2019 Spring NCBIWA Conference – Emerald Isle, NC
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Project Objectives: Two Interrelated Efforts • City of Elizabeth City Waterfront Master Plan • Assemble a long range, actionable plan for Elizabeth City’s +/- 1.2 miles of Downtown waterfront • Meaningfully engage the community in the plan making process, helping channel their voice and desires to reshape the waterfront • Ensure the plan accurately reflects current land use, economic and social conditions in Elizabeth City • Charles Creek Flooding Mitigation Plan • Assist the City with improvement efforts along Charles Creek designed to reduce / eliminate the long term risk to people and property caused by the continuing flooding issues experienced in that area • Explore the way Charles Creek and the overall waterfront can be more resilient to flooding events • Meet the requirements stipulated under the Local Planning and Management Grant by the Division of Coastal Management (CAMA) Sources: CIN, CLIA and LandDesign, 2016 - 5 -
KEY SURVEY RESULTS AND FINDINGS
Community Survey Effort • Three week survey effort to measure community preferences and gain insights on initial planning options • www.harborofhospitality.com • Survey effort ran from January 17 to February 9 • Tremendous feedback, with over 368 unique respondents and nearly 3,000 website views • Feedback was used to guide refined draft planning concepts • Complete survey results and comments available from the project website Sources: CIN, CLIA and LandDesign, 2016 - 7 -
Selected Survey Responses and Feedback Sources: CIN, CLIA and LandDesign, 2016 - 8 -
Selected Survey Responses and Feedback Sources: CIN, CLIA and LandDesign, 2016 - 9 -
WATERFRONT MASTER PLANNING CONCEPTS
Sources: CIN, CLIA and LandDesign, 2016 - 11 -
Sources: CIN, CLIA and LandDesign, 2016 - 12 -
Sources: CIN, CLIA and LandDesign, 2016 - 13 -
Sources: CIN, CLIA and LandDesign, 2016 - 14 -
Sources: CIN, CLIA and LandDesign, 2016 - 15 -
Sources: CIN, CLIA and LandDesign, 2016 - 16 -
Sources: CIN, CLIA and LandDesign, 2016 - 17 -
Sources: CIN, CLIA and LandDesign, 2016 - 18 -
Sources: CIN, CLIA and LandDesign, 2016 - 19 -
CHARLES CREEK FLOOD MITIGATION
Model Selection • XPSWMM 1D/2D selected due to low-lying ground elevations that allow wind tides to cause overland flow that also interacts with pipe networks Stormwater inlets __ Stormwater pipes __ Water level boundary condition 2D topographical surface color gradient (lower elevations in blue, higher elevations in orange) - 23 -
Model Setup – Tides/River Levels - 24 -
Model Setup – Tides/River Levels ___________________________________________________ 10 year surge elevation - 25 -
Model Results – 10 yr Rainfall with 1.0’ and 1.8’ Tides 10 yr, 1.8’ Surge 10 yr, 1.0’ Surge - 26 -
Model Results – 25 and 50 yr Rainfall with Corresponding Tides 50 yr, 3.6’ Surge 25 yr, 3.0’ Surge - 27 -
Potential Flood Mitigation Options Water Side of Berm Land Side of Berm • Protective berms • Flood gate and pumps Earthen Berm • Green infrastructure • Policy/ordinance revisions - 28 -
Potential Flood Mitigation Options - Berms • Protective berms along Charles Creek shoreline where needed to mitigate river and wind tide flooding • 25 yr return period storm selected (3 - 4.5’ NAVD) • ~7200 ft. of berm needed, 2 - 4 ft. high • Road raises needed where berms cross roadways (~1300 ft. of road, 2 – 4 ft. raise) • Conceptual level opinion of probable costs = $2 - $2.25M (berm and interior drainage) • Damages averted = $ 2.0M (taken from FIMAN website) - 29 -
Model Results - Berms Existing Conditions – 25 yr event With Berms – 25 yr event - 30 -
Potential Flood Mitigation Options – Flood Gate and Pumps • Flood gate immediately downstream of Riverside/Shepard St. Bridge • 50 yr return period storm selected (4 - 5’ NAVD) • 250’ ft. long gate structure, 25 – 100 cfs pumps – (24-36 in., 10k – 50k gpm) • Conceptual level opinion of probable costs = $6.0 – 8.5M • Damages mitigated = $6.0M (taken from FIMAN website) - 31 -
Model Results – Flood Gate and Pumps Existing Conditions – 50 yr event With Gate/Pump – 50 yr event - 32 -
Potential Flooding Mitigation Options – Green Infrastructure • Reduce impervious % to decrease runoff to stormwater infrastructure systems • Soil conditions are somewhat challenging • More of an add-on to other options to improve existing stormwater system behavior • Model results show that peak flows may be reduced by 5 - 10 % - 33 -
Funding Options and Approaches • FEMA Funding • Hazard Mitigation Grant Program • Pre-Disaster Mitigation Program • Flood Mitigation Assistance Program • HUD Community Development Block Grant Disaster Recovery • Clean Water Management Trust Fund Grants • NCDEQ Water Resources Development Grant Program • NOAA Coastal Resilience Grants Program • Clean Water State Revolving Fund - 34 -
Potential Flood Mitigation Options – Policy & Ordinance Revisions • Stormwater Ordinance • Update to reflect recent changes in stormwater rules, design guidance, and minimum criteria (DEQ, 2017) • Simplify design criteria storm events for consistency amongst land uses and development size • Encourage implementation of green infrastructure through language modification of Section G • Floods (Chapter 154 Code of Ordinances) • Add up to 1.5 feet of freeboard to FEMA flood elevations to provide additional safety and resilience - 35 -
Alternatives Analysis 25-yr storm event 50-yr storm event Flood Mitigation Option Probable Cost Probable Cost *berms do not provide full flood Protective Berms $2,200,000 $2,200,000 protection for 50-yr event Flood Gate and Pumps $7,000,000 $7,000,000 Property Buyout and Demolition $7,600,000 $10,100,000 Raise Buildings $1,600,000 $2,100,000 Move Buildings $3,500,000 $4,000,000 Approximate Flood Damages $2,000,000 $6,000,000 - 36 -
Recommendations • Elevating or relocating structures or protective berms are recommended flood mitigation alternatives • Protective berms can be used with greenway/walkway to improve connectivity between Elizabeth City universities • Green infrastructure can serve as an add-on to improve existing stormwater system behavior • Ordinance/policy revisions: • Update ordinance to reflect more 2017 stormwater rules and design guidance • Promote green infrastructure for water quantity and quality improvement with ordinance modifications • Provide additional freeboard on top of FEMA flood elevations - 37 -
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