1. Integrating Habitat Restoration with
Urban Stormwater Treatment at
Alewife Reservation, Cambridge, MA
Phil Rury, Duke Bitsko and Wendi Goldsmith

2. ALEWIFE RESERVATIONALEWIFE RESERVATION
STORMWATER WETLAND PROJECTSTORMWATER WETLAND PROJECT

3. 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

4. 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

5. 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

6. Alewife Stormwater Wetland
Project Location

8. Project Location
15 acre Site between the Little River, Cambridge Park
Drive and Old Alewife Brook at Alewife MBTA Station
Includes 6.5 acres of existing, degraded freshwater wetland
Old Alewife Brook – Receives
CSO CAM004 Discharge
Little River
Project Location
Alewife T-Station

9. Alewife Reservation Plant Diversity
A Richer Native Flora Inhabits Other Reservation Areas
and many more…
Onsite Wildlife Food Plants:

10. Alewife Reservation Wildlife
16 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

11.  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

12. • 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

13. Jungle of Invasive Vegetation

14. Purpose and Scope
Stormwater 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 Wetlands
Floristic Diversity and a Mosaic of Plant Communities
Hydrologic, Water Quality and Wildlife Habitat Functions

15. 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

16. 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
Volatilization
of NH3 and
Volatile organics
Inflow
N2
Denitrification
NO3
-
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

17. Stormwater Detained to Elev. 1.0 ft.
1-month Storm Event Hydrograph
0
1
2
3
4
5
6
7
8
9
10
11
12
0:00
2:00
4:00
6:00
8:00
10:00
12:00
14:00
16:00
18:00
20:00
22:00
Time (hours)
Flow(cfs)
Inflow
Outflow

18. Water Quality Improvements
Wetlands can remove up to 90% of suspended solids,
heavy metals and nutrients from urban stormwater
Expected Removal Efficiencies for Rainfall Events
Contaminant 1-month 3-month
Total 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

19. • 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

20. 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

21. 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

22. 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

23. Grading Plan - Forebay & East Basin
Main Outfall to Little River

24. Flow: Forebay to Vegetated Swale
Forebay = 0.27 acres
(50 ft. x 170
ft.)
Inlet @ Elev. 0.0 ft.
Outlet @ Elev. 1.0 ft.
Swale from Forebay
Feeds First Pool

25. Planting Plan- Forebay & East Basin
Upland Peninsula to
Divert Flow to West
Swale from Forebay
Feeds First Pool

26. Compensatory Wetland Creation
Created 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

27. Grading Plan - Oxbow & West Basin
Compensatory Oxbow Wetland Creation
Water Leveling Pipe

28. Planting Plan - Oxbow & West Basin
Deepest Pool 5.5 ft.
Gravel Bottom Pools
3.5 ft. Deep with River
at Elev. 1.0 ft.

29. Mosaic of Native Plant Communities
Planting Zones along
Moisture Gradient
Ephemeral, Infrequent
Inundation to Elev. 1.0 ft.
Permanent Pools > 3’ deep
Deep Marsh 1’- 3’ deep
Shallow Marsh 0 - 1’ deep
Scrub/Shrub & Riparian
Wet Meadow
Upland/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

30. WETLAND HABITAT ACREAGES & SEED MIXES

31. Three Wetland
Seed Mixes
Prescribed to
Include Many
Species to be
Installed as
Live Plantings
High Marsh Mix:
23 Native Species
of 16 Genera

32. Construction Ecological Oversight
MADEP Wetland Permit & Water Quality Certification
require Oversight by a Resident Wetland Scientist
Assure Compliance with All Permit Conditions
Review 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

33. AGONY: FELLING LARGE NATIVE TREES!

34. ECSTASY: ERADICATING INVASIVE VEGETATION!

35. Soil Stripping for
Disposal or Recovery
for Onsite Reuse:
Strip > 6 inches Deep
to Dispose of Invasive
Roots and Seed Bank
Recover/Reuse Deeper
Upland & Hydric Soils
Nice Surprise: Buried Hydric Soils!

36. 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

37. Dewatering via French Drains into:
Bag Filters, Floc Blocks, Filter Fabric and Straw Bales
for Removal of Silt and Clay Colloids

38. 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

39. 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

40. Wildlife Impact Mitigation
Preconstruction Site
Reconnaissance for
Resident Wildlife:
Conferred with Wildlife
Relocation Experts
Inspected site for
burrows, dens, nest sites
Provided “gaps” in silt &
construction fencing
Daily site monitoring to
detect any fauna at risk

41. Wetland Establishment
Post-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

42. 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

43. 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

44. Boardwalk with Overlooks
onto Open Water and
Wetlands will Support
Outdoor Education
Education and Recreation

45. Questions?