informational meeting stormwater design requirements · 04/12/2017 · 3500 dam neck road ....
TRANSCRIPT
Consultants, Builders and Developers Informational Meeting
Stormwater Design Requirements
Monday, December 4, 20179:00 AM – 11:00 AM
Public Utilities Operations Multipurpose Rooms3500 Dam Neck Road
Virginia Beach, VA 23453
December 5, 2017 Consultants, Builders and Developers Meeting 2
MEETING AGENDA
1. Welcome, Introduction of Speakers and Facilitator, Meeting Agenda – J. Barry Frankenfield, Director
2. Introduction of the Public Works Stormwater Engineering Center – Toni Alger, P.E., SWEC Administrator
3. Public Works Stormwater and Sea Level Rise Update – C. J. Bodnar, P.E. and Greg Johnson, P.E.
4. Preliminary Stormwater Analysis; Projects needing City Council Approval – Seth Edwards, P.E., DSC Engineering Supervisor
5. FINAL Stormwater Engineering Submittal/Review – Seth Edwards, P.E., DSC Engineering Supervisor
6. Final Stormwater DESIGN COMPONENTS – Seth Edwards, P.E., DSC Engineering Supervisor
7. Questions and Answers, Comments and Suggestions Session – Bob Trahan, Facilitator, STIR Office
8. Closing Remarks - J. Barry Frankenfield, Director
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Stormwater Engineering Center
December 4, 2017
Toni Alger, P.E.C.J. Bodnar, P.E.Greg Johnson, P.E.
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Areas of Known Flooding
• Windsor Woods• Shore Drive• The Lakes• Sherwood Lakes• Princess Ann Plaza• Northgate• Ashville Park • Central Resort Area
• College Park• Level Green• Oceana Village• Lamplight Manor• Green Run• Lake Chubb/Bradford• Aragona
The City has a long and likely growing list of areas of known flooding. Public and private projects in those areas will have to consider the existing and future conditions.
Many are attributable to rising sea levels and increasing rainfalls.
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Stormwater Master Planning
Current Master Plans date from the late 1980s to early 1990s
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Stormwater Master Plan – Why update?• Update stormwater system inventory• Create computer models of the
current stormwater system utilizing readily available software
• Assess performance of stormwater system– Flood control– Stormwater quality
• Identify deficiencies in the stormwater system
• Determine needed improvements• Provide information for project
designs• Create Comprehensive Stormwater
Management Plans where possible
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Comparison of Previous to Current
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GIS Mapping
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Comprehensive Master Plan Integration of multiple stormwater issues
• Stormwater management and flood mitigation
• 31 Watersheds • Stormwater quality
– TMDLs (TN, TP, TSS, bacteria)
• Regulatory compliance– NPDES MS4, TMDLs– System Inventory
• Sea level rise and tidal surge
• Capital improvement planning and funding
• Design Information for Projects
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Hydrologic & Hydraulic Parameters• Impervious cover
• Soil type / Land use
• Depth to groundwater
• Rainfall depth and distribution
• Boundary conditions
• Catchment geometry
• Inventory of System characteristics
• Boundary Conditions (tailwater)
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Sea Level Rise• City is developing a
Comprehensive Response Plan to Sea Level Rise
• City’s Plan is utilizing projected increases in sea level per the VIMS 2013 report to the General Assembly
• Among its many impacts, sea level rise will obviously impact drainage system performance in many, if not most areas of the City.
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3 ft1.5 ft
Evaluate for Adaptive Capacity
Action
Selected Scenarios vs Federal Curves
Life Cycle Alignment Time Horizon/Time Period SLR Value Relevance Use
Municipal Planning 20-40 years
2035-20551.5 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
50-70 years
2065-2085
3.0 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
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Projected Changes in Coastal Flooding
• Areas subject to flooding will increase:
• In 30-40 years: 1.5 times present area
• In 60-70 years: 2 times present area
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Combined Impact on Stormwater Analysis• Higher coastal water levels diminish stormwater system performance
• Stormwater Conveyance
• Combined Flooding
• Coastal Flooding
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Changes in Rainfall• Regional Precipitation Trends
• Heavy rainfall increasing
• Future precipitation conditions• Up to 20% increase in design rain
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Pending Updates to City Stormwater Standards
• Clarify and Consolidate in one place – easier to understand and locate
• Incorporating changes in rainfall intensities
• Adapting to sea level rise-ongoing work
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Creating Comprehensive Stormwater Management Plans“Comprehensive stormwater management plan” means a plan, whichmay be integrated with other land use plans or regulations, that specifieshow the water quality components, quantity components, or both ofstormwater are to be managed on the basis of an entire watershed or aportion thereof. The plan may also provide the remediation of erosion,flooding, and water quality and quantity problems caused by priordevelopment. – VAC Chapter 60
Must be approved by DEQ
• Allows stormwater control measures on a watershed basis• Potential to reduce specific VSMP on-site requirements for public and
private project in an area covered by a comprehensive stormwater management plan (CSWMP)
• Individual project will still need to demonstrate that the project’s stormwater design work in the context of the CSWMP and that other requirement of VSMP and proper drainage are satisfied.
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DEQ Energy Balance Equation/CSMP
.....Reviewing the submittal as a CSMP, DEQ recognizes the use of SWMM is a valid tool to demonstrate channel and flood protection in accordance with the objectives of the VSMP regulations….
The City’s model appears to be a holistic hydraulic approach that integrates increase discharges from an individual project into the Cities stormwater network during wet weather flows and during tidal fluctuations.
The City’s model integrates the incremental difference between pre and post- developmental flows that enter into the stormwater network system during storm events, i.e. wet weather conditions.
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Important References
“The Designer must recognize that individual site development plans or a retrofits of drainage facilities in urban areas may be only a part of a larger system and that he must integrate his design into a larger system , particularly with respect to creating upstream and downstream hazards.”
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Final Thought - Plan to fail“Somehow we have to find the middle ground between dangerous rigidity and catastrophic collapse. In our organizations, social and political systems, and individual lives, we need to create the possibility for what computer programmers and disaster planners call “graceful” failure.When a system fails gracefully, damage is limited, and options for recovery are preserved. Also, the part of the system that has been damaged recovers by drawing resources and information from undamaged parts.”
Thomas Homer-Dixon
The Upside of Down
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In Summary….. Credits to Yogi Berra
“You can observe a lot by watching.”“If you don’t know where you are going, you might wind up someplace else.”“It’s deja vu all over again.”“It ain’t over till it’s over.”
December 5, 2017 Consultants, Builders and Developers Meeting 22
Planning and Community Development/Development Services CenterStormwater Review
Preliminary Stormwater Engineering Analysis FAQs(Handout page 2)
1. When is this needed? 2. Why is it needed?3. What information is needed? 4. Is this required or just recommended?5. What is the Submittal/Review Process? 6. Why are two engineering teams reviewing the preliminary analysis?
December 5, 2017 Consultants, Builders and Developers Meeting 23
FINAL Stormwater Management Plan Submittal and Review FAQs(Handout page 5)
1. When is a Stormwater Management Plan required?2. When is an Erosion & Sediment Control Plan and MS 19 compliance (downstream capacity and
erosion) required?3. Who reviews the stormwater management plan and supporting calculations, reports, maps,
etc.? 4. Who has the existing drainage system and watershed information needed for design?5. What does each Department review?6. How long does the review take?7. Who do I contact if I disagree with the stormwater comments, have questions, or want to
meet?8. Who approves the final stormwater management plan?9. When is a Stormwater Management Facilities Maintenance Agreement (SWMA) required?
December 5, 2017 Consultants, Builders and Developers Meeting 24
Final Stormwater DESIGN COMPONENTS(Handout page 7)
• Erosion and Sediment Control - Minimum Standard 19
• Minimum Technical Criteria:
Grandfathered (IIC Design Criteria) Non Grandfathered (IIB Design Criteria)
• City Design Requirements for All Projects
December 5, 2017 Consultants, Builders and Developers Meeting 25
Erosion and Sediment Control - Minimum Standard 19(from 9VAC25-840)(Handout page 7)
19. Properties and waterways downstream from development sites shall be protected from sediment deposition, erosion and damage due to increases in volume, velocity and peak flow rate of stormwater runoff for the stated frequency storm of 24-hour duration in accordance with the following standards and criteria. Stream restoration and relocation projects that incorporate natural channel design concepts are not man-made channels and shall be exempt from any flow rate capacity and velocity requirements for natural or man-made channels
December 5, 2017 Consultants, Builders and Developers Meeting 26
Stormwater Management Ordinance - City Code, Appendix D(Handout page 9)
“Grandfathered” Projects
May use Part II C technical criteria (may also use Part IIB technical critieria)
Water Quality -Performance Based Criteria (old calculation forms - 4 “situations”)
Water Quantity – stream channel erosion and flooding
December 5, 2017 Consultants, Builders and Developers Meeting 27
NON- “Grandfathered” Projects (Handout page 10)
• Any project not meeting the “grandfathering” conditions must use Part II B technical criteria
Water Quality – VRRM spreadsheet
Water Quantity - Channel Protection
Water Quantity - Flood Protection
December 5, 2017 Consultants, Builders and Developers Meeting 28
City Design Requirements/Considerations for all Projects(Handout page 12)
Tailwater
Design methods
100-year 24-hour storm event
Site Conditions Input Data
Various other local design requirements
What is included in a typical SW Design submittal?
December 5, 2017 Consultants, Builders and Developers Meeting 29
Experiences and Suggestions
We are listening to you!