Floodways - The Original Intent

Cooperating Technical Partners Information Exchange

ASFPM Flood Science Center September 19, 2019

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ASFPM Mapping and Engineering Standards Committee

Cooperating Technical Partners Subcommittee

Co-chairs: • Brooke Seymour, P.E., CFM - bseymour@udfcd.org

Colorado's Urban Drainage and Flood Control District• Rita Weaver, P.E., CFM - rita.weaver@state.mn.us

Minnesota Department of Natural Resources

Goals:• Identify common concerns• Provide opportunities for information exchange• Identify training needs• Promote and document the value of CTPs

Agenda

Introduction - Alan Lulloff (ASFPM Flood Science Center)

Floodway Surcharge: History and Impacts - Alan Lulloff

Mapping Floodways: Basic, Better, NAI - Alan Lulloff & Dave Carlton (dkcarlton and associates)

Mapping Floodways: MN Best Practice - Ceil Strauss (MN DNR)

Managing Development in Floodways: Basic, Better, NAI - Alan Lulloff & Dave Carlton

Managing Development in Floodways: WI Best Practice - Chris Olds (WI DNR)

Questions/Discussion

FloodwaysThe Original Intent

Presented by:Alan R. Lulloff, P.E., CFMDave Carlton, P.E., CFM

AcknowledgementsAdvocates for Change

Larry Larson

Mark Riebau

Lynn Lovell

John Ivey

Brian Varella

Jeff Sickels

Del Schwalls

Bill Brown

Dave Carlton

Acknowledgementsfor this project

FEMA

Rhonda Montgomery Rick Sacbibit Rachael Sears

Advisory Committee

Mark Riebau Mark Forest Jerry Murphy Brian Varella Carey Johnson Dave Knipe Steve Story Heidi Hansen

One-foot surcharge floodway

What is this thing called surcharge?

What was the original intent?

Matching the original intent

Addressing Cumulative Impacts

Title 44 CFR Part 60, Section 59.1

“A floodway is defined as the channel of a river or other watercourse and the adjacent land areas that must be reservedin order to discharge the base flood without cumulatively increasing the water-surface elevation by more than a designated height.”

NFIP Floodway Definition

Title 44 CFR Part 60, Section 60.3

… the community shall

60.3 (d) (2) Select and adopt a regulatory floodway based on the principle that the area chosen for the regulatory floodway must be designed to carry the waters of the base flood, without increasing the water surface elevation of that flood more than one footat any point;

Equal Degree of Encroachment – Cumulative Impacts

Floodway Surcharge

Why was FW surcharge concept established?

James Goddard 1978 Report:

Origin and Rationale of Criterion Used in

Designating Floodways

Tennessee Valley

Why was FW surcharge concept established?

According to Goddard:

“It was to be a minimum criterion intended as a regional standard, recognizing that there were urbanizing areas …(with) existing development where … a much smaller rise might be appropriately considered.”

States that allow less of a surchargeWisconsin 0.00

Illinois 0.1 (measureable amt.)

Indiana 0.1 (measureable amt.)

Michigan 0.1 (measureable amt.)

New Jersey 0.2

Minnesota 0.5

Montana 0.5

Colorado 0.5

Quotes from some States that do not allow a measureable surcharge

Illinois –

“the overbank fp of most streams in state quite flat. A small increase can significantly expand the width of the fp. Unreasonable economically to allow any increase that subjects previously ‘safe’ structures to flood waters.”

Indiana –

“there are few topographic restraints on development in Indiana, so there is no real need to view floodplains as the only developable area.”

Quotes from some States that do not allow a measureable surcharge

Community established higher floodway standards

Charlotte/ Mecklenburg, NC

Future conditions

0.1 ft Surcharge Floodway

ASFPM Floodway Study 2013

Comparison between1 ft & 0 surcharge

Stream

Avg. width Decrease

(%)

Velocity Increase (ft/sec)

Average Velocity Inc. (%)

Increase floodplain

(%)Pine Creek 59 2.28 to 3.69 62 6

Patterson Creek 68 1.11 to 1.61 45

Stevens Branch 39 4.98 to 5.82 18

Sugar River 50 1.57 to 2.07 32 14

Four Mile Creek 43 2.58 to 3.25 26

Cypress Creek (100) 48 1.92 to 2.46 22

Cypress Creek (172) 64 1.18 to 1.71 45

Plum Creek 32 7.15 to 8.31 16

Avg. all 8 reaches 50 2.85 to 3.62 33 10

Stream

Avg. width Decrease

(%)

Average Velocity Inc. (%)

Increase floodplain

(%)

Avg. all 8 reaches 50 33 10

Comparison between1 ft & 0 surcharge

One-foot surcharge FWs enable filling half the natural FW

Effects of Encroachment due to Surcharge

Floodwaters rise to higher levels causing properties that were once flood‐free to now be flood‐prone

Rise in floodwaters increases velocity of flood waters and therefore increases the potential to erode stream banks

Floodplain filling reduces floodplain’s ability to store water

Poll Question

Floodways with a one-foot surcharge pinch-in the natural floodway by what percentage?

- 10%

- 20%

- 33%

- 50%

FEMA tote at ASFPM in Cleveland

Potential Impacts of Fill in the Natural Floodway

Hydraulic/Hydrologic Impacts

Increased channel velocities

Higher hazard (depth & velocity)

Aggradation –raised water surface

Degradation –bank failure

Review of guidelines and CFR

Guidelines – FEMA Nov 2016

Floodway Coordination Meeting

CFR – 60.3 (d) (2) the community shall select and adopt a regulatory floodway

(Minnesota best practice)

Minnesota Floodway Best Practices

September 19, 2019

“The limits of the floodway shall be designated so that permissible encroachments on the floodplain will not cause an increase in stage of the regional flood of more than 0.5 feet in any one reach or for the cumulative effect of several reaches of a watercourse.  If the increase in flood stage will materially increase the flood damage potential, the commissioner may require that such increases be less than 0.5 feet.”

Interpreted as: No (0.00’ foot) increase allowed if existing insurable structures impacted.

Legal Background ‐ MN Rules adopted 1970

MN Rules 6120.5700, Subp. 4, A.

• Technical guidance on how to meet the 0.5’ maximum stage increase

• Encouraged designating entire floodplain as floodway

• Process for community selection of floodway; community designates floodway based on their needs, but it’s verified to not cause more than 0.5’ increase or impact existing buildings 

1977 Technical Report on Floodways

Example of Floodway in Community With Existing Development

• Example 1986 Flood Boundary and Floodway (FBFW) map 

• Floodplain all floodway where possible

• Mainly current development shown as flood fringe and rest of floodplain as floodway

Note on FBFW maps:• Floodway is white with heavy dashed boundary

• Flood fringe is gray shading

•Many communities and watershed districts have community or district‐wide modeling, and enforce higher standards 

• Local studies are leveraged and used as supporting data in updated FEMA Flood Insurance Rate Maps

•Some studies assume storage areas will be retained (i.e., XP‐SWMM)

•Those storage areas are shown as “Floodway” on the FIRMs and are administered with the more restrictive floodway ordinance standards.

More Recent Use of Floodway For Modeling

Thank You!

Ceil StraussCeil.Strauss@state.mn.us

651‐259‐5713

Basic

FEMA G&S FW Coordination Mtg.

CFR Have community select a

floodway – i.e. a surcharge.

Promote zero-surcharge FW---------------------------

Require community to notify owners if structures are impacted (similar to CLOMR)

Better

Risk Assessment Provide a future conditions (fully

encroached) map that shows the additional inundation caused by the surcharge

Provide zero-surcharge FWs as the default

Allow a surcharge if no structures are impacted

Require freeboard for new structures in flood fringe

Matching Original Intent -Mapping

Matching Original Intent -MappingNo Adverse Impact

Require easements be obtained from property owners impacted by the surcharge (WI Best Practice)

Risk Assessments (e.g. HAZUS) should include both existing (BFE) and future conditions (BFE + surcharge) so that community can see the potential additional damages caused by new development as fringe is filled

In your opinion, if made aware of the impacts – what percentage of communities would opt for zero-surcharge floodways?

- No communities would opt for a zero-surcharge floodway

- 10% of communities

- 20% of communities

- 30% of communities

- 50% of communities

Poll Question

In your opinion, if made aware of the impacts – what percentage of communities would opt for zero-surcharge floodways?

Poll Results

Managing Development in Floodways:Wisconsin Code

Chris OldsState Floodplain Engineer

Wisconsin Department of Natural Resources

Floodway Definitions

• State Statute 87.30

• Administrative Code NR 116

• Model Floodplain Ordinance

• LOMC Guidance

Statute 87.30

NR 116

NR 116

NR 116

NR 116

State Model Ordinance

Easement Example

WI DNR LOMC Guidance

Chris OldsWisconsin Department of Natural ResourcesChristopher.Olds@Wisconsin.gov608-266-5606

Require cumulative impact analysis for proposed encroachments

Based upon legal precedent concept

Consistent with historic FEMA Community Assistance Series No. 4 (1974)

Managing Development in the Floodway ---- Better

61

Use better tools to analyze the impacts

2D models

Unsteady models

Limit increases in velocity in addition to loss of conveyance

Managing Development in the Floodway ---- Better

Best Practice City of Brevard, Transylvania County, NC

No Adverse Impact certification instead of a No Rise certification

No increase in elevation, velocity or erosion

Managing Development in the FW No Adverse Impact

Loss of flood storage should be included in the analysis

Impacts on floodplain habitat should be analyzed (ESA)

Managing Development in the FW No Adverse Impact

ASFPM No Adverse ImpactHow-to Guides

Questions&

DiscussionAlan Lulloff, PE, CFMalan@floods.org

Dave Carlton, P.E., CFMdave@dkcarlton.com

Ceil Strauss, CFMceil.strauss@state.mn.us

Chris Olds, P.E.christopher.olds@wisconsin.gov

ASFPM Flood Science Center

Cooperating Technical Partners

Information Exchange

Poll Question

Please rate this webinar.

Future CTP Webinar Topics Poll

https://www.surveymonkey.com/r/CTP-Webinar-Topics-Poll-2019

Check your chat panel for this link.

• Certified Floodplain Managers are eligible for 1 CEC for participating in this webinar.

• You must have registered individually and indicated you are a CFM at time of registration.

• Eligibility for CEC is dependent on your participation in poll questions and time spent viewing the webinar, as determined by the webinar software.

• Attending this webinar in a group setting or only viewing the recording is NOT eligible for CEC.

Continuing Education Credits

• To suggest future CTP webinar topics, please contact Alan Lulloff at alan@floods.org or type a suggested topic into the Questions panel today.

• ASFPM CFM CECs will be automatically applied.

• Certificates of Attendance will be emailed, please contact cfm@floods.org with any certificate issues.

• Follow-up email with link to slides and recording will be sent next week

Thank You for Joining Us!

Closing Comments