2019 Spring NCBIWA Conference Emerald Isle, NC - 2 - - 3 - - 4 - - - PowerPoint PPT Presentation

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

KEY SURVEY RESULTS AND FINDINGS

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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

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Sources: CIN, CLIA and LandDesign, 2016

Selected Survey Responses and Feedback

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Sources: CIN, CLIA and LandDesign, 2016

Selected Survey Responses and Feedback

WATERFRONT MASTER PLANNING CONCEPTS

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Sources: CIN, CLIA and LandDesign, 2016

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Sources: CIN, CLIA and LandDesign, 2016

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Sources: CIN, CLIA and LandDesign, 2016

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Sources: CIN, CLIA and LandDesign, 2016

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Sources: CIN, CLIA and LandDesign, 2016

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Sources: CIN, CLIA and LandDesign, 2016

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Sources: CIN, CLIA and LandDesign, 2016

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Sources: CIN, CLIA and LandDesign, 2016

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Sources: CIN, CLIA and LandDesign, 2016

CHARLES CREEK FLOOD MITIGATION

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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

• range)

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Model Setup – Tides/River Levels

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Model Setup – Tides/River Levels

___________________________________________________ 10 year surge elevation

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Model Results – 10 yr Rainfall with 1.0’ and 1.8’ Tides

10 yr, 1.0’ Surge 10 yr, 1.8’ Surge

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Model Results – 25 and 50 yr Rainfall with Corresponding Tides

25 yr, 3.0’ Surge 50 yr, 3.6’ Surge

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Potential Flood Mitigation Options

• Protective berms
• Flood gate and pumps
• Green infrastructure
• Policy/ordinance revisions

Water Side of Berm Land Side of Berm

Earthen Berm

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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)

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Model Results - Berms

Existing Conditions – 25 yr event With Berms – 25 yr event

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Potential Flood Mitigation Options – Flood Gate and Pumps

• Flood gate immediately downstream
• f 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)

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Model Results – Flood Gate and Pumps

Existing Conditions – 50 yr event With Gate/Pump – 50 yr event

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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
• ptions to improve existing

stormwater system behavior

• Model results show that

peak flows may be reduced by 5 - 10 %

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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

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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

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Alternatives Analysis

Flood Mitigation Option Probable Cost Probable Cost Protective Berms $2,200,000 $2,200,000 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

25-yr storm event 50-yr storm event

*berms do not provide full flood protection for 50-yr event

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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
• rdinance modifications
• Provide additional freeboard on top of FEMA flood elevations