The proponents of the Brown, et al., zoning petition assert that five areas in particular need to be addressed rapidly because they lack adequate protection
1) Increase the Flood Plain Overlay District (FPOD) to include the 500-year Federal Emergency Management Agency (FEMA) flood and the Cambridge Climate Change Vulnerability Assessment (CCVA) 2070 10-year Sea Level Rise/ Storm Surge (SLR/SS) flood.
Recent flood events throughout the US have indicated the FEMA 1% flood boundary, which is currently used as the FPOD boundary, is not a sufficient predictor of risk, and the 500-year (0.2%) boundary will be more appropriate as storms intensify. The CCVA identified sea level rise/storm surge as a new flooding concern for the future. We recommend using the areas subject to flooding in a CCVA 2070 10-year SLR/SS flood for inclusion in the Flood Plain Overlay District (FPOD). These flood delineations cover most of the predicted overland flooding without including flooding caused by the piped infrastructure, which shows up in the future precipitation and in larger SLR/SS events. These other areas that will be floodprone in the future can and should be addressed at a later time.
This new District definition is a significant reduction from the District boundaries originally proposed in Brown, et al. Reducing the area of the District to these new proposed boundaries essentially limits the FPOD requirements to the Alewife area and some small open space areas along the banks of the Charles River.
2) Require protection from flooding to an elevation, at minimum, equivalent to the future Base Flood Elevation (BFE), i.e. 1% flood, in 2070 and require compensatory storage for the 2070 1% precipitation storm.
FEMA recommends the lowest floor of new construction be above, at a minimum, the elevation of a 1% storm. For existing buildings that are being Substantially Improved or repaired for Substantial Damage as defined under the National Flood Insurance Program (NFIP), FEMA recommends the lowest floor must be raised to at least this standard, if not higher under state law or local ordinance. Since flood elevations are projected to rise over time, and future retrofitting will be expensive, we recommend using the future standard of 1% storms, rather than 10% storms per the draft Climate Change Preparedness and Resilience Alewife Handbook, during the time when the additional costs for lifting existing buildings are minimized as part of other construction efforts, to forestall flood damage and the need for subsequent retrofitting after damage.
Currently, state law requires that development in a floodplain must ensure that a project will not worsen the flooding of the surrounding area. One key part of the law is that if any floodwater storage that is available on the site for 1% storms will be displaced by the project, the displaced volume is required to be stored elsewhere on site or nearby (known as “compensatory storage”). Since Cambridge now has projections of flood levels for future storms, proposed new projects must prevent future displacement of the floodwater of corresponding future 1% storms. Compensatory storage in open space is preferred over fixed-volume, engineered structures to allow additional flood storage for storms larger than the one for which the storage is designed.
This requirement reduces the elevation from two-feet of freeboard above the 500-year storm, with additional freeboard for critical facilities, and removes the second-floor or higher requirement for residential units, from the original Brown, et al., petition.
3) Require 30% open space, with no exemption from the current 25% permeable open space requirement.
Open space can be used for floodwater and stormwater storage, and green infrastructure elements. We support the City’s current requirement of 25% permeable open space per Alewife Overlay District Section 20.96.1, but we would remove the exemption from it for using grey infrastructure stormwater storage in the FPOD.
The 30% open space requirement is unchanged from the original Brown, et al., petition. This new 25% permeable open space requirement is a reduction from the 30% percentage originally proposed in Brown, et al.
4) Require 10% tree canopy, public hearings for removal of trees larger than 6” caliper, and establish a method (setback; partial setback) that allows enough permeable area to support large, mature shade trees.
Site layouts need to allow space for the canopy of large, mature shade trees and for permeable ground around all trees to allow the root structures that support the canopy when mature. Mature trees along the south- and west-facing sides of buildings can greatly reduce the urban heat island effect.
This new 10% tree canopy to lot ratio is a significant reduction from the 30% percentage originally proposed in Brown, et al. A new 20-foot setback requirement at locations reserved for large trees is a significant reduction from the 25-foot setback on all sides originally proposed in Brown, et al.
5) Require reporting of Green Factor citywide; require a 0.35 Green Factor within the FPOD.
The requirement for reporting a Green Factor citywide for the larger Project Review Special Permit projects is a minimal imposition on such larger projects. It allows the City to easily collect data for a potential future threshold value for projects. While a value of 0.35 in the FPOD may appear small for a vulnerable natural resource area, because it is only marginally larger than the value other Green Factor cities require for their commercial districts, it is a reasonable minimum as a start for Green Factor implementation.
This requirement remains unchanged from the original Brown, et al., petition.
In addition to the new requirements that we feel are essential, there are a few items that are easy to implement. City policy requirements need to be explicitly codified through zoning or official policy statements. These include requirements for stormwater runoff, preparation of emergency plans, plans for site access and when access is not available, environmental reports. The City needs the jurisdictional authority to require project-specific accommodations that are municipal in origin, i.e. they cannot be overturned by the state for exceeding state requirements. For example, in their environmental reviews, the Conservation Commission and the permit. Granting allowances such as reduced parking minimums or increased building heights can help developers meet the new environmental safety requirements.