Consultants, Builders and Developers Informational Meeting Stormwater Design Requirements

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Gavin Whitehead
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4, 2017 9:00 AM 11:00 AM Public Utilities Operations

1 Consultants, Builders and Developers Informational Meeting Stormwater Design Requirements Monday, December 4, :00 AM 11:00 AM Public Utilities Operations Multipurpose Rooms 3500 Dam Neck Road Virginia Beach, VA 23453

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 December 5, 2017 Consultants, Builders and Developers Meeting 2

3 Stormwater Engineering Center December 4, 2017 Toni Alger, P.E. C.J. Bodnar, P.E. Greg Johnson, P.E. 3 Stormwater Design December 4, 2017

4 Areas of Known Flooding 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. 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 4 Stormwater Design December 4, 2017

5 Stormwater Master Planning Current Master Plans date from the late 1980s to early 1990s 5 5 Stormwater Design December 4, 2017

6 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 6 Stormwater Design December 4, 2017

7 7 Stormwater Design December 4, 2017 Comparison of Previous to Current

8 GIS Mapping 8 Stormwater Design December 4, 2017

Comprehensive Master Plan Integration of multiple stormwater issues Stormwater management and flood mitigation 31 Watersheds Stormwater quality TMDLs (TN, TP, TSS, bacteria) Regulatory

9 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 9 Stormwater Design December 4, 2017

10 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) 10 Stormwater Design December 4, 2017

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

11 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 Stormwater Design December 4, 2017

12 Selected Scenarios vs Federal Curves Evaluate for Adaptive Capacity Action 3 ft 1.5 ft Life Cycle Alignment Municipal Planning Critical Infrastructure Long-term awareness Adaptive Capacity Time Horizon/ Time Period years years SLR Value Relevance Use 1.5 ft 3.0 ft Comprehensive Plan & Outcomes Short end of Commercial and Utility life-cycles Utility Infrastructure lifecycle Transportation infrastructure lifecycles Residential structure lifecycles Vulnerability assessment Key planning value Basis for evaluation of all adaptation strategies 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 12 Stormwater Design December 4, 2017

Projected Changes in Coastal Flooding Areas subject to flooding will increase: In 30-40 years:

13 Projected Changes in Coastal Flooding Areas subject to flooding will increase: In years: 1.5 times present area In years: 2 times present area 13 Stormwater Design December 4, 2017

14 Combined Impact on Stormwater Analysis Higher coastal water levels diminish stormwater system performance Coastal Flooding Stormwater Conveyance Combined Flooding 14 Stormwater Design December 4, 2017

15 Changes in Rainfall Regional Precipitation Trends Heavy rainfall increasing Future precipitation conditions Up to 20% increase in design rain 15 Stormwater Design December 4, 2017

16 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 riseongoing work Stormwater Design December 4, 2017

17 Creating Comprehensive Stormwater Management Plans Comprehensive stormwater management plan means a plan, which may be integrated with other land use plans or regulations, that specifies how the water quality components, quantity components, or both of stormwater are to be managed on the basis of an entire watershed or a portion thereof. The plan may also provide the remediation of erosion, flooding, and water quality and quantity problems caused by prior development. VAC Chapter 60 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. 17 Stormwater Design December 4, 2017 Must be approved by DEQ

18 DEQ Energy Balance Equation/CSMP 18 Stormwater Design December 4, 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.

19 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. 19 Stormwater Design December 4, 2017

20 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 20 Stormwater Design December 4, 2017

21 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. 21 Stormwater Design December 4, 2017

22 Planning and Community Development/Development Services Center Stormwater 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 22

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 23

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 24

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 manmade channels December 5, 2017 Consultants, Builders and Developers Meeting 25

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 26

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 27

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 28

29 Experiences and Suggestions We are listening to you! December 5, 2017 Consultants, Builders and Developers Meeting 29

PRINCESS ANNE DISTRICT STORMWATER PROJECTS

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