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Huntington Levee Community Meeting

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Huntington Levee Community Meeting …

Huntington Levee Community Meeting

January 16, 2014

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  • 1. Huntington Levee Community Meeting January 16, 2014 Building Design Branch 1
  • 2. Purpose of Meeting • Review levee conceptual design features and recommendations • Receive feedback from the community on project features before moving forward with final design Building Design Branch 2
  • 3. Agenda I. Project Background II. Conceptual Design Features III. Accreditation IV. Questions Building Design Branch 3 3
  • 4. Project Background • June 2006 -160 homes were flooded from a storm event • 2009 – US Army Corps of Engineers (USACE) completed a study to evaluate flood damage reduction measures in the Huntington Community Building Design Branch 4 4
  • 5. Project Background • September 2011- Tropical Storm Lee caused damage to 160 homes in the Huntington Community • November 6, 2012 – Fairfax County voters approved stormwater bond referendum to fund design and construction of flood damage reduction measurers • November 9, 2012 – Fairfax County advertised for consultant design services • June 2013 – Fairfax County awarded the levee design contract to ARCADIS Building Design Branch 5 5
  • 6. Project Background Building Design Branch 6 6
  • 7. Project Background • November 2013 – ARCADIS submitted the Phase I design package to Fairfax County • Survey – 300 acre of aerial survey, 80 acre field survey, 26 field run cross sections of Cameron Run, utility survey • Geotechnical Investigation – collection and analysis of 13 additional soil borings • Wetland delineation • Conceptual Design • Review USACE 2009 study and conceptual design • Evaluate potential refinements/alternatives Building Design Branch 7 7
  • 8. Project Background • Phase II (January 2014-Winter 2017) • • • • • • Schematic Design (30%) Design Development (60%) Permitting Land Acquisition Construction Documents (100%) Bidding • Phase III (Winter 2017-Spring 2019) • Construction • Original schedule condensed by 7 months Building Design Branch 8 8
  • 9. Conceptual Design Features Key Design Considerations • • • • Collection Drains vs. Cut Off Wall Pump Station Location Stormwater Diversion Earthen Levee vs. Earthen Levee/I-Wall Combination Building Design Branch 9 9
  • 10. Collection Drains vs. Cutoff Wall Collection Drain (Recommendation) Pros • Lower cost • Ease of construction Cut Off Wall Cons • Maintenance of toe drainage pipe Pros • No maintenance of toe drainage • Higher risk of piping thru levee due to clogging of toe drain • Reduced risk of piping thru levee • Additional pumping capacity required (6,700 gpm) Cons • Higher cost • Specialized construction • Concern that it could raise groundwater levels and flood basements Building Design Branch 10 10
  • 11. Potential Pump Station Locations Central SWPS Location Westside SWPS Location Eastside SWPS Location Building Design Branch 11 11
  • 12. Potential Pump Station Locations Center of Levee Western End Property requirements Property requirements • Fairfax owned park property • Adjacent commercial parcel is ideal, but prohibitively costly • Would occupy space otherwise available for the excavated ponding area or park recreation area Permanent Access • From Liberty Dr. over raised road through excavated ponding area - Very exposed during storm events, safety concern Neighbor concerns / buffering • In center of neighborhood park recreation area • Very visible from neighborhood Drainage Permanent Access • Easy access off Fenwick Dr. or new access road from Metroview Pkwy. Neighbor concerns / buffering • Very close to homes at Fenwick Dr. Drainage Eastern End (Recommendation) Property requirements • Fairfax owned park property Permanent Access • New access road from Hunting Creek Rd. Neighbor concerns / buffering • Far from residential properties in Huntington Neighborhood • Buffered by wooded area • Divert all flow to Western end • Backs up to apartment complex recreation area • Slightly smaller diversion channel than Eastern option Drainage • Divert all flow to Eastern end • Slightly larger diversion channel than Western option • Requires a third channel to Cameron run with additional wetlands impacts and maintenance Building Design Branch 12 12
  • 13. Stormwater Diversion Building Design Branch 13 13
  • 14. Stormwater Diversion Options Grass Lined Drainage Ditch Concrete Drainage Ditch Precast Concrete Box Culvert • Erosion concern from high flow velocities • Not as wide due to steeper side slopes (1:1 = 15’-20’ or vertical = 10’) • Fence to prevent access • High construction cost for cast in place • Less maintenance than grass lined *Recommendation • 30’ wide @ 2:1 side slopes • Maintenance concerns and mowing • Standing water concerns due to flat grades • Lowest installation cost • Limited access points – security bars to prevent entry • Buried – any potential standing water is not exposed • Precast construction – culvert segments trucked to site • Maintenance - confined space entry Building Design Branch 14 14
  • 15. Earthen Levee vs. Earthen Levee/Wall Combination Earthen Levee Earthen Levee / I-Wall Combination (Recommendation) Pros • More natural aesthetic Pros • Reduced construction traffic • Clear access to Cameron Run • Lower cost Cons • Higher cost • Smaller overall levee mass, width reduced by 17’ • Reduced backwater impacts • Generates greater construction traffic • Reduced impact to trees • Greater overall levee mass, width varies from 60 feet – 85 feet Cons • Maintenance of wall • Access thru wall Building Design Branch 15 15
  • 16. Earthen Levee/Wall Combination Examples Architectural Facades Building Design Branch 16 16
  • 17. Levee Cross Sections Earthen Levee Earthen Levee / I-Wall Combination Building Design Branch 17 17
  • 18. Earthen Levee/Wall Combination Building Design Branch 18 18
  • 19. Earthen Levee/I-Wall Combination Building Design Branch 19 21
  • 20. Accreditation • Levee will be designed to meet FEMA accreditation standards • Fairfax County will submit an accreditation package to FEMA for their consideration Building Design Branch 20 22
  • 21. Questions  Contact Information – Huntington Levee Project  Phone #: 703-324-5800  Email address: HuntingtonLevee@fairfaxcounty.gov  Contact Information – Stormwater Questions  Phone #: 703-324-5821  Email address: SWPDmail@fairfaxcounty.gov  Huntington Levee Website: www.fairfaxcounty.gov/dpwes/huntingtonlevee To request this document in an alternate format call 703-324-5800, TTY 711. Building Design Branch 21 23