coordinator, New York District, U.S. Army Corps of Engineers, the wetland mitigation work is satisfying the mitigation requirements that the Corps has with all of its flood damage reduction projects. "The project is enhancing existing wetlands, forested land, and grassland habitats on the site and creating 20+ acres of man-made wetlands to sustain wildlife and create an educational public park." said Grubb.

The land was used for farming crops and livestock from the late 1600s to just a few years ago when Somerset County purchased it for open space preservation and park development. Years of farming had caused erosion problems on the land. One of these farms is the historic Van Veghten House. By 1699, the Van Veghten family farmed a large tract of land that included all of the property now under construction at the mitigation site. An 18th century, red brick Dutch farmhouse still stands on the bluff above the floodplain with a view to the Raritan River. The house, presently occupied by the Somerset County Historical Society, has a rich history that includes sheltering General George Washington’s Quartermaster General, Nathaniel Greene, during the Revolutionary War, while his soldiers camped nearby.

According to Grubb, the Corps has been working cooperatively since 2000 with the county’s Parks Commission to plan, design, and construct the site. Construction finally began in January 2006 when the land was graded to prepare it for spring seeding. Grading sets the stage of the mitigation work by achieving a soil elevation that supports the water requirements for wetland plant growth. The soil in the wetland creation areas was then tilled using a 30-inch plow-bedding harrow to create mounds and depressions, mimicking the uneven surface of a natural wetland. The soil was then fertilized and limed and nearly 100,000 trees and shrubs were planted. Habitat mitigation areas were also seeded with a mixture of native grasses and wild flowers.

Several wetlands, forested lands, and grasslands were enhanced or created to provide nesting and foraging habitats for a variety of birds, amphibians, reptiles, aquatic invertebrates, butterflies, and mammals. The public will be able to view these habitats by walking along a 2-mile nature trail created by the Corps. Signs along the trail educate hikers about the habitats and the wildlife they support, as well as provide facts about the nearby Van Veghten House. Also on the site are two recreation fields with parking lots and access roads, making the site a part of the Raritan River Greenway."Most of the mitigation work was completed in the summer of 2006. Twelve acres of recreational area, such as the trail and playing fields, will be opened to the public in the spring of 2007 after the grasses and plants have had a chance to grow," added Grubb.

A multi-section, pre-cast concrete arch bridge with a natural bottom replaced an undersized pipe culvert.
Photo: Mike Breslin

Habitat enhancement
The Finderne Wetlands Mitigation project included construction of or enhancement to the following wildlife habitats:

Forested wetland (enhanced)—This is wetland that has deciduous woody vegetation with a tree canopy taller than 20 feet. Approximately 14 acres of existing forested wetland were enhanced by planting trees, such as oak, ash, and sycamore; and shrubs, including summersweet, silky dogwood, and high bush blueberry.

Forested wetland (constructed)—Twenty-one acres of pastureland was turned into forested wetland. The land was graded, then seeded with a mix of wetland plants and floodplain grasses, and planted with bare-root and container plant material. Trees planted included oaks, ash, and sycamore; shrubs planted included summersweet, silky dogwood, and high bush blueberry. In some areas, the land was graded to create vernal pools—ephemeral spring ponding areas used by salamanders, invertebrates, and frogs for breeding.

Scrub-shrub wetland—This is a wetland that has primarily woody vegetation that is shorter than 20 feet. Approximately eight acres were enhanced by seeding and planting the wetland to make it more desirable for various wildlife species.

Emergent wetland (wet marsh)—Five acres were enhanced by seeding and planting the wetland to make it more desirable for various species of wildlife.

Riparian forest (corridor forest)—This is a forest that borders a river, in this case the Raritan River. Approximately 25 acres of riparian forest were restored by seeding and planting. In addition, the riparian buffer, a strip of woody vegetation along the river’s banks, was increased to 100 to 300 feet wide to create a habitat for wildlife that thrives in this type of environment, including species of birds, mammals, reptiles, and amphibians. In addition, the larger buffer sustains shade cover for fish habitats within the river. In this buffer area, various shrubs and trees were planted, including shrubs, such as elderberry, spicebush, and black haw viburnum; and trees such as hickory and silver maple. These trees were selected because their shaggy bark at maturity could provide a suitable roosting habitat for bats during the summertime.

Stream—An 800-foot-long stream, referred to as the Finderne Brook, runs through portions of the site. The stream was eroding and the Corps took steps to create a more natural water flow and to restore its habitat. To improve the water flow, the floodplain was widened to prevent the stream’s banks from eroding, and an undersized pipe culvert that was constricting flow was replaced with a natural-bottom, arched culvert bridge. To improve the stream habitat and stabilize the banks, the stream was graded, seeded with floodplain grass, planted with wetland plant cuttings such as willow species, and covered with a degradable coir matting to stabilize riverbank soils until vegetation takes hold. In addition, to prevent soil erosion, supplemental riverbed stone material was placed in the stream. The stones also create a series of pools and riffles for fish and invertebrate habitats, such as crayfish and pickerel frogs, which have already been sighted in the stream.

Grassland—Thirty-nine acres of enhanced grassland has transformed the property around the Van Veghten House that overlooks the Raritan River. The grassland provides house visitors an unobstructed view of the vista across the floodplain toward the Raritan River. The floodplain was seeded with warm-season grasses, including Indian grass and bluestem; and wildflowers, such as ox-eye daisy, asters, and coreopsis; that will support a population of pollinating birds and insects. The meadow will be a foraging area for the resident fox and red-tailed hawk, as well as for other birds and small mammals.


JoAnne Castagna, Ed.D., is a technical writer for the U.S. Army Corps of Engineers, New York District. She can be contacted at joanne.castagna@usace.army.mil.

Mitigation advice
Megan Grubb, biologist and coordinator for the New York District, U.S. Army Corps of Engineers (Corps), offers the following suggestions for conducting a stream a mitigation project:

  • Contact plant nurseries early to find out what species are available and whether you can get the quantity and plant size needed for the project.
  • Plan ahead when using native plants. If you plan to grow native species in your project using seeds and cuttings collected directly from the area, initiate propagation activities at least two years prior to project construction.
  • If practical, plan for storing large quantities of plant material on the site, especially bare-root trees and shrubs. The Corps’ construction contractor used an on-site refrigerator truck for plant storage. The truck, which mimics a greenhouse by maintaining temperature and humidity levels similar to a nursery, allows storage of large quantities of plants and extends the window of time cuttings can be stored on site for planting. Without the truck, storing and planting bare-root material would have been limited to just one to two days for each delivery of plants. The truck also preserved live stake material in its dormant state for a period that extended beyond nursery availability.
  • Have project designers make repeated site visits during the design process because site conditions can change. Incorporating any necessary design changes prior to construction helps minimize construction time delays and costly modifications. Designers should also be involved team members during the construction process.
  • Collaborate with property stakeholders. For example, the Corps reached an agreement with the State Historic Preservation Office to plant grassland rather then trees near the Van Veghten House to maintain the historic view from the house to the Raritan River. The Corps also reached an agreement with a local utility to plant unobstructive vegetation in areas of the site to provide continued access to overhead power lines.

Grubb said that the success of the Finderne Wetlands mitigation project has encouraged her to seek out other sites in the area to perform similar work. "We are already observing wildlife on the site, including red tail hawks, great blue herons, painted turtles, northern water snakes, freshwater clams, and a resident red fox."


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