Conceptual Urban Block in Cambridge – Designing for Maximum Climate Resiliency

Overview

The City of Cambridge conducted a Climate Change Vulnerability Assessment  (CCVA) in 2015 and 2017 to identify areas that are more susceptible to climate risks of flooding and extreme heat. From the CCVA reports, the City identified Alewife and The Port as two pilot neighborhoods to inform the development of a citywide Climate Change Preparedness and Resiliency Plan (CCPR). Kleinfelder is the lead consultant and technical lead for both the CCVA reports, the pilot neighborhood plans and the citywide plan. It is supported by urban drainage modeling lead Stantec, energy consultant Buro Happold, and Weston and Sampson.  Kleinfelder has also contributed to the Urban Forest Master Plan, led by Reed Hilderbrand, and several technical analyses for coastal flood modeling by the Woods Hole Group informing climate change planning in Cambridge.

The CCPR Plan for The Port was released in May 2019. The Port neighborhood is representative of many Cambridge neighborhoods. It is a high-density residential area with a high percentage of renters (~70% of residents are renters), a dense underground infrastructure, including combined sewer and stormwater pipes, and a mix of small businesses, science buildings, and institutional uses. Flooding from precipitation and heat vulnerability are imminent concerns for the City as this neighborhood is already experiencing flooding during extreme rain-event and has less greenery being more subject to extreme urban heat. Climate change is expected to further exacerbate future risk from flooding and extreme heat in The Port.

What is the main idea?

The Kleinfelder team developed a super-resilient urban block concept as part of The Port CCPR. The urban block concept presents an opportunity for innovative projects in the neighborhood to demonstrate how maximum resiliency efforts for buildings, drainage and energy systems, and ecosystems can reduce flooding and the urban heat island (UHI) effect and increase energy resiliency in one defined area. This approach maximizes resiliency and sustainability strategies to test how efforts in strategic locations could benefit the resiliency of the overall neighborhood.

Click Here to View Figure 1. Conceptual design of a resilient urban block

The mixed-use urban block shown in Figure 1 is located between Portland and Moore Streets immediately south of Broadway in Cambridge, MA. By implementing a combination of gray and green infrastructure projects in the block, it demonstrates the potential performance of maximum resiliency for buildings, drainage and energy systems, and ecosystems can reduce flooding and the urban heat island effect and increase energy resiliency in one defined area. Our modeling demonstrated that significant benefits could be achieved in the best-case scenario (Figure 2).

Click Here to View Figure 2. Maximum projected benefits for the implementation 
of strategies for the mixed-use block​

What is the best-case scenario?

For buildings: Of the 35 buildings in the mixed-use block, gray and green infrastructure improvements can be implemented throughout to make meaningful progress toward resiliency:

•  Roofs make up 48% of the total area in the mixed-use block. Assuming 25,000 square feet of roofs in the mixed-use block were to be completely renovated or newly constructed as white/blue roofs holding up to 4.5 inches of rain, it would be possible to detain up to 9,400 cubic feet (70,100 gallons) of stormwater during the peak of an extreme rainstorm. White/blue roofs can also reduce the urban heat island effect. Including additional green roofs would further reduce both stormwater runoff and urban heat island effect.

• Solar photovoltaic (PV) systems added to building roofs improve the ability to stay safe (“passive survivability”) if the building is cutoff from the electricity grid and connected to an energy storage system. Solar PV can be installed on any roof with moderate to good solar access and structural strength.
• Build/protect to the 2070 10-year flood elevation from precipitation or sea level rise/storm surge, whichever is higher, and recover to the 2070 100-year flood elevation from precipitation or sea level rise/storm surge, whichever is higher.
• Design buildings using the American Society of Civil Engineers (ASCE) 24- 14 Flood Resistant Design and Construction as a reference when site is below the 2070 100-year flood elevation.
• Design buildings with passive strategies including building orientation, high-performance building envelope (e.g., R-20 minimum wall insulation and R-40 minimum roof insulation, U-0.3 maximum glazing), shading, natural ventilation, and white or green roofs, and limit air leakage (less than or equal to 3 air changes per hour (ACH) at 50 pascals).

For site resiliency: Whether a building retrofit or a new construction, site improvements provide opportunities for increased resiliency to adapt to increased precipitation and/or extreme heat. The mixed-use block has 52% nonbuilding space, this space presents opportunities for additional gray and green infrastructure implementation.

• Replace existing conventional pavement with porous pavement or pavers; 28,000 square feet replaced could improve localized flooding impacts. Porous pavement or pavers with a solar reflectivity index (SRI) of at least 29 will reduce urban heat island effect.
• Approximately 3,000 square feet of existing landscaped area within Greene Rose Heritage Park and adjacent residential properties are suitable for conversion into a rain garden.
• Greene Rose Heritage Park in the mixed-used block presents an opportunity for stormwater storage. The park currently has an underground 500-gallon infiltration tank, which could be upgraded to either a storage tank or storage feature within the park.
• The City can replace six existing catch basins with leaching catch basins (conceptual design shown in Figure 3) to capture street stormwater runoff. To maximize storage, make lateral connections to tree box filters.

Click Here to View Figure 3. Example of a cross connected 
tree-box filter and leaching catch basin

Implementation

As part of the ongoing streetscape and utility work in The Port neighborhood - and in conjuncture with the stormwater and sewage tank projects at Parking Lot 6 and Morgan Park -  Kleinfelder is working with the City to evaluate public right-of-way and adjacent private parcel opportunities for implementation of an extensive toolkit of green infrastructure solutions. Prior modeling analyses by Stantec, performed in coordination with Kleinfelder and Cambridge DPW as part of the CCPR Port Preparedness Plan and Port Short-Duration Storm (or "flash" flooding) follow-on modeling, have helped the City quantify the potential flood mitigation benefits of green stormwater infrastructure BMPs, which include bioretention/rain gardens, curb bump outs, tree trenches, porous driveways, downspout planters, and subsurface detention/infiltration facilities. In the summer of 2020, a neighborhood-wide field investigation was performed to assess the suitability and feasibility of these BMPs, which consisted of field surveying, cataloging of existing roof and driveway drainage conditions, available space, and utility conflicts.  The City plans to best leverage opportunities for green infrastructure in order to maximize co-beneficial outcomes during implementation, including mitigation of UHI impacts, maximizing tree planting (in line with Urban Forest Master Plan goals), and improving Charles River water quality. 

In the months ahead, the project team will be working with Cambridge DPW and the City’s Port Infrastructure Working Group to conduct outreach with private property owners and residents, helping identify green infrastructure retrofit opportunities on adjacent private parcels where implementation may coincide with upcoming work in the public right-of-way.