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Alewife Stormwater WetlandCambridge, MA
Carbon Farming to Reverse Global WarmingDuke Bitsko, Director of Interdisciplinary Design
3 May 2015
Presentation Outline1. Project Overview
2. Native Habitat Planting Strategies
3. Vegetation Management Strategies
CSO Compliance
Project – Cambridge MA• Federal mandate to
clean Boston Harbor
• Reduces CSO’s by 84% or 43.6 million gallons annually to Mystic River
• Green Infrastructure includes downspout disconnect, porous paving, bioretention and constructed wetlands
Alewife Stormwater Wetland
• Largest stormwater wetland in Northeast (3.5 acres/10.3 acre-feet)
• Cleans, stores, reduces and releases stormwater to impaired stream system
• Integrates recreation, education and ecology
• Commitment to long-term management and monitoring
• State and City partnership
Project Components• Wetland Forebay; Water Quality Swale; Wetland
Basin; Oxbow/Floodplain; and Parkland
Plant CommunitiesVegetative Zones
• Permanent Pool 3’ – 5.5’ deep• Deep Marsh 18” - 3’ deep• Emergent Marsh: 6” - 1’ deep• High Marsh: 0 – 6” deep• Wet Meadow: Ephemeral, infrequent
inundation• Upland Riparian: slopes and islands
Wetland Basin - Plant Selection
• Pollutant removal capacity
• Natural habitat community-based
• Native to SE Massachusetts (no cultivars)
• Wildlife and cover value
• Commercially available
Wetland Basin Plantings
• Over 120,000 wetland plugs and tubers planted
• Habitats include open water, deep marsh, emergent marsh, high marsh, and wet meadow
Oxbow and Floodplain
Compensatory flood storage and increased habitat diversity Flap gate and flow connection to Wetland Basin Open water habitat harbors alewife species Spillway overflow and storage
DCR Parkland – Upland Habitat
• Scrub/shrub, Riparian Woodland (wet and dry) habitats
• All species native to SE Massachusetts; no cultivars used
City of Cambridge:• Outfall/inlet structures• Forebay/WQ swale• Wetland Basin• WQ testing (TP, N, coliform)
MA DCR:• Paths and boardwalks• Amphitheatre and signage• Non-wetland plantings
Operation and Maintenance Responsibilities
Vegetative Zones • Permanent Pool 3’ – 5.5’ deep• Deep Marsh: 18” - 3’ deep• Emergent Marsh: 6” - 1’ deep• High Marsh: 0 – 6” deep• Wet Meadow: Ephemeral, infrequent
inundation• Upland Riparian: slopes and islands
Stormwater Wetland – Deep Pool Sediment
Removal
Deep Pool Sediment Removal – 2 Step Process
1. Inspection: • Kayak and
measuring stick (hard clay bottom)
2. Sediment Removal:• Drought conditions
(July -September)• Vacuum truck hose
extension (from kayak) and/or manual removal
Water Quality Improvement• For the 1-month and 3-month storm
event - projected water quality enhancements:
1-month 3-monthContaminant Expected Removal
Rate Total Suspended Solids 65% 75%Lead 75% 80%Zinc 40% 40%Total Phosphorus 40% 40%Total Nitrogen 25% 30%
Source: Schueler 1992
Vegetation Management Plan
Components• Qualification of Wetland Scientist
• Statement of VMP Goals
• Description of Target Vegetation
• Vegetation Inventory
• Methods of Control/Seasonal Schedule
• Regulatory Compliance
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