Topics

o Sea Level Rise and the Southern Watersheds

o Ashville Park

o Sherwood Lakes

o Kingston Estates

o Drainage Operations & Maintenance in the Southern Watersheds

PRINCESS ANNE DISTRICT STORMWATER PROJECTS

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SEA LEVEL RISE AND THE SOUTHERN WATERSHEDS

DR. BRIAN BATTEN, DEWBERRY

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Flood Complaints

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City Response to Issues

• Virginia Beach City Council provided funding for a comprehensive sea level rise and recurrent flooding assessment and response plan in FY15

• Dewberry, a national consultant firm, retained by the City to conduct study in January 2015

• City awarded $850k grant from NOAA in March 2016• Collaborative effort with Stormwater Master Plan

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Study Goal and OutcomesGoal: Produce information and strategies that will enable Virginia Beach to establish long-term resilience to sea level rise and associated recurrent flooding

Outcomes:

• A full understanding of flood risk and anticipated changes over planning and infrastructure time horizons

• Actionable flood resilience plans that combine engineered protection measures, accommodation, and/or land use management strategies

• A fine-tuned public outreach process to advance resilience initiatives

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Watershed Level Plans• Economic and environmental diversity require 4 distinct

plans

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Comprehensive SLR Study Approach

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Phase 1: Sea Level Rise/Recurrent Flooding Impacts

• Objective: Identify the location, frequency and potential cost of existing and future flood risk to the City

• How will vulnerability change with increasing flood levels due to SLR?

• Where will we see the flood footprint expand?

• How much more frequent will flooding occur?

• What assets are vulnerable?• What are the losses, how will they

change? • What assets are at the highest risk?

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SLR and Recurrent Flooding

Today’s 1-yr water levelwas the 10-yr water level in the 1950s

Image Credit: NOAA

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SLR Observations

Local/Regional Trends

Rise in Last 50-yearsLocation Increase, ft

Sewells Point 0.8Chesapeake Bay

Bridge Tunnel 1

Duck 0.7Oregon Inlet 0.7

Norfolk

Chesapeake Bay

Duck, NC

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VB SLR Planning Scenarios

Life Cycle Alignment

Time Horizon/

Time Period

SLR Value Relevance Use

Municipal Planning

20-40 years2035-2055 1.5 ft

Comprehensive Plan & Outcomes

Short end of Commercial and Utility

life-cycles

Vulnerability assessmentKey planning value

Basis for evaluation of all adaptation strategies

Critical Infrastructure

Long-term awareness

AdaptiveCapacity

50-70 years

2065-20853.0 ft

Utility Infrastructure life-cycle

Transportation infrastructure

lifecyclesResidential structure

lifecycles

Secondary vulnerability assessment to provide insight into

long-term risk Basis for long-term infrastructure

decisionsEvaluate cost-effectiveness of

additional protection for adaptable resilience strategies

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Flood Assessment Conditions• Tidal

• Daily tidal flooding• Future permanent inundation• Defined by NOAA, Mean Higher High Water

• Nuisance • Wind-driven surge, extreme tide events• Repetitive losses/

loss of function or service• Defined by water level analysis

• Storm Surge• Nor’easters, tropical storms, hurricanes• 10-, 25-, 50-, 100-, 500-yr recurrence intervals• Defined by probabilistic analysis

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Southern Watershed Issues – Wind Tides• Southerly winds push

water into Back Bay, North Landing River

• Flood low-lying areas

• Instances since early 1900’s

• Ongoing area of focus• Design water surface

elevations in the Virginia Beach Public Works Standards and Specifications exceeds wind tide levels

Credit: SeaGrant

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Flood elevations - Not a static increase!• SLR Integration:

• 1.5 ft SLR scenario • Added as a static increase to surge elevations• Non-linear aspects captured through re-evaluation of dune erosion and

wave modeling over increased water levels.• 3 ft SLR scenario

• Detailed modeling from USACE and North Carolina used to integrate non-linear response in surge elevations

• Wave modeling and dune erosion also re-evaluated.

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Projected Changes in Coastal FloodingCity-wide, areas subject to flooding will increase:• In 30-40 years: 1.5 times• In 60-70 years: 2 times

Changes in the Southern watershed represent 70-80% of the city-wide total

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Changes in Flood Risk –Southern Watershed

• Flood losses increase due to deeper, more frequent flooding

• 3-4 times increase in next 30-yrs

Watershed Today 1.5 SLR 3 ft SLR

Southern 4.62 17.94 165.31

City Total: 23.56 81.76 362.77

Annualized Losses, Millions

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Public Engagement • Capturing Perceptions, Increasing Issue Awareness

Fall 2017• Interactive public sessions to solicit public opinions and perceptions on flood

issues and priorities• Series of public presentations to acquaint public with study process, initial

results, path forward

• Solution PerspectivesSpring 2018• Initial presentation and gathering of public feedback on flood management

strategies

• Plan AwarenessSummer/Fall 2018• Public presentation of final plans and strategy approaches/timelines

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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 Study Introduction, Engagement

Strategy Discussion Plan Outreach

If additional time needed for coordination, etc.

Schedule

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ASHVILLE PARKCJ BODNAR, P.E., PW-ENGINEERING

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ASHVILLE PARK ENGINEERING ANALYSIS• CDM Smith performed hydraulic analyses of the Ashville

Park stormwater system and developed solution alternatives.

• Model of stormwater system was developed using EPA Storm Water Management Model (SWMM).

• EPA SWMM is a complex mathematical model in widespread use across the country (gold standard).

• Nine months to complete, $218,000 to date

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ASHVILLE PARK MODEL CALIBRATION• Photos and information from the neighborhood helped

provide guidance and after-the-fact water elevation data

• Public Works installed three water surface level gauges for data

• SWMM Model was calibrated using Tropical Storm Julia & Hurricane Matthew

• The model predicted flood water elevations that were within an inch of actual elevations for both storms

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ASHVILLE PARK MODEL CALIBRATION

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Outfall The outfall system to Flanagan’s Lane and Sandbridge Road is

inadequate. The rock weir cannot pass nearly enough water during a storm to keep the stormwater within the banks of the lakes

STUDY FINDINGS

The receiving ditches and channels downstream of the outfall do not have capacity to handle the stormwater, resulting in higher water elevations

When water levels are high in Back Bay and Ashville Bridge Creek, even less water can pass the outfall

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STUDY FINDINGS (CONTINUED)

Subdivision Lakes & Stormwater Piping▪ The stormwater piping and the lakes are inadequate

▪ There is not sufficient lake area to store runoff until it can drain through the system

▪ Higher water levels in the lakes prevent the stormwater pipes in the streets from draining quickly during and after storms

▪ Even with lowered lake elevations and more lake area, the pipe system cannot carry enough stormwater to keep the streets from flooding during significant events

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ALTERNATIVES EVALUATED▪ CDM Smith evaluated over 25 improvement scenarios and

provided detailed analyses of the four most viable alternatives▪ All 4 alternatives provide similar benefits; however, no

improvement can provide complete protection from all storm events (much greater than 100-year event)

▪ All 4 alternatives require major improvements & upgrades to the neighborhood drainage system (within the streets)

▪ Alternative D is more resilient to future water levels because of the location of the proposed pump station

▪ Alternative B is more conducive to phasing and its initial phases can be implemented faster than the initial phases of Alternative D

▪ In addition to flood reduction, all alternatives provide additional stormwater quality treatment through expanded and new BMPs (wet ponds)

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ASHVILLE PARK – ALTERNATIVE B

Hard Cost – $23.5M (does not include acquisition, utility adjustments or environmental mitigation costs)

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ASHVILLE PARK – ALTERNATIVE D

Hard Cost – $21.2M (does not include acquisition, utility adjustments or environmental mitigation costs)

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INTERIM IMPROVEMENTS – PHASED APPROACH

▪ The FY2018-23 CIP provides $9 million in funding which will allow for the first phase of Alternative B (a.k.a Scenario 5)o Considerable decrease in flooding duration

o Incremental improvement in the depth of flooding

o Planning level opinion of cost is $8.2 million

▪ The neighborhood and the developer both indicate a desire to continue with the development as long as there are no adverse impacts to the stormwater system in the existing villages

▪ Public Works Engineering has begun the preliminary engineering design of the Scenario 5 improvements

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SCENARIO 5 IMPROVEMENTS

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POSSIBLE VILLAGE C COST-PARTICIPATION▪ Scenario 5 improvements assume Village C will be developed

▪ HomeFed is interested in proceeding with Village C and cost-participating in Scenario 5

▪ Cost-participation based upon additional cost of the phased approach

▪ Cost share is $5.8M (71%) City, $2.4M (29%) HomeFed for initial phase (Alt. B, Scenario 5)

▪ HomeFed to cost participate up to $2.1M in future phases if Villages D & E proceed

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ASHVILLE PARK INTERIM PROJECTS▪ Dedicated 13 CFS portable pump to lower the 15-lake system

prior to significant storm events (3” rain or greater)

▪ New weir and portable pump site will be constructed at existing outfall location to allow more discharge from the lake system and also prevent high water backflow into the system

▪ Weir construction scheduled for January 2018

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ASHVILLE PARK INTERIM PROJECT

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SHERWOOD LAKESMIKE MUNDY, P.E., PW-ENGINEERING

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Lake Drainage Area (DA) 364 ac

Lake Surface Area (SA) 123 ac

Sherwood Lakes Sherwood Lakes

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Temporary Pumping North Lake

Sherwood Lakes

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Sherwood Lakes 1. Pump Station (5 CFS) with additional connection for temporary pump and generator

2. Intake pipe for pump station

3. Discharge Pipe from pump station

4. New storm sewer pipe (to provide some interconnection between the two ponds)

Permanent Pump Station Locations

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KINGSTON ESTATES(PREVIOUSLY KNOWN AS KING’S LANDING)

LOCATED ON WEST NECK ROAD

NANCY MCINTYRE, P.E., L.S., DEVELOPMENT SERVICES ADMINISTRATOR

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KINGSTON ESTATES

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KINGSTON ESTATES

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DRAINAGE OPERATIONS & MAINTENANCE IN THE SOUTHERN WATERSHEDS

MARK JOHNSON, P.E., OPERATIONS ENGINEER

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CIP PROJECTS

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CIP PROJECTSMap ID Project Description Project Location PhaseStormwater Infrastructure Rehabilitation & Improvements, CIP 7-416

19 Ashville Park Weir 1471 Flanagans Lane Design25 Land of Promise Ditch Unit ID S8023, S8016 On Hold

27 Mill Landing Road/Halstead Shore Stabilization

1301 Mill Landing Road, 1218 Mill Landing Road Design

29 Municipal Center Drainage Infrastructure Survey Municipal Center Surveying

31 Princess Anne Road Enterprise Intersection of Princess Anne & Nimmo Parkway Construction

38 Dam Neck Road Pipe Rehabilitation Phase II

Dam Neck Road, London Bridge Road, Harpers Road Design

41 Community Canal Unit ID 23160-008D StudyPrimary System Infrastructure Improvements, CIP 7-023

45 Mill Landing/Nanney Creek 1852 Mill Landing Road Permitting48 Off-Road Ditch Program Zone E, K, L, & N Ditches On-Going

Stormwater Pump Station Modifications, CIP 7-41276 Sherwood Lakes Intake Design

Southern Canal / Lead Ditch and Culvert Improvements, CIP 7-024Charity Neck Road 3801 Charity Neck Road ScopingPleasant Ridge Road 1600 Pleasant Ridge Road Scoping

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OFF ROAD DITCH PROGRAM Ditch Cleaning Cycles: 16 years - Original Cycle

8 years - Goal Cycle

12 years - Current Cycle

Other FY 18 Projects: Canal #2 Inspect/Repair -

$300K

Salem Canal Inspect/Repair - $250K

West Neck Creek Inspect/Repair - $350K

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STORMWATER MAINTENANCE AND INSPECTIONS▪ Currently 124 open work orders in the Princess Anne

District▪ Roadside Ditch: 11▪ Cave-in: 81▪ Pipe Cleaning: 32

▪ Street Sweeping - All City roads are swept 6 times per year (once every other month)

▪ MS4 Inspections▪ Asset Inspections - 15% of known assets (pipes, structures,

ditches) shall be inspected annually▪ SWMF Inspections – all City maintained SWMF inspected

annually, and 20% of the privately maintained SWMF inspected annually.

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END OF PRESENTATIONPROCEED TO INFORMATION STATIONS

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