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Using a Bioengineering Approach

The Bioengineering Group, Inc

“A lake is the landscape’s most beautiful and expressive feature. It is earth’s eye; looking into which the beholder measures the depth of his own nature. The fluviatile trees next to the shore are the slender eyelashes which fringe it, and the wooded hills and cliffs around are its overhanging brows.”

-Henry David Thoreau, Walden

Situated in Concord, Massachusetts, Walden Pond State Reservation is a 333-acre natural area used primarily for recreation and literary inspiration. Surrounded by forest, Walden Pond is a 62-acre, 103-foot deep kettle hole that was formed over 12,000 years ago during the last Ice Age when a chunk of ice that had broken off from the glacier formed a depression in the landscape and then melted, leaving a pond behind. Since European settlement of this area, the landscape directly adjacent to Walden Pond has remained relatively unchanged.

In the mid-1800s, Walden Pond was surrounded by one of the few remaining woodland areas in a heavily farmed environment. In 1844, Ralph Waldo Emerson, a local Concord resident, purchased 14 acres of land on the northwestern side of the pond. His long-time friend, Henry David Thoreau, also a Concord resident, had been greatly inspired by Emerson’s 1836 essay, Nature, which proposed the then unique idea that each individual should seek a spiritually fulfilling relationship with the natural world. In a quest to immerse himself in an environment of tranquility and solace, as well as to pursue a career as a writer, Thoreau accepted an offer from Emerson to build a cabin on a small portion of his newly acquired land.

In March of 1845, Thoreau began planning and building his modest one-room house, taking residence from July of that year to September of 1847. During his two-year stay, Thoreau studied natural history, gardened, wrote in his journal, and drafted his first book, A Week on the Concord and Merrimack Rivers. By no means a hermit, Thoreau kept in close contact with village activities, and even hired himself out as a surveyor, at which time he completed the first accurate survey of Walden Pond.

After his experiment in simplicity had been completed, Thoreau gave the cabin to Emerson and returned once again to a civilized way of life. Over the next seven years, Thoreau revised his journal entries, which were recordings of his thoughts and encounters with nature and society during his two-year stay in the cabin, and in 1854 he published the classic, Walden. In 1862, at the age of 44, Thoreau died after a prolonged struggle with tuberculosis.

During his lifetime, it had been a strong belief of Thoreau’s that “each town should have a park…a common possession forever, for instruction and recreation”, as he wrote in an 1859 journal entry lamenting the deforestation that had taken place in the wooded area where he had lived. It was his hope that “all Walden wood might have been preserved for our park forever, with Walden in its midst.”

In 1922 the Emerson, Forbes, and Heywood families donated approximately 80 acres of land surrounding the pond to the Commonwealth of Massachusetts, with the stipulation of “preserving the Walden of Emerson and Thoreau, its shores and nearby woodlands for the public who wish to enjoy the pond, the woods and nature, including bathing, boating, fishing and picnicking.” In the summer of 1935, some 485,000 people visited Walden Pond, with as many as 25,000 visitors on any given warm summer day. In 1965, the National Park Service designated Walden Pond as a Registered National Historic Landmark. In 1975, the Department of Environmental Management (DEM) was given the responsibility of managing the reservation, at which time the land became part of the Massachusetts State Forests and Parks system.

Human pressures

Shoreline after bank stabilization shows stone steps leading from the path to the water’s edge. Fencing was installed to protect newly established vegetation from being trampled. A requirement from the Department of Environemntal Management was to keep the park open and accessible as much as possible during construction. Wire fence was installed with minimal visual impact along both sides of the walking path.

People come to the reservation to hike, swim, fish, boat, and cross-country ski, with more than half a million visitors each year. The consequence of this heavy foot-traffic has, however, taken an apparent toll on the landscape. By the 1990s, it was recognized that severe erosion was occurring along the pond’s bank in areas where the hiking trail inadvertently captured and funneled rainfall runoff, causing deep gullies and other obstacles to form.

A team of Landscape Architects, bioengineers, and experienced contractors was hired by DEM to develop and implement an appropriate design strategy. The primary focus of the design was to stabilize the eroding bank with the use of bioengineering treatments, while establishing new viable path networks.

A bioengineering approach

Forested hillslope adjacent to the pond after bank stabilization shows vegetation that has become established on the steep slope with the aid of bioengineering techniques. In this section, coir blankets were installed along the slope, with a coir fascine placed along the trail’s edge for additional support and trail alignment.

As our landscapes have come to be recognized as functional watershed units, the many roles of vegetation have become increasingly valued. Bioengineered solutions to slope stability and water’s edge erosion problems go beyond physical protection – they establish vegetation, which in turn provides many important functions.

Bioengineering differs from conventional landscape plantings and bears little resemblance to row crop agriculture. Commonly, plants selected for bioengineering applications have fast-growing root systems and are physically strong as well as resistant to flood, drought, pests, and other impacts. Preferably, the plants are native to the area, and offer food, cover, resting and nesting areas, and other functions that add to their habitat value.

A bioengineering approach at Walden Pond

Shoreline after bank stabilization shows stone drainage swale and partially exposed coir blankets with well-established vegetation on the upper, less steep portion of the slope. Approximately 30,000 native plants were grown from seeds and cuttings collected from the reservation.

Beginning in the fall of 1996, The Bioengineering Group, Inc. worked with a team of collaborating Landscape Architects and engineers, including Walker-Kluesing Design Group and Emanouil Brothers, Inc., to prepare plans and specifications for the two-year construction project. Bank restoration of the 1,000 linear meters (3,281 linear feet) of shoreline involved the use of combined bioengineering techniques adapted for the unique conditions existing at Walden Pond. The goal was to imitate the existing natural vegetative patterns, using a variety of bioengineering treatments appropriately selected for the unique limnologic features and the high rate of erosive potential. The design, totaling approximately $100,000 for design fees with a total project cost of just over $ 1 million, was tailored to manage and enhance the site’s natural visual character.

To deter any future bank erosion, blueberry sod was staked into the moderately steep slopes above the path, with products such as coir blankets placed on the more gently sloping sections above and below the path. The slopes were then planted with live stakes (or dormant cuttings) and seeded with a mixture of native grasses. In areas where the banks were already eroding, brush layering was used, which involved the installation of live branches cut from trees such as willow and dogwood interspersed with layers of soil. The branches were situated in a crisscross or overlapping pattern so that the tips of the branches protruded just beyond the face of the fill.

Control of runoff from the upland areas to the pond was achieved by repairing gullies within the wooded slopes. The path was then graded to capture and suitably direct the runoff, carrying it by steep stone drainage swales to the pond. Aggressive mulching with native leaf litter was used to reduce surface runoff and to promote infiltration of the water into the soil.

In consideration of the site’s status as a literary pilgrimage, DEM requested that the plant lists compiled by Thoreau during his stay on Walden Pond be used for plant selection. In total, approximately 30,000 native plants were grown from seeds and cuttings collected from the reservation. Forty-five different species (approximately 70,000 individuals) of trees and shrubs were planted, while native plant species that may have otherwise been included for their hardiness and quick establishment could not be used if Thoreau had not listed them in his journals.

An additional requirement by DEM was to keep the park open and accessible as much as possible during construction. Planting design and maintenance strategies, therefore, had to take this factor into account. Pedestrian control was accomplished by installing a wire fence with minimal visual impact along both sides of the walking path.

The park today

Shoreline after bank stabilization shows combined use of vegetation and rock armoring. Forty five different species (approximately 70,000 individuals) of trees and shrubs were planted. DEM requested that the plant lists compiled by Thoreau during his stay on Walden Pond be used for plant selection.

Today, Walden Pond State Reservation remains a prominent focal point in eastern Massachusetts, with visitors coming from all parts of the world to experience a piece of the natural landscape that Thoreau found to be so vitally important. As a source of recreation and inspiration, Walden Pond State Reservation remains a representation of the park that every town should have, and will be for many years to come, with Walden in its midst.

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June 15, 2019, 10:24 pm PDT

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