land subject to coastal storm flowage...• land subject to coastal storm flowage: means land...
TRANSCRIPT
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Land Subject to Coastal Storm Flowage
Rebecca Haney Lealdon Langley Coastal Geologist Wetlands & Waterways MCZM MassDEP
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Why do we need these regs?
• Prevent/reduce flood damage, decrease repetitive loss
claims, protect public safety and infrastructure
• Proposed regulations apply similar standard that has been in
effect for Coastal Beaches, Dunes, Land Under the Ocean,
Barrier Beaches, and Coastal Banks to LSCSF that overlaps
these resource areas AND to LSCSF outside of these other
resource areas
• To advance resiliency to sea level rise and provide
opportunity for climate change adaptation
• Provides standards and guidance in an area that is currently
lacking
•
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Salisbury Scituate
Westport Nantucket
Storm Damage
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Status of Effort
• Building Code – Public Hearings scheduled for March 7,
Boston and March 14, Springfield
• Adds 1‘ freeboard to A zones, retains revisions adopted in
2009 for freeboard in V-zones, pile supported foundations
in Coastal Dune when determined by issuing authority to
be significant to storm damage prevention and flood
control
• Coastal A Zone Maps – technical review by FEMA. FEMA
will update the official maps (NFHL)
• Stakeholder Group will re-convene to review draft
regulations
• MassDEP will conduct public hearings and commence public
comment to promulgate regulations
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King Tide
Scituate, 2016
Boston, 2016
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These figures do not include uninsured damages--damages that were not insured
because the property did not have a flood insurance policy through the NFIP or
because the damage was not covered under the policy (e.g., deductible limits,
damage above the coverage amount). Additionally, damage from coastal erosion
that is not directly connected with a flood event is not covered by the NFIP.
Total claims:
Over $369 million
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Definitions/Terminology
• Land subject to coastal
storm flowage: means land
subject to any inundation
caused by coastal storms
up to and including that
caused by the 100-year
storm, surge of record or
storm of record, whichever
is greater. (310 CMR
10.04)
• 100 year storm = storm
having a 1% chance of
being equaled or
exceeded in a given year.
Marshfield
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Definitions/Terminology
• Special Flood Hazard Area means the area of land in the
flood plain that is subject to a 1% chance of flooding in
any given year as determined by the best available
information, including, but not limited to, the currently
effective or preliminary Federal Emergency Management
Agency (FEMA) Flood Insurance Study or Rate Map
(except for any portion of a preliminary map that is the
subject of an appeal to FEMA) for Land Subject to
Coastal Storm Flowage, the Velocity Zone as defined in
310 CMR 10.04, … (emphasis added)
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FEMA Flood Zone Definitions
• Zone VE (V1-30) – Areas of 100-year coastal flood with velocity
waves
Wave height 3 feet or greater
Wave runup depth 3 feet or greater
Within primary frontal dune (first dune landward of the beach)
• Zone AE (A1-30) – Areas of 100-year flood; flood elevations
May be coastal or riverine
Coastal can contain up to 2.9 feet wave height
Coastal flood elevations at top of wave envelope
• Coastal A Zone (MoWA) – Portion of the A Zone with 1.5 – 3.0’
waves.
Separated from the rest of the A Zone by the LiMWA
• Zone AO – “Overwash” areas with flow depths of 1 to 3 feet
Generally coastal with sloping ground
Flow velocities can vary greatly
Flow paths are typically not well defined
• Zone A – Areas of 100-year flood; NO flood elevations given
• Shaded Zone X (B) – Areas of 500-year flood
• Unshaded Zone X (C) – “Areas of minimal flooding”
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FEMA Flood Zones
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Flood Insurance Rate Maps
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Coastal A Zones
• Subset of the A Zone, where wave heights are 1.5’ – 3’
• Separated from the rest of the A Zone by the Limit of
Moderate Wave Action (LiMWA)
• FEMA has determined that buildings built to traditional A
Zone standards receive structural damage under these
conditions (FEMA CCM 2011).
• FEMA FIRMs only show portions of the LiMWA due to
overlap with other boundary lines.
• CZM and DCR updated the LiMWA in MA based on FEMA
policy issued in December 2013.
• FEMA is updating the National Flood Hazard Layer,
available on the Map Service Center with the full LiMWA.
• There are currently no regulatory requirements specific to
Coastal A Zones.
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msc.fema.gov/portal
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Choose “Interactive Map”
to see complete LiMWA
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Select
“Show
Contents of
Map”
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MassDEP and Conservation
Commissions should:
• Rely on MGL Ch 131, Sect 40 to establish
authority. “No person shall remove, fill, dredge
or alter any...land subject to… coastal storm
flowage...”
• Presume that LSCSF performs functions for the
storm damage prevention and flood control
interests
• Assess how LSCSF functions at a project site
• Consider whether the project adversely impacts
these functions and interests, and
• Impose conditions to contribute to the protection
of the interests.
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LSCSF functions to:
• Slow down flood waters, allow them to flow across a natural
landform surface, and provide frictional resistance, thereby
reducing their energy and destruction potential.
• When flood waters encounter obstructions, channelization of
flood waters and storm-wave overwash occurs, increasing
velocity and volume of flow to adjacent or landward areas.
Scituate
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LSCSF Function
• Allowing water to flow
unimpeded under elevated
buildings allows energy
dissipation.
• Solid foundations deflect, reflect
or redirect waves and flood
water, channeling more water
flowing at higher velocities onto
adjacent resource areas,
properties and public roads.
• Elevating the lowest structural
member above the FEMA Base
Flood Elevation to account for
sea level rise increases storm
damage and flood control
functions of LSCSF.
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Function: Slow Down Flood Water
Rockport
Characteristics important for this function:
• Slope, soil characteristics, vegetation, erodability, permeability.
• Reduces energy and destruction potential, protecting landward
areas.
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Function: Allow Flood
Waters to Spread
Over a Wide Area
Sediment transport reduces
energy and storm damage
Scituate Source: Google
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LSCSF functions to:
• Allow flood waters to be
detained, absorbed into
the ground, or
evaporated into the
atmosphere.
• Protect the land from
storm erosion by
providing a substrate for
vegetation that helps to
stabilize sediments and
slow down floodwater.
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Reduced Function - Increased storm damage
Hull
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Straits Pond, Hull, MA
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Projects can diminish LSCSF functions:
Buildings on solid foundations and impervious surfaces in the
floodplain may channel flood waters, with a higher velocity of
flow to adjacent areas .
Reducing vegetation and pervious areas reduces surfaces that
can detain, absorb, slow, or evaporate waters, thereby
changing the drainage characteristics in a manner that could
cause increased flood damage on adjacent properties.
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Obstructions to Flow: channelizes flood
water, increases velocity of water
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Flow Channels: Findings from FEMA
Hurricane Sandy Report
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Impacts of Flow
Channelization
House washed into the bay at the site of flow channel A
Undermined house with damaged foundation
between flow channels B and C.
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Impacts of Flow
Channels
Undermined house south of flow channel D.
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Coastal Engineering Structures
• Coastal engineering
structures often deflect,
reflect and redirect storm
waves, affecting adjacent
properties and landward
areas with wave energy,
overwash and floodwaters.
• Erosion occurs seaward of
the structures as a result
of the wave reflection, and
overtopping damages
buildings and causes
erosion landward of
structures.
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FEMA Hurricane Sandy Findings
Buildings within 10-20
feet of shore-parallel
erosion control structures
(e.g., seawall, bulkhead,
revetment), overtopped
by storm waves and/or
surge during Hurricane
Sandy were damaged,
even when the erosion
control structure
survived.
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Coastal Engineering Structures
Best management practices should be used to reduce
wave reflection, overtopping, and damage landward of
and adjacent to coastal engineering structures.
•Keep the CES as
far landward as
possible
•Address sources of
upland runoff.
•Sloping structures
dissipate wave
energy better than
vertical structures.
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CES Best Management Practices
• Maintain the level of
the beach seaward
of the structure.
• Break the cycle of
bigger structures.
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CES Best Management Practices
• Minimize end
effects on adjacent
properties by
pulling the
structure back 15-
20’ from the
property line.
• Transition to
adjacent
properties.
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LSCSF: Hydraulically
Restricted Areas
MARSH
OCEAN
Filling areas where water flow
is restricted, such as where
pipes, culverts, dikes, or other
physical restrictions limit water
flow may require
compensatory flood storage.
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Projects can diminish LSCSF functions:
• Dredging or the removal of materials
within the coastal floodplain which results
in greater water depth, allowing storm
waves to break farther inland and to
impact upland and wetland resource
areas.
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Case Study 1: Proposed Project in LSCSF
Proposed project: new house on a solid foundation with a
paved driveway. Solid foundation may reflect waves and
channelize flood waters around the foundation onto
adjacent properties. Increased volume and velocity of
water may increase storm damage to dwellings and town
road landward of the site.
Background:
•Site mapped as A
Zone on the FIRM
• BFE 13, ground
elevation 10.
• Resource area
LSCSF, buffer zone to
coastal bank.
Location of
proposed
house.
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Alternatives to Reduce Impacts
• Minimize the project footprint
• Elevating the building on open
pilings would allow flood water to
flow unobstructed under the
building (include sea level rise).
• Minimize removal of natural
vegetation. Avoid or minimize
lawn area.
• Prefer pervious surfaces (gravel,
shell, pea stone) over new solid
surfaces (pavement, concrete,
pavers).
• Avoid fill that displaces flood
storage capacity or redirects flow
onto adjacent properties.
• Avoid new fences or
retaining walls that
would channelize
moving water.
• Note: Building Code
would require solid
foundation with
hydraulic openings.
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Case Study 2: Proposed Project in LSCSF
Proposed: House on a solid
foundations with paved
driveway.
Recommended: use of the
existing unpaved road, or use
of gravel, pea stone or shell to
improve infiltration of
floodwater.
Building Code: requires solid
foundation with hydraulic
openings.
Background:
• A Zone, BFE 2’ above
grade.
• Resource area: LSCSF
Location of
proposed
house
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Case Study 3: Proposed Project in LSCSF
Site location
Background
•Velocity Flood
Zone
•Existing house
at grade
•Proposed
project involves
tearing down
the existing
house and
building a new
one.
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Case Study 3: Proposed Project in LSCSF
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The project site involves which of the following resource
areas?
A) Coastal dune
B) Coastal beach
C) Land subject to coastal storm flowage
D) Barrier beach
E) All of the above
F) A, C and D
Question # 1
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Question # 2
The new house should be on:
A) At grade foundation with full basement
B) Open pilings two feet above the Base Flood Elevation for
Building Code
C) Open pilings two feet above the Base Flood Elevation and
two feet above the adjacent dune
D) At grade foundation without a basement
E) Open pilings at the Base Flood Elevation for Building Code
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Question # 3
Improving the new structure’s climate resiliency could involve:
A) Re-vegetating coastal dune at an on-site location to mitigate
for any coastal dune newly impacted by enlarging the structure
B) Raising the structure’s foundation elevation to comply with the
Building Code
C) Moving the structure further landward and placing it on a pile
foundation
D) Moving the structure further landward, placing it on a pile
foundation above Base Flood Elevation, 2’ above the adjacent
coastal dune and enhancing the primary dune seaward of the
house
E) Constructing a revetment seaward of the structure
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Summary
• Storm damages are
increasing in lower frequency
events.
• Storm of record can affect
greater area than the mapped
flood zones.
• More than half the buildings in
NY City affected by Sandy
were outside the mapped
flood zones.
• Use best available information
regarding actual extent of
flooding in coastal storms.
• 25% of all NFIP claims occur
outside mapped flood zones.
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Take Home Message:
• Authority to regulate LSCSF established in law.
• Presume that LSCSF protects storm damage
prevention and flood control interests
• Assessing how LSCSF functions at a project site
requires use of FEMA resources (FIRM and
profiles), site plans, site observations,
knowledge of project design, and knowledge of
principles we discussed today.
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Take Home Message:
Considering potential adverse impacts and
developing conditions requires evaluating:
• Height above Base Flood Elevation
• Type of foundation
• Vegetation condition and changes
• Pervious and Impervious surfaces
• Grade changes
• Proximity to other structures
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References
• FEMA Mitigation Assessment Team Report:
Hurricane Sandy in New York and New Jersey
(November 2013)
• Sea Level Rise: Understanding and Applying
Trends and Future Scenarios for Analysis and
Planning.
• CZM StormSmart Coasts:
mass.gov/czm/stormsmart
– CZM Coastal Landscaping Website
– StormSmart Properties Fact Sheets