Using LiDAR For Map Amendments
LiDAR data can replace the requirement to submit elevation information
certified by a licensed land surveyor or professional engineer, which can create
a cost savings for property owners. However, LiDAR data may be less accurate
than certified elevations and may not capture the full risk for the building or
lot.
For more information on the standard LOMA process and requirements,
DOES MY COMMUNITY HAVE LIDAR?
Not all communities have LiDAR data available. Talk to your floodplain administrator to find out if your
community has LiDAR data.
To be used in a LOMA request, LiDAR data must meet or exceed the U.S. Geological Survey (USGS)
Quality Level 3 accuracy requirement. To learn more about this requirement, please use the USGS
LiDAR Base Specification Guide.
The USGS plans to collect high quality LiDAR data across the United States using a 3D Elevation
Program (3DEP). For more information on the 3DEP program and current USGS LiDAR availability,
WHEN LIDAR CANNOT BE USED
There are situations when LiDAR cannot be used in a LOMA request. These include applications involving
the following:
• Buildings or lots elevated using fill
• Buildings or lots in the regulatory floodway
• Buildings or lots in Coastal High Hazard Areas (Zone V, VE, or V1-V30)
• Buildings or lots in Zone AO, AR, or A99
• Buildings under construction. LiDAR would need to show that the lot or portion of the lot on which
building will be located is above the Base Flood Elevation (BFE)
• Conditional determinations
• Electronic LOMAs (eLOMAs)
• Potential violations identified through the LOMA process
• Physical changes to the flooding source/Special Flood Hazard Area that require revisions to the
Flood Insurance Rate Map
• Requests to supersede previously issued LOMAs based on certified elevation data
Additional information about LiDAR requirements for LOMAs is available in the
MT-1 Technical Guidance document.
WHAT NEEDS TO BE SUBMITTED WITH MY APPLICATION?
When requesting a LOMA using LiDAR data, you must submit a paper map or digital PDF that displays:
(1) an overlay of the LiDAR contours (lines of equal elevation), or
(2) an overlay of the LiDAR points (points with specific elevations).
Either overlay must include an aerial image of the building or lot with at least one street intersection
shown on the map.
The map must also have:
• Scale and North arrow
• Source of the LiDAR, including public website
address. LiDAR must be provided by a Federal,
State, or local government agency.
• Address or Assessor’s Parcel Number (APN)
for the building/lot
• LiDAR accuracy information
• Clearly identified building and/or lot boundaries
• Name, organization, and contact information
for the map overlay creator
(Does it meet Quality Level 3 standards?)
• Vertical Datum of elevation data (e.g., NAVD 88)
• Location of the data archive or metadata file
(must be available for independent verification
through a publicly available website or metadata)
• Aerial imagery that correctly represents the
footprint of the building
• Date the LiDAR was collected
Your floodplain administrator or a mapping professional can help you develop the map for your
application. For other requirements, please use the How to Request a Map Amendment Guide.
|
DECEMBER 2018
USING LIDAR FOR MAP AMENDMENTS
2
CALCULATING ELEVATIONS USING LIDAR
The lowest adjacent grade (LAG) for a building, or the lowest lot elevation (LLE) for a lot, will be compared
to the effective Base Flood Elevation (BFE) to determine the flood zone. If LAG/LLE is at or above the BFE
on the current flood map, FEMA can issue a removal determination. For buildings or lots that cannot be
removed from the high-risk zone using LiDAR, certified elevation data will be required for a standard LOMA
determination.
Using LiDAR Contours
For LOMA submittals that include LiDAR data contours, FEMA will subtract half the contour interval or
1 foot, whichever is greater, from the lowest contour closest to (but not going through) the building (to
determine the LAG) or the lot (to determine the LLE).
CALCULATING THE LOWEST GRADE (LAG)
1. Determine the closest contour lower than the building footprint.
2. Subtract 1/2 the contour interval or 1 ft., whichever is greater to determine the applicable LAG or Lowest Lot Elevation (LLE).
Elevation 802’
This structure is Out as Shown (OAS)
Requests where the FIRM data clearly
LAG would be 797’
(closest lower contour
shows the property/structure to be Out as
Shown are not eligible for LiDAR review.
of 798’ - 1’)
Elevation 800’
LAG would be 797’
(closest lower contour
of 798’ - 1’)
Elevation 798’
LAG would be 795’
(Will Need Field Survey) (closest
lower contour of 796’ - 1’)
Elevation 796’
Zone AE
Lake BFE = 796.2
|
DECEMBER 2018
USING LIDAR FOR MAP AMENDMENTS
3
Using LiDAR Point Data
For submittals that include LiDAR point data, FEMA will subtract 2 feet from the lowest point closest to the
building (to determine the LAG) or the lowest point on the lot (to determine the LLE). Multiple points must
cover the building/lot for this method.
•365.53
Zone AE
Lake BFE = 360.0
•369.09
•369.05
•369.31
LAG would be 360.77’
(lowest adjacent
point -2')
•362.85
•366.38
•367.99
•369.49
•371.34
•370.68
363.62•
364.94•
362.77•
•371.8
•373.18
367.68•
•374.35
•374.58
•374.56
•374.58
•371.57
•372.24
•370.11
WHERE DO I GO IF I NEED HELP?
To speak with a Map Specialist about the amendment process, contact the FEMA Map Information
eXchange (FMIX) at 877-FEMA-MAP (877-336-2627) or FEMAMapSpecialist@riskmapcds.com
|
DECEMBER 2018
USING LIDAR FOR MAP AMENDMENTS
4
No comments:
Post a Comment