WATERWORKS : SUPPORTING SUCCESSION

How can construction for stream stability and ecosystem regeneration allow for stream succession and change over time? This design enables dynamic processes, giving space for the stream to succeed over time and elevating the human experience above the ecosystem with an all-persons boardwalk and observation deck.

hydro-ecologIcal changes

• The southern third of the lawn is seeded with tall meadow grass and forb species.

• Invasive species are removed and the area is planted with competitive native floodplain species such as alder, willow, and silky dogwood.

• The concrete channel and dam are removed and repurposed as lunkers, a structure that helps stabilize banks and increases fish habitat.

• Dredged sediment is reused to develop emergent marsh ecosystems along the banks to benefit water quality, and aquatic and wetland habitat.

• Bioengineering features such as step pools, live stakes, fabric-encapsulated soil lifts, lunkers, and root wads slow water, stabilize the bank, and establish the toe of the marsh. See sheet 32 for bioengineering details.

The Human Element

• A new bridge longer than bankfull width allows for more natural change in the stream channel.

• Existing trails to the south of the stream are rerouted to limit the degradation of the slope.

• An out-and-back all-persons boardwalk and trail leads to an overlook.

• An overlook observation deck allows park-goers to connect with the restored stream.

• A new trail connects the observation deck to the existing trails leading to the Laurel Pond area.

Pros

• Embraces the highly dynamic stream system, allowing ample space for stream succession and change.

• Increased aquatic and wetland habitat.

• Terraced marshes and riparian areas slow, capture, and infiltrate stormwater and increase floodplain access.

• All-persons boardwalk and observation deck allow people to connect with the stream while limiting human disturbance.

• Creating access for construction is an opportunity to remove invasive species and replant with competitive native species.

Cons

• Will require significant disturbance during construction.

• Disturbance will encourage recolonization of invasive species and will require active management for at least five years.

InstallatIon / maIntenance

• Installation will require vast clearing, though this provides ample opportunities to remove invasive species and restore native riparian/ floodplain vegetation to increase floodplain access.

• Native plant revegetation will require intensive maintenance for the first five years, but reduce maintenance in the long-term.

• Helical piles may anchor the boardwalk, causing less disturbance to the wetland marsh than other methods.

• The bioengineering strategies like fabric-encapsulated soil lifts, step pools, live stakes, root wads, and lunkers, will require skilled technicians for installation.

• Mowing is reduced by a third. The mow-path follows the southern edge of the all-persons trail.

Conceptual Design Details 1

The stream cross-section shows the relationship between the human experience and the dynamic stream ecosystem. The stream profile shows the change in stream gradient, with step pools reducing flow velocity upon dam removal.

WATERWORKS : PRESERVE THE PUMP

How much infrastructure is necessary to remove for stream health? When does the level of disturbance outweigh the benefits of a “natural” channel? In answering these questions, this design also strives to maximize human / stream connection in this location.

hydro-ecologIcal changes

• A native meadow is established in the turf area to increase habitat and decrease runoff, with a mown path providing a shortcut to the all-persons trail.

• The dam and buried clay pipe are removed, replaced with boulder step pools to make up for the elevation change.

• A notch is cut in the concrete reservoir wall to create a new stream channel and flow into the concrete channel is blocked off.

• Fabric-encapsulated soil lifts (FESL) stabilize the worst bank failure and a new trail with infiltration steps provide access to a cobblestone beach.

• Wetland areas are allowed to form naturally before and after the concrete reservoir, where the water slows.

The Human Element

• An all-persons trail loop is constructed, using a mix of boardwalks and stone dust to bring people right into the stream and encourage interaction.

• Shrub species are planted around the trail’s switchback to discourage cutthroughs and also to soften the transition from forest to meadow ecotype.

• The areas heavily disturbed by the infrastructure removal are replanted with native riparian vegetation, blocking views of the stream and creating a sense of mystery and discovery along the trail.

• An interactive pump activity allows visitors to reactivate the concrete channel when they use the pump, celebrating the waterworks history and recalling when this area was the town’s swimming hole called “The Pump.”

• A viewing platform creates a destination and a vista overlooking the reservoir area.

Pros

• Less disturbance to site than the first Waterworks design.

• Creates destinations and learning opportunities.

• Celebrates history of human interaction with the site.

• Increases wetland areas and reestablishes some floodplain access.

Cons

• Concrete reservoir limits the connection between the aquatic, wetland, and riparian ecotypes.

• Would require lots of new trail construction.

• Amount of boardwalk increases cost.

InstallatIon / maIntenance

• Installation will require vast clearing, though this provides ample opportunities to replant with native vegetation to increase ecosystem function.

• Concrete channel and hand pump will likely require design, engineering, and maintenance.

• Meadow and shrubland will require little (yearly) maintenance once established.

• Step pools may require periodic maintenance.

LAUREL POND : SUMMARY ANALYSIS

Steep slopes and flooding impacts park amenities and causes erosion on turf slopes. The dam traps vast quantities of sediment annually, reducing water quality and aquatic habitat.

Cooley Brook enters an emergent marsh through a three-foot-wide culvert under Laurel Street, meandering through wetlands before entering open water. Vast amounts of sediment erode from the steep banks in Bliss Park and is carried by the stream until trapped by the dam on the pond’s western edge. Steep slopes (>33%) surround the pond, where seasonal change in water flow has begun to erode the turf-dominated banks. 100-year flood events inundate many of the human-centered features of the area including trails, bridges, and lawn. The processes of erosion and deposition are out of balance in this area, creating challenges for pond maintenance, increasing risk of failure for existing road and stream infrastructure, and reducing both water quality and viable aquatic habitat. Removal of the dam and altering the stream channel using bioengineering strategies may help improve flood storage, improve water quality, and increase aquatic habitat and connectivity.

Key Terms

Sediment forebay: a basin or storage structure designed to dissipate the energy of incoming runoff and allow for initial settling of course sediments

All-persons trail: trail designed and built to be accessible to everyone

Riparian: relating to wetlands or adjacent to rivers and streams

ADA (Americans with Disabilities Act): a civil rights law that prohibits discrimination against individuals with disabilities in all areas of public life

Reinforced turf: turf stabilized with structural paneling to increase stability and load-bearing capacity

Escarpment: a vertical face of exposed bedrock

Bioengineering: increasing the strength and structure of the stream channel with a combination of biological and mechanical elements

Assets

• An emergent wetland is forming naturally on the east end of Laurel Pond

• A sloped south-facing lawn creates positive views of the pond and surrounding landscape

constraInts

• 100-year flood covers bridges, trails, and other human-centered spaces

• The dam’s structural integrity is unknown, as it has never been assessed

• Extreme amounts of sediment behind the dam are causing poor water quality

• The unclear boundaries of the parking area creates a free-for-all for rogue parking

• The undersized culvert shows signs of erosion and scour holes around its outfall in the emergent marsh