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CEHA Map Revision Process

The New York State Department of Environmental Conservation (DEC) is required to review the boundaries of New York State's Coastal Erosion Hazard Areas every 10 years, pursuant to Article 34 of the Environmental Conservation Law (ECL). In reviewing the boundaries of the Coastal Erosion Hazard Areas, ECL Article 34 and Title 6 of the New York Codes, Rules, and Regulations (6 NYCRR) Part 505 direct the Department to identify and map coastal areas subject to erosion, and landforms (such as beaches, bluffs, and dunes that protect coastal lands) and development from the adverse impacts of erosion and high water. Properties located within a Coastal Erosion Hazard Area are subject to regulation under ECL Article 34 and 6 NYCRR Part 505, which limit coastal development in order to protect these sensitive areas.

DEC is currently evaluating and revising the Coastal Erosion Hazard Area (CEHA) boundaries. Mapping technology has made huge advances since the creation of the current CEHA maps. Technologies such as high resolution oblique and orthoimagery, combined with LiDAR topographic data and field checks, have allowed for more accurate mapping than was previously possible. Orthoimagery and LiDAR data will be used to revise the maps using ESRI ArcGIS software, and the maps will be substantiated through the use of oblique imagery and field checks.

Types of Data Used in the CEHA Map Revision Process

LiDAR

LiDAR is an abbreviation for light detecting and ranging, and is a remote sensing process that is often used to determine topographic elevations. LiDAR is also used in many other applications, for example, meteorology and laser speed guns used by law enforcement. For the CEHA mapping, laser pulses were emitted at the ground from an aircraft mounted sensor, and the return time was measured to determine elevations (Figure 1).

The LiDAR that is being used for the CEHA map revision process has been acquired by several different sources, including the United States Army Corps of Engineers (USACE), the National Oceanic and Atmospheric Administration (NOAA) and the New York City Department of Information Technology & Telecommunications (DoITT). Additional information about LiDAR can found at the USGS Center for LiDAR Information Coordination and Knowledge (Click) website (http://lidar.cr.usgs.gov/).

Example of LiDAR DEM (Digital Elevation Model).
Figure 1. Example of LiDAR Derived Digital Elevation Model (DEM) flown by USACE. Differences in
elevations are visually represented by how dark or light an area is.

Orthoimagery

Orthoimagery is typically aerial imagery that has been gathered from a sensor mounted on an aircraft or a satellite. The imagery is then orthorectified; this process removes distortion and creates a spatially accurate image that can be used to make horizontal distance measurements (Figure 2).

The Orthoimagery that is being used for the CEHA map revision process has been acquired by USACE, DoITT, New York State Department of Environmental Conservation (NYSDEC) and Dewberry Engineers Inc.

Image of orthoimagery of Chimney Bluffs State Park in Huron, NY.
Figure 2. Example of orthoimagery depicting Chimney Bluffs State Park in Huron, NY.

Oblique Imagery

Oblique imagery is aerial imagery that is taken at an angle to the land; usually approximately 45 degrees (Figure 3). Oblique imagery allows for a less obstructed view of coastline features when compared to orthoimagery, which can sometimes be obscured by vegetation, shadows, and shoreline structures.

The oblique imagery that is being used for the CEHA map revision process has been acquired by USACE, NYSDEC, and Dewberry Engineers Inc.

Image of oblique imagery of Chimney Bluffs State Park in Huron, NY.
Figure 3. Example of oblique imagery depicting Chimney Bluffs State Park in Huron, NY.

The CEHA Map Revision Technical Process

The CEHA maps are comprised of two distinct zones, the Natural Protective Features Areas (NPFAs) and the Structural Hazard Areas (SHAs). The process for evaluating and revising these two areas are separate, but have some shared elements.

Natural Protective Features Areas (NPFAs)

The NPFAs, protect New York State's natural protective features (NPFs): nearshore areas, beaches, dunes, and bluffs. In order to ensure the accuracy of the proposed revised CEHA maps, the location and extent of these NPFs must be known. To do this, the LiDAR data is evaluated along transects (paths perpendicular to the shoreline on which measurements are made) placed every 50 meters. Elevation data is extracted along each of these transects, and that elevation data is used to determine the extent of the NPFs. After each NPF is properly identified, the most landward NPF is determined, and used to delineate the NPFA. Field checks are then conducted to verify the proper position of the NPFA in any areas of concern.

Structural Hazard Areas (SHAs)

The SHAs are regulated areas landward of the NPFAs. SHAs are only delineated in highly erosive shoreline areas with a yearly erosion rate greater than 1 foot/year. The purpose of defining SHAs is to limit permanent (non-movable) construction in areas where damage due to erosion has a high probability of occurring during the life of the structure.

The locations of the SHAs are determined by comparing the shoreline location between historic imagery from the 1970's and 1980's and present day data. The difference in shoreline location between the two time periods determines the shoreline recession rate. If this historic shoreline recession rate is calculated to be greater than 1 foot per year at a given transect, the erosion rate is then rounded to the nearest ½ foot and delineated as a SHA. Areas with recession rates less than 1 foot per year are not rounded up to 1. The landward extent of the SHA is determined by beginning at the NPFA line, and extending landward a distance equal to the rounded annual erosion rate x 40 feet. Examples of SHA calculations are represented in the table below.

Examples of Structural Hazard Area (SHA) Calculations
Calculated Erosion Rate
(feet/year)
Rounded Erosion Rate
(feet/year)
Approximate Setback
from the NPFA Line (feet)
0.9 NA 0
1.2 1.0 40
1.6 1.5 60
1.9 2.0 80
2.3 2.5 100

Anatomy of Proposed Revised CEHA Map

Figure 4 and 5 are two examples of the proposed revised CEHA maps. The map components are briefly described below; the numbers in the image correspond to the numbers listed in the description of the map components.

Example of preliminary CEHA map with several map components labeled.
Figure 4. Example of a proposed revised CEHA map with several map components labeled. The map components are described in the list below.

Description of Map Components

  1. Title Block. The Title block includes:
    • Map Location- City/Town/Village/Borough, and County
    • Certification Date
    • Photo Number (name of orthoimagery photograph used on map)
    • Sheet Number
  2. Scale - in both feet and meters. Only maps printed on 11x17 paper are scalable.
  3. North Arrow
  4. Legend
  5. Revisions Table - contains records of any map revisions after certification date.
  6. Landward Limit of Structural Hazard Area
  7. Landward Limit of Natural Protective Feature Area
  8. Historic Shoreline Recession Rates
  9. Most Landward NPF Label Line
  10. Jurisdictional Boundaries - City/Town/Village/Borough/Reservation
  11. Match Lines - match lines assist in orientation of map panels. If match lines from adjacent map panels are superimposed, the panels will display the correct orientation with respect to one another.
Blown up section of the preliminary CEHA map example with several map components labeled.
Figure 5. Blown up section of a proposed revised CEHA map with several map components labeled.

More Information

For more information, please visit the Coastal Erosion Management Program webpage.