Sea Level Rise/Recurrent Flooding in Virginia BeachAgriculture Advisory Commission October 9, 2017

1

Sea Level Rise Changes Flood Recurrence Intervals

Scenario Recurrence Intervals, yrToday 10 50 100 500

1.5 ft SLR 3 8 14 100

3 ft SLR 1 2 3 14

Theory

Observed – tidal Projected change in surge elevation recurrenceNOAA

Forbes

2

Sea Level Rise

3

VB SLR Planning Range

Annual Extreme Precipitation EventsNorfolk Airport Rain Gauge (NOAA/NWS)

4

Future Rainfall Strong evidence of already observed increases in heavy precipitation

occurrence and intensity at Norfolk and regionally Significant changes have occurred since 2000 Uncertainty is increasing about using the stationary assumption

Future precipitation-frequency curves increase most notably for 1-10 year events; ex: 2-year event increases by 30%

5

Flooding Issues: a Triple Threat

Rainfall Tidal

Backwater

WAVY.com

6

Stormwater Master Planning, Analysis, and Modeling Updating the City’s 31

Stormwater Drainage Area Models

Includes Preliminary Drainage Analysis to identify future Capital Drainage Projects

Models will allow Stormwater Engineering Center to provide starting tailwater elevations to developers for projects

Models will be live and reside in the Stormwater Engineering Center

7

STORMWATER MASTER PLANNING, ANALYSIS, ANDMODELING FIRST QUARTER ACTIVITIES

▪ Lynnhaven River Watershedo Watersheds 3, 5, & 8 are completeo Watersheds 7, 4, 30 & 6 to be completed by the end of the

year

▪ Southern Rivers Watershedo Watersheds 9 and 10 to be complete by the end of the yearo Watersheds 12-15 to be complete by February 2019o Watersheds 11, 16, 23-28 to be complete by April 2020o Alternative Models better suited to modeling basins with

extremely flat topographic relief being considered for the lower Southern Watershed

8

Comprehensive Sea level Rise Study Three Phases

9

Project Status

• Phase 1 – Impact Assessment: Recently completed for all four major watersheds in Virginia Beach

• Phase 2 – Adaptation Strategies:• Lynnhaven: Underway, 2018 Spring • Southern Watershed: Underway, 2018 Summer• Elizabeth River: 2017 Fall to 2018 Summer• Beach Borough: 2017 Winter to 2018 Fall

• Public Engagement• 2017 fall to 2018 Fall

10

Flood Extent Changes

11

Change in Flood Area

12

Total Annualized Losses

Watershed

Total Building InventoryBillions Today 1.5 ft SLR 3 ft SLR

Estimated Value % of Total Combined

Loss Loss Ratio Combined Loss Loss Ratio Combined

Loss Loss Ratio

Elizabeth River $10.3 13% $2.70 0.03% $8.57 0.08% $24.25 0.24%Lynnhaven $42.7 53% $17.29 0.04% $55.94 0.13% $164.08 0.38%Southern $24.5 30% $5.14 0.02% $19.58 0.08% $170.84 0.70%Oceanfront $3.6 4% $0.55 0.02% $2.50 0.07% $16.20 0.44%

City-wide $81.1 100% $25.69 0.03% $86.58 0.11% $375.37 0.46%

• Structural, Content, Business Disruption LossesLosses, Millions

$0$50

$100$150$200$250$300$350$400

Today 1.5 ft SLR 3 ft SLR

Loss

es, M

illion

s

13

Watershed Loss Changes with SLRWatershed Today 1.5 SLR 3 ft SLR

Elizabeth River 2.48 8.18 23.60

Lynnhaven 15.97 53.27 158.14

Southern 4.62 17.94 165.31

Oceanfront 0.49 2.37 15.72

Total: 23.56 81.76 362.77

Annualized Losses, Millions

14

Annualized Loss Concentration – Today

15

Annualized Loss Concentration – 1.5 ft SLR

16

Annualized Loss Concentration – 3 ft SLR

5

4

1

3

17

Relative Concentration of LossesScenario = 3 ft SLRTotal Annualized Building and Contents Losses

Loss Category

18

Preliminary Assessment of Great Bridge Lock

Southern VB to near Cape Lookout, NCCaptures full potential fetch across Pamlico, Albemarle, and Currituck SoundsOpen boundary on S. branch of Elizabeth River

19

Model Setup & Conclusion• Grid

• Source: FEMA Region III Flood Insurance Study• Modifications:

• Ran model with the canal/locks open• Created 2nd version with canal/locks closed by implementing

wall at 15 ft NAVD88 across full width of canal• Compared results

• Wind forcing - constant wind from due south at 15 mph (6.7 m/s)

• Locks had minimal effect on wind tide elevations along the North Landing River

• Locks had no effect on wind tide elevations in Back Bay

20

Wind-tide and Flooding Investigations • The City has offered to cost participate with the USACOE in

a study of the effect of the Great Bridge Locks. In light of the Dewberry assessment, this may not be a wise use of funds

• Dewberry is working on an assessment of wind tides. That work is expected by Summer 2018

• Public Works is looking at the feasibility to elevate some roads

• Indian River Road (between West Neck and PA (2 miles)• Sandbridge Road (between Flanagans and Colechester including

the New Bridge intersection, (0.7 miles)• Pungo Ferry Road (Blackwater Road to the bridge) (2 miles)

21

2017 2018Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4

Impact AssessmentHazard Analysis and MappingBuilding Risk AssessmentWater Resources AnalysisInfrastructure Vulnerability

Strategy Development, Evaluation, Plan Formulation

Lynnhaven Development Evaluation Plan

Southern

Elizabeth River

Oceanfront

Outreach

Public Engagement General Information Strategy Discussion Plan Outreach

If additional time needed for coordination, etc.

Schedule

22

Coordination/Outreach• Conducted City Manager and City Council briefings in July• Prepared draft Public Engagement Plan• Southern Watershed Stormwater Meeting conducted on

August 2, 2017• Working to finalize coordination of responsibilities and

develop initial timeline of fall activities• Public meetings (3-4) to be conducted by ODU/VA Sea

Grant this fall - scheduling underway

23

Questions?

24