20.70 FLOOD PLAIN OVERLAY DISTRICT
20.71 Purpose. It is the purpose of this Section 20.70 to protect the health, safety, and general welfare, to protect human life and property from the hazards of periodic flooding, to preserve the natural flood control characteristics, and the flood storage capacity of the flood plain, to preserve and maintain the ground water recharge areas within the flood plain, and to provide a mechanism for a comprehensive review of development in the Flood Plain Overlay District and the design and location of flood water retention systems and their relationship to other surrounding development.
20.72 Establishment and Scope. There is hereby established a Flood Plain Overlay District which shall be governed by the regulations specified in this Section 20.70. The Flood Plain Overlay District includes all flood hazard areas designated as Zones A, AE, and X (Shaded) on the Middlesex County Flood Insurance Rate Maps (FIRMs) issued by the Federal Emergency Management Agency (FEMA) for the administration of the National Flood Insurance Program. The map panels of the Middlesex County FIRMs that are wholly or partially within the City of Cambridge are panel numbers 25017C0418E, 25017C0419E, 25017C0438E, 25017C0557E, 25017C0576E, 25017C0577E dated June 4, 2010. The exact boundaries of the District are defined by the special flood hazard area and moderate flood hazard area, which are the areas subject to flooding by the 1% and 0.2% annual chance flood, respectively, also known as the “100-year flood” or “base flood” (Special Flood Hazard area) and “500-year flood,” respectively, shown on the FIRMs and further defined by the Middlesex County Flood Insurance Study (FIS) report dated June 4, 2010. The FIRM and FIS reports are incorporated herein by reference and are on file with the City Clerk, Inspectional Services Department, Department of Public Works, Community Development Department and Conservation Commission.
The Flood Plain Overlay District shall also include within its boundaries the areas identified by either the 2015 Climate Change Vulnerability Assessment Part 1 Report or the 2017 Climate Change Vulnerability Assessment Part 2 Report as subject to flooding by the 1% annual chance flood for precipitation events, or the 0.2% annual chance flood for storm surge and sea level rise events, respectively.
20.73 Applicability. No structure or building shall be erected, constructed, expanded, substantially improved, or moved and no earth or other materials shall be dumped, filled, excavated, transferred or otherwise altered in the Flood Plain Overlay District unless a special permit is granted by the Planning Board. Where the provisions of this Section conflict with those found elsewhere in this Ordinance, the provisions of this Section shall apply.
20.73.1 A special permit shall not be required for any activity detailed in 20.73 above on individual lots containing one, two, or three family dwellings in existence as of July 5, 1982 or for the demolition of an existing structure. Nevertheless all other requirements of this Section 20.70 (and especially those criterion detailed in Subsection 20.75) shall be met as applicable.
20.74 Procedure. Application for a special permit shall be made on a form prescribed by the Board. In addition to the information required for the submittal, the applicant shall also present the following:
- A detailed landscape plan drawn to a scale of one inch equals twenty (20) feet showing the elevation and design of flood water retention systems as required by applicable law;
- Base flood elevation data, where the base flood elevation is not provided on the FIRM;
- Certification and supporting documentation by a Massachusetts registered professional engineer demonstrating that such encroachment of the floodway as specified above in Subsection 20.73 shall not result in any increase in flood levels during the occurrence of the 100-year flood;
- Such other technical information as necessary to permit the Planning Board to make the findings required in Section 20.75 below;
- Description of the status of the proposal, pursuant to the requirements of the Massachusetts Wetlands Protection Act, before the Cambridge Conservation Commission, including any Order of Conditions or Determination of Applicability issued; and
- Four (4) copies of all application materials.
20.74.1 Upon receipt of the application and development plans, the Planning Board shall transmit copies of the plans to the Conservation Commission and the City Engineer. Within forty-five (45) days of receipt of the plans, the Conservation Commission and the City Engineer shall review said plans and submit their respective reports and recommendations to the Planning Board. The Planning Board shall not render any decision on an application for a special permit for development in the Flood Plain Overlay District until said reports have been received and considered or until the forty-five (45) day period has expired without the receipt of such report, whichever is earlier.
20.74.2 Special Notification Requirements.
Where in the application it is proposed to alter or relocate a watercourse in a riverine situation, the Planning Board shall notify, in addition to those parties-in-interest required to be notified by Chapter 40A, all adjacent communities to the extent not required in Chapter 40A, the NFIP State Coordinator [Massachusetts Department of Conservation and Recreation, 251 Causeway Street, Suite, 600-700, Boston, Massachusetts 02114-2104 (or any successor office)] and the NFIP Program Specialist [Federal Emergency Management Agency, Region 1, 99 High Street, 6th floor, Boston, Massachusetts 02110 (or any successor office)].
20.75 Criteria. The Planning Board shall grant a Special Permit for development in the Flood Plain Overlay District if the Board finds that such development has met all of the following criteria in addition to other criteria specified in Section 10.43:
1. No filling or other encroachment shall be allowed in Zone A areas or in the floodway which would impair the ability of these Special Flood Hazard Areas to carry and discharge flood waters, except where such activity is fully offset by stream improvements such as, but not limited to, flood water retention systems as allowed by applicable law.
2. Displacement of water retention capacity at one location shall be replaced in equal volume at another location on the same lot, on an abutting lot in the same ownership, on a noncontiguous lot in the same ownership, or in accordance with the following requirements.
3. All flood water retention systems shall be suitably designed and located so as not to cause any nuisance, hazard, or detriment to the occupants of the site or abutters. The Planning Board may require screening, or landscaping of flood water retention systems to create a safe, healthful, and pleasing environment.
4. The proposed use shall comply in all respects with the provision of the underlying zoning district, provisions of the State Building Code, Wetlands Protection Act, and any other applicable laws.
5. Applicants for development in the Alewife area shall be familiar with area- specific and general city- wide land use plans and policy objectives (e.g. Concord- Alewife Plan, A Report of the Concord Alewife Planning Study, November 2005; Toward a Sustainable Future, Cambridge Growth Policy, 1993, Update, 2007; Section 19.30 - Urban Design Objectives of this Zoning Ordinance) and shall demonstrate how their plan meets the spirit and intent of such documents in conjunction with the requirements of this Section 20.70 - Flood Plain Overlay District and Section 20.90 – Alewife Overlay Districts 1-6.
6. The requirement of Section 20.74(3) has been met.
7. Applicants for development shall be familiar with and demonstrate compliance with the environmental aspects of area-specific and city-wide environmental and land use plans and policy objectives adopted by the City and shall demonstrate how their plan meets the spirit and intent of all such documents in conjunction with the requirements of this Section 20.70 - Flood Plain Overlay District.
Applicants for development subject to a Project Review Special Permit per Section 19.20 shall submit in their plans per Section 20.74.1 a complete list of relevant environmental objectives in the environmental and land use plans and policy objectives, and how their project complies with each relevant objective or why the objective cannot be met by the project. The Conservation Commission and the City Engineer shall submit in their respective reports reviewing the development plans, per Section 20.74.1, their assessment of compliance with the objectives and make appropriate recommendations to the Planning Board.
8. Applicants for development subject to a Project Review Special Permit per Section 19.20 shall submit in their plans per Section 20.74.1 the following documents:
1. Site Hydrology Report detailing hydrological impacts on surrounding properties
2. Soil and Groundwater Report on testing for potential contaminants
3. Stormwater Plan consistent with all MassDEP and City of Cambridge Stormwater Management Standards, Guidelines, and Best Management Practices (BMP) as defined in the Massachusetts Stormwater Handbook and other resources.
4. Emergency Plan as defined in Section 20.723
5. Tree Study per Section 8.66 of the City of Cambridge Code of Municipal Ordinances, which shall include a Tree Survey, a Tree Protection Plan, and, if applicable, a Mitigation Plan.
9. Applicants for development shall know and demonstrate compliance with the draft goals of the Envision Cambridge master planning process, including:
1. Improving access to open space and natural amenities;
2. Reducing and managing flood risk;
3. Mitigating storm water runoff pollution and improving the water quality of the Alewife Brook/Little Brook systems;
4. Mitigating the urban heat island effect, minimizing heat vulnerability, planning for outdoor thermal comfort, and factoring in the effect of rising temperatures on building energy;
5. Promoting social connections through well-designed public and publically accessible spaces; and
6. Encouraging creation of gathering spaces in conjunction with future private developments.
10. Applicants for development shall certify that the following building components shall be above the highest 500-year flood elevation identified by the documents in Section 20.72:
1. Lowest finished floor of interior space;
2. Critical mechanical and utility systems, in particular, those required to be operational as part of the Emergency Plan, as well as any intake or exhaust vents required for their continued operation;
3. Adequate building access/egress for emergency response during a flood event;
4. Storage of hazardous and/or volatile materials, including fuel in vehicles (per Section 20.720); and
5. All utility shut-offs and disconnects to the building.
20.705.1 Additional Special Permit Criteria for MMD-3: In granting a special permit for a Registered Marijuana Dispensary in the MMD-3 the Planning Board shall find that the criteria in 20.705 are met as well as the criteria in 20.705.1.
(a) Use Limitations: the RMD facility shall be retail only with no cultivation activities on the site.
(b) Siting: The RMD facility must be located either below grade or above the street level at the second story or above and be appropriately shielded from the public view.
(c) Size: The RMD facility size shall be less than ten thousand (10,000) square feet and at least seventy percent (70%) of the square footage shall be used for patient services and the remainder shall be devoted to administrative support, storage and security.
(d) Access to Public Transit: Areas with access to pedestrian and public transportation would be preferred.
20.76 Development Regulations for mobile homes. The following development regulations apply to the placement of mobile homes within Special Flood Hazard Areas designated as Zone AE on the FIRM, in addition to other requirements of this Section 20.70. All mobile homes shall provide that:
1. Stands or lots are elevated on compacted fill or on pilings so that the lowest floor of the mobile home will be at or above the base flood level; and
2. Adequate surface drainage and access for a hauler are provided.
20.76.1 The placement of mobile homes, except in an existing mobile home park or mobile home subdivision, is prohibited in the floodway.
20.77 Setback Exemptions. Any required flood water retention systems or related facilities may be permitted to extend into required yard setbacks if deemed appropriate by the Planning Board.
Setback Requirements. Notwithstanding dimension setback requirements for the underlying base zoning district, a minimum setback requirement of 25 feet shall be required to allow adequate space for mature shade trees identified in the Tree Study per Section 20.75.8.
20.78 Emergency Repairs. The special permit required in this Section 20.70 shall not apply to emergency repairs or projects necessary for the protection of the health, safety or welfare of the general public which are to be performed or which are ordered to be performed by a city agency, or the commonwealth, or a political subdivision thereof. In no case shall any filling, dredging, excavating, or otherwise extend beyond the time necessary to abate the emergency.
20.79 Any development activity requiring a special permit from the Planning Board under other provisions of this Zoning Ordinance shall incorporate the requirements of this Section 20.70 within the scope of that special permit and shall not require separate application to the Planning Board.
20.710 Open Space.
1. Minimum Open Space Area shall be no less than 30% of Gross Lot Area.
2. When a new development is proposed for a parcel greater than or equal to one (1) acre, the applicant shall be required to submit a Neighborhood Open Space Study to help frame and justify the location and amenities of on-site open spaces.
20.711 Permeable Open Space.
1. Minimum Permeable Open Space Area shall be no less than 30% of the Gross Lot Area.
2. Landscape designs shall provide as large a volume of structural soil as possible. A 36-inch depth from building face to back of curb is preferred, with a minimum standard of a 24-inch deep by 5-8 foot wide continuous trench parallel to the curb.
20.712 Tree Canopy.
1. Minimum Tree Canopy Coverage shall be no less than 30% of Gross Lot Area.
2. Existing trees larger than 6” caliper DBH that are to be removed shall require a tree hearing.
20.713 Building Access.
Proposals shall consider the installation of elevated sidewalks, pathways, and connecting structures to improve accessibility during flood events.
1. New construction and substantial improvement of any structure, including manufactured homes, shall have the lowest floor elevated two (2) feet above the 500-year flood elevation.
2. For Critical Facilities as defined in Section 20.721, new construction and substantial improvement of any structure, including manufactured homes, shall have the lowest floor elevated three (3) feet above the 500-year flood elevation.
3. For purposes of calculating building heights, all building height measurements shall be taken from grade, or from the 500-year flood elevation, whichever is higher.
4. Where the first floor of existing buildings is located below the 500-year flood elevation, such structures may be raised above the 500-year elevation by-right with the issuance of a building permit by the Inspectional Services Department, even when such raising results in a corresponding increase in height beyond maximum permitted dimensional requirements.
20.715 Flood Protection.
1. For new construction, all areas of the building located below the 2070 1% flood elevation shall be designed to recover from the 2070 1% flood event.
2. New construction shall adhere to the American Society of Civil Engineers (ASCE) 24-14 Flood Resistant Design and Construction (ASCE 24-14) standards below the 2070 100-yr flood elevation, including the use of building materials that maximize use of non-porous and/or inorganic materials and will be mold and mildew resistant.
3. All residential units shall be located on the second floor or higher.
4. Ceiling heights shall be 15’ or greater on the ground floor.
5. On-site backup energy generation and/or energy storage shall be provided for all life safety systems (e.g., potable water, elevators, lighting, ventilation, heating, cooling, etc.)
1.716 Storm Water.
1. All projects within the Flood Plain Overlay District, including street reconstruction, sewer, and drainage projects, shall maximize storm water absorption areas.
2. All projects shall conform to new storm water regulations and shall submit a storm water plan that demonstrates river water quality will not be degraded by runoff.
3. Because underground storage tanks have fixed volumes that cannot receive additional flood water in flood events larger than accommodated by the design and cannot adapt to increased flooding volumes caused by changes in climate, at least 50% of the volume of compensatory flood water storage under Section 20.75(2) shall be in open space areas unobstructed vertically to the level of either a current 0.2% probability per year flood event or a future 1% probability per year flood event, whichever is highest, as described in the most recently approved Climate Change Vulnerability Assessment or superseding document. Any fixed volume structure used for the remaining compensatory storage shall be 50% larger than the volume it is required to hold as required by Section 20.75(2) minus the compensatory volume allocated to open space regions.
4. Where onsite storm water detention is proposed, the enclosed area shall be designed by a registered architect or engineer to allow for the efficient entry and exit of floodwaters without human intervention. A minimum of 2 openings must be provided with a minimum net area of at least one square inch for every one square foot of the enclosed area. The lowest part of the opening can be no more than 12 inches above the adjacent grade.
5. Filling within the Special Flood Hazard Area shall result in no net loss of natural floodplain storage, or increase in water surface elevations during the base flood. The volume of the loss of floodwater storage due to filling in the Special Flood Hazard Area shall be offset by providing an equal volume of flood storage by excavation or other compensatory measures at or adjacent to the development site.
1.717 Cool Roofs.
1. To mitigate heat island effects, all roof surfaces, with the exception of Green Roofs as defined in Section 22.30, Overhangs or Sun-shading Devices as defined in Section 22.50, or Solar Energy Systems as defined in Section 22.60, shall be constructed as cool roofs.
2. Cool roofs shall have a minimum Solar Reflectance Index (SRI) of 82 (for rooftop slopes less than 10 degrees) and 39 (for rooftops over 10 degrees).
3. Non-roof surfaces shall have a minimum solar reflectance of 0.33.
Within the Flood Plain Overlay District, the following requirements shall apply to all new and substantially improved structures:
1. A development proposal may be exempted from minimum parking requirements upon review by the Planning Board, provided that such a reduction allows for additional permeable open space and/or residential units without restricting non-parking uses.
2. The maximum allowed parking ratio for residential construction shall be 0.5.
3. The maximum allowed parking ratio for commercial construction shall be equal to one (1) space per 1500 square feet of GFA.
4. Surface parking shall be limited to 10% of Gross Lot Area.
20.719 Flood Barriers.
Due to their potentially adverse impact on flood levels affecting neighboring properties, the approval of permanent flood barriers, berms, levees, walls, gates, or other flood control structures within the Flood Plain Overlay District shall be conditional upon the Planning Board’s issuance of a Special Permit. Such Special Permit shall be based on a finding of no adverse impacts to neighboring properties or the larger neighborhood.
20.720 Hazardous Materials and Waste.
1. Storage or processing of materials that are hazardous, flammable, explosive, or reactive to water within the Flood Plain Overlay District is prohibited. The storage of any of the following extremely hazardous and reactive materials is prohibited within the Flood Plain Overlay District without a Special Permit issued by the Planning Board:
• Calcium carbide
• Carbon disulfide
• Hydrochloric acid
• Prussic acid
• Nitric acid
• Oxides of nitrogen
• Other such materials as determined by the relevant City authority
2. In addition, the following items are sufficiently hazardous that the storage of larger quantities are prohibited in any space below the base flood elevation without a Special Permit issued by the Planning Board:
• Petroleum products, including gasoline or other motor vehicle fuels
• Acetylene gas containers
• Charcoal/coal dust
• Storage tanks
• Lumber or other buoyant items
3. Dumping or disposal of solid or hazardous waste is prohibited within the Flood Plain Overlay District. Storage of material or equipment not otherwise prohibited shall be firmly anchored to prevent flotation.
20.721 Critical Facilities.
Critical facilities are those developments which are critical to the community’s public health and safety; are essential to the orderly functioning of a community; store or produce highly volatile, toxic or water-reactive materials; or house occupants that may be insufficiently mobile to avoid loss of life or injury. The American Society of Civil Engineers Flood Resistant Design and Construction (ASCE 24-14) defines critical facilities as follows:
1. Per ASCE 24-14, Flood Design Class 3 structures are buildings and structures that pose a high risk to the public or significant disruption to the community should they be damaged, be unable to perform their intended functions after flooding, or fail due to flooding. Flood Design Class 3 includes (1) buildings and structures in which a large number of persons may assemble in one place, such as theaters, lecture halls, concert halls, and religious institutions with large areas used for worship; (2) museums; (3) community centers and other recreational facilities; (4) athletic facilities with seating for spectators; (5) elementary schools, secondary schools, and buildings with college or adult education classrooms; (6) jails, correctional facilities, and detention facilities; (7) healthcare facilities not having surgery or emergency treatment capabilities; (8) care facilities where residents have limited mobility or ability, including nursing homes but not including care facilities for five or fewer persons; (9) preschool and child care facilities not located in one- and two-family dwellings; (10) buildings and structures associated with power generating stations, water and sewage treatment plants, telecommunication facilities, and other utilities which, if their operations were interrupted by a flood, would cause significant disruption in day-to-day life or significant economic losses in a community; and (11) buildings and other structures not included in Flood Design Class 4 (including but not limited to facilities that manufacture, process, handle, store, use, or dispose of such substances as hazardous fuels, hazardous chemicals, hazardous waste, or explosives) containing toxic or explosive substances where the quantity of the material exceeds a threshold quantity established by the authority having jurisdiction and is sufficient to pose a threat to the public if released. Flood Design Class 3 structures shall be constructed with a first floor elevation of 3 feet above the 0.2% annual flood elevation.
2. Per ASCE 24-14, Flood Design Class 4 structures are buildings and structures that contain essential facilities and services necessary for emergency response and recovery, or that pose a substantial risk to the community at large in the event of failure, disruption of function, or damage by flooding. Flood Design Class 4 includes (1) hospitals and health care facilities having surgery or emergency treatment facilities; (2) fire, rescue, ambulance, and police stations and emergency vehicle garages; (3) designated emergency shelters; (4) designated emergency preparedness, communication, and operation centers and other facilities required for emergency response; (5) power generating stations and other public utility facilities required in emergencies; (6) critical aviation facilities such as control towers, air traffic control centers, and hangars for aircraft used in emergency response; (7) ancillary structures such as communication towers, electrical substations, fuel or water storage tanks, or other structures necessary to allow continued functioning of a Flood Design Class 4 facility during and after an emergency; and (8) buildings and other structures (including, but not limited to, facilities that manufacture, process, handle, store, use, or dispose of such substances as hazardous fuels, hazardous chemicals, or hazardous waste) containing sufficient quantities of highly toxic substances where the quantity of the material exceeds a threshold quantity established by the authority having jurisdiction and is sufficient to pose a threat to the public if released. Flood Design Class 4 structures shall be prohibited in all flood hazard areas, including the 1% and 0.2% flood areas.
20.722 Site Access.
1. New development shall not be permitted on dead-end roads. All project proposals shall include two (2) or more distinct vehicle access/escape routes.
2. Direct and contiguous dryland access shall be provided from each structure to land outside of the Flood Plain Overlay District. Where existing street elevations make compliance impossible , the Planning Board may permit new development or substantial improvements where access roads are at or below the base flood elevation, if:
a. the Planning Board has written assurance from police, fire, and emergency services that rescue and relief will be provided to the structure(s) by wheeled vehicles during a flood event; or
b. the Planning Board has determined that adequate shelter-in-place options, including backup power, heating/cooling, potable water, and food, are available to all building residents for the duration of a flood event.
20.723 Emergency Plans.
1. Such emergency plans as required in Section 20.75.8 shall address the following topics:
a. Flood warning protocols
b. Resident and/or employee notification procedures
c. Emergency preparedness plans and flood event procedures
d. Operation plans regarding the deployment of active flood protection measures (barriers, sand bags, etc.)
e. Access/evacuation plans during flood events
f. Onsite or local emergency shelter with food, potable water, shelter, heating/cooling, and backup power
g. Required disaster supplies
h. Procedures for the removal of all vehicles from flood-prone areas in order to protect the assets and livelihoods of residents and prevent flood water pollution from motor vehicle fuel, oil, and other contaminants.
2. Emergency Plans shall be publicly posted and accessible 24 hours per day onsite.
3. Emergency Plans shall assume event duration of no less than 72 hours.
20.724 Flood Markers. All structures shall prominently post flood markers on the exterior of each structure to show the depth of inundation during 100-year and 500-year flood events according to the City’s Climate Change Vulnerability Assessment or FEMA delineations, whichever is higher. The location of such markers shall be clearly described in the project application.
20.725 Removal of Lands from Flood Plain Overlay District.
Compliance with the provisions of Section 20.70 shall not constitute sufficient grounds for removing land from the Flood Plain Overlay District.
20.726 Variances Required.
Deviation from the requirements of Section 20.70 shall require a variance. Variances shall only be granted under the following conditions:
1. The variance shall be consistent with the goals and intent of Section 20.70;
2. The variance shall be the minimum relief necessary;
3. The variance shall not grant, extend or increase any use prohibited in the zoning district;
4. The variance shall not be granted for a hardship based solely on an economic gain or loss, or for a hardship which is self-created;
5. The variance shall not cause increased risks to public safety, present a nuisance to the public, or damage the rights or property values of other property owners;
6. The variance shall not cause any increase in the regional flood elevation; and
7. The variance shall not increase costs for public rescue and relief efforts.
20.727 Green Factor.
All projects within the Flood Plain Overlay District shall achieve a Green Factor score of at least 0.35, as defined by Section 22.80 – Green Factor of the Cambridge Zoning Ordinance.
20.728 Building Height.
Proposals for new construction may be exempted from existing base and overlay district height requirements upon the issuance of a Special Permit by the Planning Board, provided that the project, through such an exemption, does not exceed the allowed Floor Area Ratio for the underlying base and overlay districts, and also provided that such project has met all other requirements of Section 20.70 as to minimum Open Space, Permeable Open Space, Tree Canopy Coverage, Setback, Parking, and Green Factor requirements.