Integrating Habitat Restoration with Urban Stormwater Treatment at

Alewife Reservation, Cambridge, MA

Phil Rury, Duke Bitsko and Wendi Goldsmith

ALEWIFE RESERVATION ALEWIFE RESERVATION STORMWATER WETLAND PROJECTSTORMWATER WETLAND PROJECT

Project Team• Cambridge Dept. Public Works (client)

• MA Dept. of Conservation & Recreation (land owner)

• Engineering and Landscape Design Consultants– Kleinfelder/SEA (engineering & management)– MWH (site hydrology & hydraulic analysis)– Bioengineering Group (ecological design)

• Construction Contractor - P. Gioioso & Sons

Project History• Project is part of the MWRA Long-Term CSO

Control Plan for Alewife Brook Part of Court-ordered Boston Harbor Cleanup

• Designed to meet the goals and objectives of DCR’s Master Plan for Alewife Reservation Project of Cambridge DPW on DCR Land

Bioengineering facilitated collaboration of its clients DPW and DCR for mutual environmental benefit

CSO Control Plan for Alewife Brook

Goals Achieved to Date: Reduced Average Annual

Discharge to Alewife Brook by 48% since 1997

Cambridge closed CSO CAM 400 in March 2011

Stormwater Treatment Wetland is now under Construction

Goals of MWRA, Cambridge and Somerville: Reduce average annual CSO volume to Alewife Brook by 85% and

average frequency of discharge from 63 to 7 times a year Reduce flooding and sewer backup and Close CAM004 CSO

Alewife Stormwater Wetland

Project Location

Project Location15 acre Site between the Little River, Cambridge Park

Drive and Old Alewife Brook at Alewife MBTA StationIncludes 6.5 acres of existing, degraded freshwater wetland

Old Alewife Brook – Receives CSO CAM004 Discharge

Little RiverProject Location

Alewife T-Station

Alewife Reservation Plant DiversityA Richer Native Flora Inhabits Other Reservation Areas

and many more…

Onsite Wildlife Food Plants:

Alewife Reservation Wildlife16 Mammal Species including Beaver, Coyote, Mink, Muskrat, Rabbit, Raccoon, Red Fox, Weasel, White-tailed Deer, Skunk, Squirrel & Woodchuck

90 Bird Species including Grouse, American Woodcock, Raptors, Shorebirds, Song Birds, Turkey, Waterfowl and Waders

Mixture of Upland & Wetland Habitats Fragmented Wetlands – partly filled Altered Hydrology- starved of water Low Native Floristic Diversity Dominated by Invasive Vegetation

Degraded Site Conditions

• Invasive Plants Dominated 70% of Site: Ailanthus, Buckthorns, Honeysuckles, Japanese Knotweed, Multiflora Rose, Oriental Bittersweet & Phragmites

• Homeless Camps and Local Dumping

• Historically Filled Wetlands

Highly Degraded Site

Jungle of Invasive Vegetation

Purpose and ScopeStormwater Detention to Reduce Flows to Alewife Brook During Storms While Incorporating Goals and Objectives of

the DCR Alewife Reservation Master Plan

The stormwater treatment wetland system will improve water quality and:• Serve as a component of the larger CSO separation project• Detain over 10 acre-feet of water during storm events• Create or restore ecological functions/values of freshwater wetlands and

adjacent terrestrial habitats, emphasizing: Restoration of Severely Degraded Uplands and WetlandsFloristic Diversity and a Mosaic of Plant CommunitiesHydrologic, Water Quality and Wildlife Habitat Functions

Design Goals and Objectives

• Attenuate high volume stormwater flows • Enhance the quality of urban stormwater • Meet state and federal regulatory standards• Low maintenance/self-sustaining system• Create a sustainable and natural hydrology• Reduce invasives, promote native flora• Include components of Alewife Master Plan

Pollutant Removal Pathways within a Stormwater Wetland

• Prolong Detention and/or Retention to Settle Most Suspended Sediments

• Physical Filtration• Adsorption to Sediments• Groundwater Recharge• Microbial Breakdown • Plant Uptake

Soil Storage(peat)

Plant Uptake

Volatilizationof NH3 and

Volatile organics

Inflow

N2

DenitrificationNO3

-

Burial

Sedimentation

Plant Storage

CO2 & CH4

Adsorption- NH4

+, metals, P, organics (to clays, Fe / Al hydroxides, organic matter)Precipitation- P (with Fe, Al, Ca)- Metals (with sulfides)Source: K.R.

Reddy

Stormwater Detained to Elev. 1.0 ft.1-month Storm Event Hydrograph

0123456789

101112

Time (hours)

Flow

(cfs

)

Inflow Outflow

Water Quality ImprovementsWetlands can remove up to 90% of suspended solids,

heavy metals and nutrients from urban stormwaterExpected Removal Efficiencies for Rainfall Events

Contaminant 1-month 3-monthTotal Suspended Solids 65% 75%Lead 75% 80%Zinc 40% 40%

Total Phosphorus 40% 40%Total Nitrogen 25% 30%

COD [Bacterial Indicator] 35% 40%Source: Schueler 1992

• Improve Quality of Urban Stormwater • Flood Storage - No Net Increase of Discharge• Compensatory Aquatic and Wetland Habitats

Connected to Little River as Mitigation • Benefit from Clean Groundwater Inflows fed

by Head from the Fresh Pond Reservoir• Restore and Enhance Degraded Habitats• Aesthetics, Recreation & Education Benefits

Stormwater Wetland Design Criteria

Designed to Benefit from Groundwater Inflows fed

by GW Head from the Fresh Pond Reservoir• Oxbow Excavated into Sand and Gravel with

Ground Water Up to Elevation 3.0 feet• Valved Equalizing Pipe between Oxbow and

Main Basin to Feed Basin during Low Water• Parts of Main Basin are Perched on Clay –

Wetland Designed for Mean GW Elev. of 1.0 ft.

Stormwater Wetland Hydrology

Impounded Oxbow Water Level 1- 2 ft. > River Level

Surface Water Level of Impounded Oxbow Area Exceeds River Level

Top of Piers Set @ Elev. 2.0 ft.

Oxbow Water 1 foot Higher than adjacent Little River on 2/28/2012

Groundwater Influx @ 750 GPM

Diverse Wetland & Upland Habitats

Over 115,000 Wetland and 3,800 Upland Plantings Broadleaf Floodplain, Riparian & Upland Woodlands New Open Water Habitats of Main Basin and Oxbow Concentric Deep, Emergent and High Marsh Zones Scrub/Shrub Wetlands and Wet Meadow

Grading Plan - Forebay & East Basin

Main Outfall to Little River

Flow: Forebay to Vegetated SwaleForebay = 0.27 acres (50 ft. x 170 ft.)Inlet @ Elev. 0.0 ft.Outlet @ Elev. 1.0 ft.

Swale from Forebay Feeds First Pool

Planting Plan- Forebay & East Basin

Upland Peninsula to Divert Flow to West

Swale from Forebay Feeds First Pool

Compensatory Wetland CreationCreated Extra 0.71 acres of Oxbow Habitats connected to Little River to: Replace degraded finger of wetland used for channel creation and floodplain storage volume lost to create berm for the main basin wetland

Assure ground and surface water influx to basin up to surface water elevation of 1.0 foot

Add gravel bottom pond for Alewife spawning

Grading Plan - Oxbow & West Basin

Compensatory Oxbow Wetland Creation

Water Leveling Pipe

Planting Plan - Oxbow & West Basin

Deepest Pool 5.5 ft.

Gravel Bottom Pools 3.5 ft. Deep with River

at Elev. 1.0 ft.

Mosaic of Native Plant CommunitiesPlanting Zones along Moisture Gradient Ephemeral, Infrequent Inundation to Elev. 1.0 ft.Permanent Pools > 3’ deepDeep Marsh 1’- 3’ deepShallow Marsh 0 - 1’ deepScrub/Shrub & RiparianWet MeadowUpland/Peninsula/Island Meadow and Woodlands

Over 100 native species of live plantings and seed mixes were chosen for each plant community to

include many plant species already thriving on site

WETLAND HABITAT ACREAGES & SEED MIXES

Three Wetland

Seed Mixes Prescribed to Include Many Species to be Installed as

Live Plantings

High Marsh Mix: 23 Native Species

of 16 Genera

Construction Ecological OversightMADEP Wetland Permit & Water Quality Certification

require Oversight by a Resident Wetland ScientistAssure Compliance with All Permit ConditionsReview Contractor Submittals & Assure Conformance to Grading, Hydrologic, Soil & Planting Specifications Inspect and Accept Live Plantings and Seed Mixes Provide Bi-weekly Inspection Reports to MADEP

AGONY: FELLING LARGE NATIVE TREES!

ECSTASY: ERADICATING INVASIVE VEGETATION!

Soil Stripping for Disposal or Recovery

for Onsite Reuse:Strip > 6 inches Deep to Dispose of Invasive Roots and Seed BankRecover/Reuse Deeper Upland & Hydric Soils

Nice Surprise: Buried Hydric Soils!

Top 6-inches for Disposal

Deeper Topsoil for Reuse

Planting Soils Tested vs. Specs. @ 1 Sample per 1,000 CY

Subgrade Clay Sample for Soluble Salts

Dewatering via French Drains into:

Bag Filters, Floc Blocks, Filter Fabric and Straw Bales for Removal of Silt and Clay Colloids

Floristic Impact Mitigation• Preconstruction Rare Plant Reconnaissance

Botanist verified absence of state-listed Gentiana Andrewsii

Resident Ecologist Oversaw Invasive

Vegetation Removal and Stripping of Topsoil for Disposal

Identified Upland & Hydric Soils for Reuse

Oversees Dewatering & Erosion Controls

Fish & Wildlife Impact Minimization Construction timed to avoid migratory bird/fish breeding seasons Ecologist monitored for wildlife before/during clearing/grubbing Silt fences included numerous wildlife escape openings

American Woodcock and other sensitive birds nesting at the Reservation migrate south in October and

return in May

Wildlife Impact MitigationPreconstruction Site Reconnaissance for Resident Wildlife: Conferred with Wildlife

Relocation Experts Inspected site for

burrows, dens, nest sitesProvided “gaps” in silt &

construction fencingDaily site monitoring to

detect any fauna at risk

Wetland EstablishmentPost-construction Monitoring to:• Verify Establishment & Health of Vegetation• Replace Installed Plantings as needed • Assure Removal of Invasive Plant Species • Document Success for Certificate of Compliance• Guide Long-term Maintenance of Stormwater

Treatment Wetland by the City of Cambridge

Operation and Maintenance The City of Cambridge is committed to the

Continued, Long-term Maintenance of the Alewife Stormwater Wetland and

Compensatory Oxbow Wetland Habitats

Wetland design is fully integrated with the DCR’s Alewife Reservation and Greenway Master Plan to provide:

Water Quality Improvement Enhancements of Fish and Wildlife Habitat Improved Site Amenities Educational and Recreational Uses

Self-sustaining Wetland Ecosystem offers a Low Maintenance Solution!!

Alewife Reservation Project Benefits

Boardwalk with Overlooks onto Open Water and Wetlands will Support

Outdoor Education

Education and Recreation

Questions?