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Natural Features Protected by the SNAD

Disclaimer This overview of SNAD regulations is provided for informational purposes only—the actual regulations are much more complex than this overview.

Contact the Bronx Office of City Planning, at 718-220-8500, with your specific project plans and a description of your property, to ensure that you comply with all zoning requirements. City Planning will guide you through the approval and permitting process.

Natural features that are protected under SNAD include, but are not limited to (Sect. 105-11 of the zoning regulations):


Healthy trees of 6" caliper or greater are protected under SNAD. What is Caliper?

  • Caliper is the diameter of the tree trunk measured 4 feet 6 inches from the ground.

  • If the trunk splits below this height, the trunk is measured at its most narrow point below the split.

Healthy trees of 6" caliper or more may be removed only if (Sect. 105-31, a-d):

  • The tree is located in areas to be occupied by your development project, or it is within a distance of 15 feet from the exterior walls of a building,

  • The continued presence of the tree would create special hazards or dangers to persons or property,

  • The tree will interfere with the growth or health of another tree that is designated for preservation, or

  • An authorization has been granted by the City Planning Commission approving its removal.

Trees that are removed may need to be replaced.

The Department of City Planning will advise you of the number of trees you must plant to replace those you remove. What about unhealthy trees? A tree of 6" caliper or greater that is dead, diseased, or imminently hazardous to property or persons may be removed without special review. When removing such a tree, you must obtain a letter from a certified arborist documenting the tree's condition and justifying its removal.

Topography (including steep slopes)

Modifications to a slope can affect stormwater and groundwater drainage patterns, soil conditions, and vegetation health. In the SNAD, lots are characterized as:

  • Tier I - average slopes of < 10 %

  • Tier II - average slopes of 10 % or greater (includes "steep slopes")

  • steep slopes - slopes of 25 % or greater

Maximum Lot Coverage What is Lot Coverage? Lot Coverage is the portion of a zoning lot which, when viewed from above, is covered by a building or portion of a building.


Slope Zoning District Permitted Maximum Lot Coverage


steep slope R1,R2,R3 12.5%

steep slope R4 20.0 %

10 - 14.9 % R1 - R4 varies from 22.5 to 36 %

15 - 19.9 % R1 - R4 varies from 20.0 to 32 %

15 - 19.9 % R1 - R4 varies from 20.0 to 32 %%


Grading Restrictions


Topography Category Grading Regulation Zoning Regulation


Projects that do not require a Review by Department of City Planning Section 105-021, b

building permit, such as Required for changes to topography of some swimming pools, garden more than two feet

sheds, or fences

Tier I Sites: Projects that require a building Authorization from the City Planning Section 105-421

permit Commission required for any modification

of existing topography.

Tier II sites: Projects that require a building Authorization from the CPC Section 105-34

permit for any grading beyond 15 feet of the location

of a building foundation (with the exception

of driveways and private roads) Grading within

15 feet of a foundation is subject to regulations

for cut and fill slopes, compaction of fill,

retaining walls, and other grading elements.

Driveways and private roads Section 105-35



Topsoil is protected from erosion during construction. "Any exposed earth shall have straw, jute matting , or geotextiles placed on it within two days of exposure and be seeded with annual rye grass during construction." (Section 105-36, (f)) A development on a Tier II site, that needs an authorization, must install one of the following erosion and sedimentation control measures: benches and berms, diversion channels, debris or sediment basins, retention ponds, or grassed waterways or outlets. (Sect. 105 -37)

Rock Outcrops and Erratic Boulders

The geology of Riverdale is displayed in its outcrops and boulders. These are of interest to scholars and residents, and are protected from modification as follows: A rock outcrop is a piece of bedrock exposed at the surface. Modification or alteration of a rock outcrop must always be authorized by the City Planning Commission. (Section 105-424)

An erratic boulder is a boulder that originated elsewhere and was carried and deposited at its current location by water or ice (in the Riverdale area generally by glacier ice). Erratic boulders of less than 6 feet in diameter may be moved. Erratic boulders "with a diameter at any point of 6 feet or more" may only be moved by authorization of the City Planning Commission. (Section 105-423)

Wetlands and Surface Water Features

Modification of a wetland or surface water feature must always be authorized by the City Planning Commission. (Sect. 105-426)

Botanic Environments

Botanic environments, where they exist, are part of the defining characteristics of the SNAD and are to be protected or replanted under SNAD regulations. What are botanic environments? Botanic environments are assemblages of plants adapted to specific environmental conditions. They are characterized as primary succession communities, secondary succession communities, climax communities, dune or heathland, and wild grasslands. They consist of varying proportions of ground cover, shrubs, small trees, and large trees. The goals of replanting are to reproduce:

  • the plant assemblages that are removed, or another assemblage determined characteristic of the area

  • an entire ecosystem, including but not limited to ground covers, annuals, perennials, herbs, vines, and woody plants, and with consideration of the fauna that is dependent on the plants

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