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STORMWATER MODELING & FLOOD MITIGATION STUDY UPDATE Melrose Neighborhood Association Meeting June 2020 ---PAGE BREAK--- Agenda • Study Background/Review • Use of Resident Survey Forms • Results of Study • Potential Projects ---PAGE BREAK--- Project Goals • Develop and calibrate a hydraulic model of Melrose watershed to simulate real world conditions • Evaluate and recommend alternatives to reduce the frequency and impact of area flooding • 3-inch, 1-hour storm - high intensity event ---PAGE BREAK--- Resident Survey • 163 Responses (1416 parcels in study area) • Used as an input for determining potential for basement backup • 10 year storm 24-hr): 40% at risk for backup • 3-inch, 1-hr storm: 50% at risk for backup • 500 year storm 24-hr): 70% at risk for backup • Used to calibrate hydraulic model and on street flooding depths ---PAGE BREAK--- 3-inch, 1-hour Storm Basement Backup Potential ---PAGE BREAK--- Conclusions • Collection system cannot handle high intensity short duration wet weather events without more storage • Many areas are inlet restricted intentionally, which allows water to pond on the street and not get into the system • Mitigating the 3-inch, 1-hr rain event requires removal or storage of 2,000,000 gallons water from the system JC1 ---PAGE BREAK--- Slide 6 JC1 Inlet restriction is intentional to allow water to pond onthe street and avoid putting additional water into the system causing basement backups. Joseph Coffey, 6/8/2020 ---PAGE BREAK--- Modeled flood depths of 3- in, 1-hour storm • Bottleneck effect at Western Ave and along Beaver Creek due to system capacity JC2 ---PAGE BREAK--- Slide 7 JC2 substitute sytem for limited. Joseph Coffey, 6/8/2020 ---PAGE BREAK--- Large Scale Alternatives • Alternative 1 - Collect and store combined sewage in a 2 million-gallon underground storage tank under Western Ave. Release flow by gravity back to the system when there is enough capacity. $15.1M • Alternative 2 - Partially separate combined sewer system and stormwater along Melrose, Homestead, and Western Avenues. Store the separated stormwater in underground 2 million-gallon storage tank and release flow by gravity back into the system when there is enough capacity. $17.4 M • Alternative 3 - Alternative 2 plus construction of force main and release into Buckingham Lake instead of the combined sewer. $17.4 M ---PAGE BREAK--- • Optimized potential storage locations allows us to perform phased projects with allocated funding. • Projects can be coordinated with DGS paving or other Water Department Capital Projects 463,000 gal JC3 ---PAGE BREAK--- Slide 9 JC3 this allows phased projects that can be performed on a scheduled basis with allocated funding. It also can be cordinated with DGSpaqving projects or other water department capital projects. Joseph Coffey, 6/8/2020 ---PAGE BREAK--- Small Scale & GI Alternatives 3 Concepts: Porous Pavement Underground Stone Reservoir Storage & Storm Sewer Separation Infiltration Porous Pavement with stone reservoir for storage and separated storm sewer/underdrain • Potential location – Winthrop Ave • 1000 feet long • 30’ wide • 18” deep storage • 18,000 cf (135,000 gal) storage • $280,000 - $350,000 • Tree Pits/Bioretention with small storage reservoir • Can be added to almost any project to increase storage • Typically 40-60 cf (300-450 gal) storage, but varies based on size of pit JC4 ---PAGE BREAK--- Slide 10 JC4 per Neil add a lot of photos from our other GI projects that illustrate options. Joseph Coffey, 6/8/2020 ---PAGE BREAK--- AWD Completed Small Scale GI Projects • Mereline Ave Sewer Separation & Stormwater Storage – Completed May 2020 • Provides approximately 320,000 gal of stormwater storage. • First street in Albany to have full width porous pavement. • Ramsey Place Green Infrastructure – Completed November 2019 • Provides approximately 150,000 gal of stormwater storage. • First street in Albany to use porous concrete slabs in parking lanes. • North Swan St Green Infrastructure – Completed December 2016 • Provides approximately 24,000 gal of stormwater storage • Bioretention and tree pits used for storage. ---PAGE BREAK--- Stone Reservoir and Storm Sewer Installation on Simpson Ave Mereline Ave Sewer Separation & Stormwater Storage MW3 ---PAGE BREAK--- Slide 12 MW3 Total Storage: 320,000 gal. Length of each cell ranges from 175 to 130 ft. Mallory Wright, 6/8/2020 ---PAGE BREAK--- Mereline Ave Sewer Separation & Stormwater Storage Regular Pavement Porous Pavement Regular Pavement Porous Pavement ---PAGE BREAK--- Underground stone storage reservoir and separated storm sewer Tree Pits Ramsey Place Green Infrastructure ---PAGE BREAK--- Ramsey Place Green Infrastructure Porous Concrete Panels Porous Concrete Panels ---PAGE BREAK--- Ramsey Place Before – 7/22/2019 ---PAGE BREAK--- Ramsey Place After – 4/9/2020 ---PAGE BREAK--- North Swan Green Infrastructure - Tree Pits with Bioretention