Land Subject to Coastal Storm Flowage

Rebecca Haney Lealdon Langley Coastal Geologist Wetlands & Waterways MCZM MassDEP

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

•

Salisbury Scituate

Westport Nantucket

Storm Damage

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

King Tide

Scituate, 2016

Boston, 2016

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

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

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)

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”

FEMA Flood Zones

Flood Insurance Rate Maps

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.

msc.fema.gov/portal

Choose “Interactive Map”

to see complete LiMWA

Select

“Show

Contents of

Map”

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.

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

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.

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.

Function: Allow Flood

Waters to Spread

Over a Wide Area

Sediment transport reduces

energy and storm damage

Scituate Source: Google

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.

Reduced Function - Increased storm damage

Hull

Straits Pond, Hull, MA

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.

Obstructions to Flow: channelizes flood

water, increases velocity of water

Flow Channels: Findings from FEMA

Hurricane Sandy Report

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.

Impacts of Flow

Channels

Undermined house south of flow channel D.

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.

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.

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.

CES Best Management Practices

• Maintain the level of

the beach seaward

of the structure.

• Break the cycle of

bigger structures.

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.

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.

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.

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.

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.

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

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.

Case Study 3: Proposed Project in LSCSF

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

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

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

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.

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.

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

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