PRINCESS ANNE DISTRICT STORMWATER PROJECTS

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George Curtis
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Ashville Park Sherwood Lakes Kingston Estates

1 PRINCESS ANNE DISTRICT STORMWATER PROJECTS Topics o o o o o Sea Level Rise and the Southern Watersheds Ashville Park Sherwood Lakes Kingston Estates Drainage Operations & Maintenance in the Southern Watersheds 1

2 SEA LEVEL RISE AND THE SOUTHERN WATERSHEDS DR. BRIAN BATTEN, DEWBERRY 2

3 3 Flood Complaints

4 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 4

5 Study Goal and Outcomes Goal: 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, and/or floodplain management strategies A fine-tuned public outreach process to advance resilience initiatives 5

6 Watershed Level Plans Economic and environmental diversity require 4 distinct plans 6

7 7 Comprehensive SLR Study Approach

Phase 1: Sea Level Rise/Recurrent Flooding Impacts Objective: Identify

risk to the City How will vulnerability change with increasing flood

How much more frequent will flooding occur? What assets are vulnerable?

8 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? 8

9 SLR Observations Local/Regional Trends Norfolk 9 Chesapeake Bay Duck, NC Rise in Last 50-years Location Increase, ft Sewells Point 0.8 Chesapeake Bay Bridge Tunnel 1 Duck 0.7 Oregon Inlet 0.7

10 SLR and Recurrent Flooding Image Credit: NOAA 10 Today s 1-yr water level was the 10-yr water level in the 1950s

11 VB SLR Planning Scenarios Life Cycle Alignment Time Horizon/ Time Period SLR Value Relevance Use Municipal Planning years ft Comprehensive Plan & Outcomes Short end of Commercial and Utility life-cycles Vulnerability assessment Key planning value Basis for evaluation of all adaptation strategies Critical Infrastructure Long-term awareness Adaptive Capacity years ft Utility Infrastructure life-cycle Transportation infrastructure lifecycles Residential structure lifecycles Secondary vulnerability assessment to provide insight into long-term risk Basis for long-term infrastructure decisions Evaluate cost-effectiveness of additional protection for adaptable resilience strategies 11

12 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 12 Storm Surge Nor easters, tropical storms, hurricanes 10-, 25-, 50-, 100-, 500-yr recurrence intervals Defined by probabilistic analysis

Southern Watershed Issues Wind Tides Southerly

Flood low-lying areas Instances since early 1900 s

elevations in the Virginia Beach Public Works

13 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 13

re-evaluation of dune erosion and wave modeling over increased water levels.

14 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 nonlinear response in surge elevations Wave modeling and dune erosion also re-evaluated. 14

Projected Changes in Coastal Flooding City-wide, areas subject to flooding will increase: In 30-40 years: 1.

15 Projected Changes in Coastal Flooding City-wide, areas subject to flooding will increase: In years: 1.5 times In years: 2 times Changes in the Southern watershed represent 70-80% of the city-wide total 17

16 Changes in Flood Risk Southern Watershed Flood losses increase due to deeper, more frequent flooding 3-4 times increase in next 30-yrs Annualized Losses, Millions Watershed Today 1.5 SLR 3 ft SLR Southern City Total:

17 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 Perspectives Spring 2018 Initial presentation and gathering of public feedback on flood management strategies Plan Awareness Summer/Fall 2018 Public presentation of final plans and strategy approaches/timelines 17

18 Schedule Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Impact Assessment Hazard Analysis and Mapping Building Risk Assessment Water Resources Analysis Infrastructure Vulnerability Strategy Development, Evaluation, Plan Formulation Lynnhaven Development Evaluation Plan Southern Elizabeth River Oceanfront Outreach Public Engagement Study Introduction, Engagement Strategy Discussion Plan Outreach 18 If additional time needed for coordination, etc.

19 ASHVILLE PARK CJ BODNAR, P.E., PW-ENGINEERING 19

20 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 20

21 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 21

22 ASHVILLE PARK MODEL CALIBRATION 22

23 STUDY FINDINGS 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 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 23

24 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 24

25 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) 25

26 ASHVILLE PARK ALTERNATIVE B Hard Cost $23.5M (does not include acquisition, utility adjustments or environmental mitigation costs) 26

27 ASHVILLE PARK ALTERNATIVE D Hard Cost $21.2M (does not include acquisition, utility adjustments or environmental mitigation costs) 27

28 INTERIM IMPROVEMENTS PHASED APPROACH The FY 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 28

29 SCENARIO 5 IMPROVEMENTS 29

30 POSSIBLE VILLAGE C COST-PARTICIPATION Scenario 5 improvements assume Village C will be developed HomeFed is interested in proceeding with Village C and costparticipating 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 30

31 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

32 ASHVILLE PARK INTERIM PROJECT 32

33 SHERWOOD LAKES MIKE MUNDY, P.E., PW-ENGINEERING 33

34 Sherwood Lakes Sherwood Lakes Lake Drainage Area (DA) 364 ac Lake Surface Area (SA) 123 ac 34

35 Sherwood Lakes Temporary Pumping North Lake 35

36 Sherwood Lakes 1. Pump Station (5 CFS) with additional connection for temporary pump and generator Permanent Pump Station Locations 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) 36

37 KINGSTON ESTATES (PREVIOUSLY KNOWN AS KING S LANDING) LOCATED ON WEST NECK ROAD NANCY MCINTYRE, P.E., L.S., DEVELOPMENT SERVICES ADMINISTRATOR 37

38 KINGSTON ESTATES 38

39 KINGSTON ESTATES 39

40 DRAINAGE OPERATIONS & MAINTENANCE IN THE SOUTHERN WATERSHEDS MARK JOHNSON, P.E., OPERATIONS ENGINEER 40

41 CIP PROJECTS 41

42 CIP PROJECTS Map ID Project Description Project Location Phase Stormwater Infrastructure Rehabilitation & Improvements, CIP Ashville Park Weir 1471 Flanagans Lane Design 25 Land of Promise Ditch Unit ID S8023, S8016 On Hold 27 Mill Landing Road/Halstead Shore 1301 Mill Landing Road, 1218 Mill Landing Stabilization 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 Dam Neck Road, London Bridge Road, Harpers II Road Design 41 Community Canal Unit ID D Study Primary System Infrastructure Improvements, CIP Mill Landing/Nanney Creek 1852 Mill Landing Road Permitting 48 Off-Road Ditch Program Zone E, K, L, & N Ditches On-Going Stormwater Pump Station Modifications, CIP Sherwood Lakes Intake Design Southern Canal / Lead Ditch and Culvert Improvements, CIP Charity Neck Road 3801 Charity Neck Road Scoping Pleasant Ridge Road 1600 Pleasant Ridge Road Scoping 42

43 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 43

44 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. 44

45 END OF PRESENTATION PROCEED TO INFORMATION STATIONS 45

ASHVILLE PARK STORMWATER UPDATE

ASHVILLE PARK STORMWATER UPDATE JULY 18, 2017 1 ASHVILLE PARK CHRONOLOGY 2005: Ashville Park conditionally rezoned. Consisted of Five Villages 2006-2007: Village A Wilshire Village was approved and construction