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Norfolk and the RegionFLOODING

Kristen M. Lentz, P.E., Acting Director of Public Works8/25/2010

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Purpose

– Section I• Scientific overview of flooding • Future projections• Potential consequences

– Section 2• Flood mitigation tools

– Section 3• Norfolk’s Flood Mitigation Program

– Activities currently underway – Recommended program expansion– Policy considerations, next steps and

conclusions

Provide a briefing on an important issue for Norfolk and the region

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Acknowledgements• Numerous individuals and organizations provided valuable

information and input into this presentation including:

– Norfolk Residents and Businesses

– U.S. Army Corps of Engineers (ACOE)

– Virginia Institute of Marine Sciences (VIMS)

– Hampton Roads Planning District Commission (HRPDC)

– Fugro World Wide

– Multiple City Departments

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Section 1

Scientific Overview of FloodingFuture Projections

Potential Consequences

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Why Flooding OccursIn Norfolk, flooding is caused by rainfall, tides or

a combination of both

Rainfall Flooding– Rain intensity exceeds capacity of the storm drain system

Tidal FloodingGreater challenge and primary focus of this presentation

– Caused by tidal variations and storm surges – Directly related to land elevation and proximity

to coastline– Can exacerbate rainfall flooding

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Understanding TailwaterWhere Precipitation Runoff Meets Tidal Waters

Precipitation

Rain Water

Tidal Water

Drainage Pipe Opening

Ground

Runoff Tailwater

TYPICAL SUBMERGED OR PARTIALLY SUBMERGED STORM WATER OUTFALLTailwater phenomena causes rainfall and tidal flooding to be inextricably linked.

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Understanding Storm Intensity Terminology

• Scientists describe a rainfall event or a tidal storm by its recurrence interval, which is the probability it will occur at least once in a given span of time

• A 100-year storm (either tidal or rainfall):• Has a probability of occurring once every 100 years• 1% chance of happening in any given year • Since these are probabilities, more than one 100-year storm can

occur during any given period of time

• A lower intensity storm event recurs more often than a higher intensity event

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Storm Intensity and Norfolk’s Drainage System

• Largely over 60 years old and primarily designed for the 2-year rainfall storm

• Consists of:– 1.8 million linear feet of pipes– 28,100 structures– 260,832 linear feet of ditches– 13 City maintained storm water ponds– 9 underpass pumping facilities– the Downtown floodwall and its pumping station

• Since 2000, new and replacement facilities have been designed for 10-year storm

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Understanding Flood Elevation Terminology

• Using data from previous storm events, scientists predict the elevation of flood waters for storms of various intensities

• Base Flood Elevation- is the predicted elevation of the tide, not including any wind-driven wave action or rainfall

• The Federal Emergency Management Agency (FEMA) produces maps that show the predicted 100-year base flood elevation for Norfolk

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Flooding Datum Basics• The 1988 North American Vertical Datum (NAVD 88) is

the standard reference point used for measuring tide elevations

• Many other datums exist for various applications; however, NAVD 88 is the standard for FEMA’s Flood Insurance Rate Maps (FIRM), National Oceanic and Atmospheric Administration (NOAA) and Norfolk tide gauges, elevation certificates and other property surveys

• At Sewells Point– Normal high tide is about 1.1’ NAVD 88– Normal low tide is about -1.5’ NAVD 88

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Hampton Roads’ Major Tidal EventsThis chart shows the 7 most significant tidal events that have occurred in the last 80

years. Note that 4 of the 7 occurred in the last 10 years.

8.16

4.39

6.25

5.13

4.22

6.08

7.26

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

1933Hurricane

1960 AshWed Storm

1998 TwinNor'easter

2003Hurricane

Isabel

2006NovemberNor'easter

2008September

Storm

2009NovemberNor'easter

7.6ft (2009 100-year Flood Plain)

NA

VD88

(FEE

T)N

AVD

88 (F

EET)

Normal High Tide

Storm Tide Elevations at Sewells Point

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Sewells Point History• Since 1930, relative mean sea level at Sewells Point has been documented

to have risen 14.5 inches • Rate of sea level rise has been increasing in recent years and is projected

by some to continue increasing

(NOAA, Tides and Currents, Sea Level Trends, 2010)

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Tidal Flooding Projections

• Tidal flooding has occurred with greater frequency in recent years – a trend that can be expected to continue due to several factors:

– Weather events of greater severity (related to increased ocean water temperatures)

– Sea level rise

– Land subsidence (land sinking)

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Land Subsidence• Land subsidence is

occurring faster in Hampton Roads than surrounding areas

•Filled areas sink faster than others

•Areas near the Chesapeake Bay impact crater are shifting

•Average rate of subsidence in Hampton Roads is estimated by the Chesapeake Bay Program’s Scientific and Technical Advisory Committee at 0.57 inches per decade

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Relative Sea Level Rise

Sea Level Rise

• Relative Sea Level = Sea Level Rise + Land Subsidence

• Among Scientists there is a wide range of future sea level rise projections

• Mid-range future projections of Relative Sea Level Rise for Hampton Roads are 2 - 4 inchesper decade

Land Subsidence

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In 2009 FEMA increased Norfolk’s base flood elevation by 0.3 feet over their 1980 prediction

FEMA Flood Hazard MapFEMA Flood Hazard Map

2009 100-year Flood Elevation 7.6 FT (NAVD88)

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U. S. Relative Sea Level ChangeHampton Roads’ rise has been the greatest of any location on the east coast

SewellsPoint

0.174in/yr

EPA 2008

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Potential Long-Term Impacts of Relative Sea Level Rise

• More frequent and severe flooding• Flood insurance required for more properties and at

higher cost• Public facilities and infrastructure more susceptible to

flooding• Transportation disruptions• Reduction in suitable land for development/redevelopment • Environmental effects including loss of wetlands and

wildlife habitat• Businesses and residents may relocate inland from

coastal areas

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Flooding- A Regional ChallengeFlooding has been recognized as an important regional issue for Hampton Roads

– ODU’s Dr. James Koch is calling upon local leaders to make flooding a priority issue. “ Flooding, then may be the issue of the 21st century for Hampton Roads. Yes, our transportation challenges are immense, but even the best roads are of no use ifthey are under water.” (Daily Press Editorial January 2010)

– Agencies such as the U.S. Navy and businesses such as Northrop - Grumman have already realized the importance of this issue and have hired consultants to help them understand how relative sea level rise could impact the future of their organizations. Such information will be used in crafting future business plans.

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Section 2

Flood Mitigation Tools

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Flood Mitigation Tools – General Overview

• Improve conditions, but cannot guarantee against all future flooding

• Many types with widely ranging costs and results

• Different forms – Physical– Plans or regulations– Informational– Educational

• More than one tool can be utilized for a single area

• Norfolk has implemented many of the available tools in varying degrees and locations

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Flood Mitigation Tools –Precipitation Flooding

• Storm Water Ponds -Create additional rainfall drainage system capacity by providing storage that slows the flow of runoff

• Storm Pump stations –add capacity by carrying rainfall out faster

• Larger pipes or ditches– Carry rainfall out faster– Allow tide in faster

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Flood Mitigation Tools – Tide Gates • Tide gates at the end of storm drain pipes keep the tide out

– Provide flood protection if there is no precipitation, however…. – Rainfall runoff backs up and can cause flooding deeper than the

tidal flooding – Often malfunction and are maintenance intensive

• Clogging with debris• Salt water corrodes metal and deteriorates rubber seals

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Flood Mitigation Tools –Major Structures

• Floodwalls and levees– Can provide continuous tidal protection– Require pump stations to pump rainfall out– Significant visual and environmental impacts – Costly

Seawall: Galveston, Texas

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Flood Mitigation Tools – Flood Gates•Permanent facility that provides temporary protection only as needed •Located at entrances to waterways

•Allow boat traffic except when activated •Require pump stations to address rainfall

Storm Surge Gate: The Netherlands

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Flood Mitigation Tools –Design Considerations for Major Structures

Including Flood Walls and Flood Gates

Multiple design considerations must be investigated in order to determine whether a major flood control structure is feasible, and, if so, its estimated cost

1. Width of span2. Depth of water and boat traffic3. Storm design height4. Sub-surface soil conditions for seepage and support5. Existing underwater structures/remnants 6. How structure affects water flow process (scouring effect)7. Protection of adjacent areas 8. Storage capacity for rainfall / pumping station9. Environmental impacts and permitting

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Flood Mitigation Tools –Inflatable Dams

• A relatively new type of flood gate for use in a coastal environment with the potential for significantly lower costs

• Water or air filled bladder that is inflated by a pump station when tidal events are expected

• Requires a concrete support sill or foundation with structural considerations similar to traditional flood gates

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Flood Mitigation Tools –Shoreline Protection

• Sand dunes, beaches, wetlands or living shorelines can be constructed or expanded to protect coastal properties

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Flood Mitigation Tools –Adaptation of Structures

• Requirements that new facilities be built above the 100-year flood plain or another defined elevation– Finished floors– Parking areas– Roads

• Programs to raise existing structures

• Purchase and demolition of flood prone structures

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Flood Mitigation Tools – Plans and Regulations

• Comprehensive land-use plans – Optimize the use of flood-prone properties

• Parks and public amenities adjacent to waterways • Enhance public access to rivers, bays and lakes• Potential to raise property values for all rather than a few• Opportunity to improve environment by creating water

quality buffers and wildlife habitat

– Minimize the impact of flooding• Leave flood-prone properties undeveloped

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Flood Mitigation Tools – Plans and Regulations

• Zoning can be used to reduce the susceptibility of future development to flooding through regulations that address

• Finished floor elevations• Land use densities • Lot sizes• Land-to-building ratios

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Flood Mitigation Tools – Public Information and Notification

• Public information, warnings and notifications can be highly effective and relatively inexpensive mitigation tools

– Timely notice of expected higher tides

– Hazards of driving through flood waters

– Information regarding higher elevation roadways

– Shelter Locations

– Evacuation requests and routes

• Information and notification can utilize one or more • Brochures• Broadcast media• Reverse 911, or similar cellular service calls• Internet • Physical signs and barriers

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Flood Mitigation Tools – Public Education

• Newer residents, visitors and tourists may not be aware of flooding risks. We can educate them on – Tips for protecting property, such as identifying

appropriate places for parking vehicles during flooding events

– The risks to garages, sheds and basements and other personal property located below the home’s finished floor

• All residents need to be reminded periodically– Value of flood insurance, even for those outside of the

100 year flood plain

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Section 3Norfolk’s Flood Mitigation Program

•Current Program Overview•Recommended Program Expansion •Policy Considerations, Next Steps and Conclusions

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Norfolk’s Current Flood Mitigation Program

• Consists primarily of:

– Federal Assistance Programs and Projects

– Maintenance of Existing Storm Water System

– Flood mitigation projects that respond to problems and fit within the city’s approach and cost-benefit funding strategies

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Flood Reduction Projects CIP - 5 Year Plan

FY11 FY12 FY13 FY14 FY15 Total

$1.45

.60

.95

1.50

1.85

TOTAL $6.35 $6.35 $6.35 $6.35 $6.35 $31.75

Neighborhood Flood Reduction Program

$1.45 $1.45 $1.45 $1.45 $7.25

Storm Water Quality Improvement Program

.60

.95

1.50

1.85

Storm Water Facility Improvement Program

3.00.60.60.60

.95 4.75

1.50

.95

1.85

.95

1.50

1.85

1.50

1.85

7.50

9.25

Street Flooding Citywide

Fairmount Park Street & Drainage Improvements

* in millions

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Current Program Overview –The National Flood Insurance Program

(NFIP)• Norfolk participates in the NFIP which is a federal program enabling

property owners in member localities to purchase private flood insurance at subsidized rates based on flood insurance rate maps(FIRM) identifying 100-year flood plain boundary

• As a result of our voluntary participation in the Community Rating Program, the federal government provides a 5% reduction in floodinsurance rates in Norfolk

– Norfolk requires the finished floors of all new structures to be at least 1 foot above the 100-year base flood elevation, but the finished floor elevations of many older structures are lower

– City sends letters annually recommending the purchase of flood insurance for all properties in the vicinity of previous flood insurance claims

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Current Program Overview –FEMA’s Hazard Mitigation Program

• Provides limited funding to address repetitive loss properties which are defined as residential properties covered under a NFIP floodinsurance policy that have had:– At least four NFIP claim payments exceeding $5,000 each, or– Two separate claim payments that, when totaled, exceed the

market value of the building

• Funds can be applied to – Raising structures– Acquiring property

• Over the last 5 years, utilized by Norfolk to raise the finished floor of 24 structures (out of 148 applications) at a cost of $3.5 million (average of $146,000 per property)– Residents are required to contribute 5% of the cost of raising the

structure

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Repetitive Flooding Loss Sites

Repetitive FEMA Claim Sites

Raised Homes through FEMA Grants

Repetitive Loss is defined as a residential property covered under a NFIP flood insurance policy that has:• At least four NFIP claim payments exceeding $5,000 each OR• Two separate claims payments that, when totaled, exceeded the market value of the building.

Flood-prone AreasWilloughbyEast Ocean ViewLarrymore LawnsThe Hague/GhentColonial Place/RiverviewInglesideLarchmont/EdgewaterLochaven/MeadowbrookLambert’s PointLafayette/WinonaSpartan Village

Willoughby

East Ocean View

Larrymore LawnsLockhaven/Meadowbrook

Larchmont/Edgewater

Colonial Place/RiverviewLambert’s Point

The Hague/Ghent

Ingleside

Lafayette/Winona

Spartan Village

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Current Program Overview –Downtown Floodwall and Pumping Station

• The City’s Downtown floodwall, gates and pumping station were built in the late 1960’s by the U.S. Army Corps of Engineers to protect approximately 100 acres of the Downtown Business District from tidal flooding. They have performed well during the November 2009 Nor’easter and other events

• The pump station is needed to pump out rain water that would otherwise be held in by the flood wall

• The floodwall is currently being evaluated for recertification by FEMA

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City Hall Ave - 1962

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Flood Mitigation Projects Currently Underway

• Cleaning and rehabilitation of large drainage lines to improve drainage – Norfolk State University area pipes that drain Spartan Village – Tidewater Drive area by Ruffner Middle School– The Hague – Haven Creek

• Raising the roads to reduce tidal flooding– Bourbon Street – Richmond and Surrey Crescents

• Extend outfall pipes and install pumping equipment at 15th and Lea View

• Replacing the Masons Creek culvert

• Bulkhead replacement in Winona

• Living Shoreline Projects– Knitting Mill Creek– Haven Creek

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Norfolk’s Future Flood Mitigation Program

• An expansion of our existing flood mitigation program is needed to address our increasing coastal flooding challenges– Proactive and strategic– Long term project implementation plan (20 yrs) that

includes project prioritization and funding mechanisms

– Based upon a city-wide analysis of needs and cost effectiveness of projects

– The City has hired Fugro, an internationally experienced coastal engineering firm headquartered in the Netherlands to perform the city-wide analysis and assist us in developing the plan

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City-Wide Flooding Analysis

• Information on flood depths is needed to determine the best mitigation tools for an area

• Fugro is creating a model that forecasts flooding conditions throughout the City based on tide elevation data– Installed 4 additional tide gauges throughout the City

to provide better water surface elevation data – Utilized Light Detection and Ranging (LIDAR)

mapping to provide more frequent ground surface elevation data

• Model to be completed early 2011

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Tide Gauge Locations

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LIDAR vs. Spot Elevation Mapping

– LIDAR (Light Detection and Ranging) mapping provides 70 times asmany elevation points as typical aerial mapping

– Norfolk obtained LIDAR mapping data in 2009 – Provides basis for more accurately forecasting flood depths– HRPDC and scientific and engineering communities are encouraging

all Hampton Roads localities to obtain LIDAR data

LIDAR : 251.8 million elevation points city-wide

Older spot elevation techniques: 3.6 million points city-wide

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Development of an Expanded Flood Mitigation Program

• Using the modeling information, an alternatives evaluation will be performed for various levels of flood protection – Cost of implementing the flood mitigation tools– Damage repair costs avoided– General economic impacts

• Recommend– prioritization of projects/activities – a long-term implementation plan with associated funding

mechanisms

Consultant to complete study and proposed plan by end of 2011

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Focused Study Areas

• Due to unique geographical characteristics, three areas were identified for focused studies to be completed by the end of 2010– The Hague– Pretty Lake– Spartan Village/East Brambleton Area

• Study results to be evaluated for potential preliminary design inclusion in the FY12 CIP

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Recommended City Council Action• Extensive policy level discussions are needed prior to project driven

decisions

• Policy considerations need to include:– When and how to determine the acquisition of flood-prone properties– Adoption of adjustments to zoning regulations– City administration identifying for City Council approval alternative

financing options such as special taxing districts– Prioritization of criteria for major flood improvement projects

• City Council should also consider establishment or appointment of a Flood Management Advisory Committee; with the Mayor and another member of Council, city staff, and members of the publicwith interest and expertise to contribute to the effort of advising the City on best practices. The committee would not be involved in establishing priorities or specific projects.

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Federal Funding Availability

• Flood Damage Reduction – Nonstructural – Corps will study under a 50/50 cost share flooding problems

and potential nonstructural solutions

• Flood Damage Reduction - Structural, Section 205 – $7 million maximum project size– Current federal fiscal year funding nationwide is $50 million– If project meets federal criteria, is approved through a feasibility study,

and funding is available, the Corps may participate in completing the design and construction of the project at a 65/35 Corps/City cost share

• Larger flood control projects require U.S. Congressional appropriations (earmarks)

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Funding Strategies • An expanded flood mitigation program will

require funding on a long-term basis

• The existing storm water fund, general fund CIP and currently available federal funds will need to be supplemented

• We are researching innovative funding mechanisms nationally– Public or Public-Private partnerships– Special improvements tax districts

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Additional Next Steps• Brief City Council on results of the three focus

area studies and provide periodic briefings on status of city-wide coastal flooding study (January, 2011)

• Incorporate flooding vulnerability as part of the comprehensive plan update (ongoing, target date for completion is 2012)

• Work with HRPDC and Corps of Engineers to develop public information tools on coastal flooding for regional use (started discussions; will be ongoing)

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Conclusion• Norfolk recognizes that addressing flooding challenges is important

for the continued quality of life and economic vitality of our city and the region

• We are working to build upon our existing storm water program tofurther address our current flooding challenges and prepare for those of the future

• Norfolk has stepped forward in the region to engage local, regional, national and international experts and partners to assist us in fully analyzing the flooding issue and all of the potential mitigation options.

• The comprehensive long-term flood mitigation program currently under development will assist us in making the best strategic and cost effective use of resources to further enhance the livability of our coastal city.