Huntsman Lake Dam Rehabilitation Project Huntsman Lake Dredging and Restoration Department of Public Works and Environmental Servcies

1. Huntsman Lake Dam Rehabilitation
Huntsman Lake Dredging and Restoration
Department of Public Works and Environmental Services
Fairfax County, VA
A Fairfax County, VA publication September 2012

2. Huntsman Lake Dam Rehabilitation
Huntsman Lake Dredging and Restoration
Outline
• Dam Rehabilitation
– Background
– Major design elements
– Easements
– Mitigation for tree and wetland loss
• Lake Dredging and Restoration
– Sedimentation
– Dredging options and approach
– Lake restoration
• Timeline for Projects and Coordination

3. Huntsman Lake Dam Rehabilitation Project
Background
• Huntsman Lake Dam is a 41.5 feet high earth‐fill dam built in 1973 as flood‐control
dam by the Natural Resources Conservation Service (NRCS). Fairfax County and the
Northern Virginia Soil and Water Conservation District (NVSWCD) were the local
sponsors.
• It was the second of six dams built by the NRCS in the Pohick Creek watershed

4. Huntsman Lake Dam Rehabilitation Project
Background
• The dam drains an area of 1,482 acres (2.3 square miles)
• Land‐use in the drainage area is 73 percent residential and 22 percent
woodland or open space

5. Huntsman Lake Dam Rehabilitation Project
Background
• The dam impounds a 28.6 acre lake at normal pool, with a floodwater
retarding pool area of 60 acres
• Huntsman Lake Dam is regulated by the Virginia Department of Conservation
and Recreation (DCR), Division of Dam Safety

6. Huntsman Lake Dam Rehabilitation Project
Background
• Huntsman Dam operates under a conditional Operation & Maintenance
(O&M) Certificate from DCR because its auxiliary spillway can only convey
about 50 percent of the flows from the design storm.

7. Huntsman Lake Dam Rehabilitation Project
Background
• In 2010, NRCS in collaboration with Fairfax County and NVSWCD initiated a rehabilitation
project for the Huntsman Lake dam
• Fairfax County contracted with Schnabel Engineering to provide engineering and ancillary
services for the project
• A local task force was formed to provide input on community concerns, and a number of
task force meetings and public meetings were held in 2010 and 2011
• A rehabilitation plan was developed by NRCS collaboratively with Fairfax County and
NVSWCD and released in September 2011
• Design work by Schnabel Engineering was initiated shortly after the release of the
rehabilitation plan, and a final design submitted in August, 2012

8. Huntsman Lake Dam Rehabilitation Project
Summary of rehabilitation plan

9. Huntsman Lake Dam Rehabilitation Project
Major Design Elements

10. Huntsman Lake Dam Rehabilitation Project
riser replacement

11. Huntsman Lake Dam Rehabilitation Project
riser replacement

12. Huntsman Lake Dam Rehabilitation Project
spillway realignment and armoring

13. Huntsman Lake Dam Rehabilitation Project
spillway realignment and armoring

14. Huntsman Lake Dam Rehabilitation Project
spillway realignment and armoring

15. Huntsman Lake Dam Rehabilitation Project
Easements
A public hearing for the required easement on Lakewood Hills
Community Association #1 property is planned for December 4, 2012

16. Huntsman Lake Dam Rehabilitation Project
mitigation for tree and wetland loss

17. Huntsman Lake Dam Rehabilitation Project
Summary
• In 2010, NRCS in collaboration with Fairfax County and NVSWCD
initiated a rehabilitation project for the Huntsman Lake dam
• Final design for the project has been completed by Schnabel
Engineering and is awaiting approval by NRCS and Fairfax County
• Permit applications have been prepared for the project and will
be submitted shortly
• A public hearing for an easement required on Lakewood Hills #1
Homeowners Association property is proposed for December 4th,
2012
• Mitigation for tree and wetland loss as a result of the project is
proposed on the lake shoreline and on Middle Run upstream of
Huntsman Boulevard

18. Huntsman Lake Dredging and Lake Restoration
Background

19. Huntsman Lake Facts
• Drainage Area = 1,482 acres (2.3 square miles)
• Lake Surface Area = 28.6 acres
• Sediment Pool Capacity = 295,000 cubic yards (CY)
• Current sediment in lake = 65,000 CY
• Estimated annual sediment load = 2,970 CY
32.5 feet
65,000 CY

20. Sediment Thickness

21. Water Depth

22. Inactive
Dewatering Basin
2011

23. Lake Restoration and Dredging Project
Project Goals
• Restore sediment pool capacity
– Downstream water quality benefits
– Lake water quality
– Esthetics
• Improve lake water quality and habitat
• Provide long term maintenance improvements

24. Dredging Alternatives
1. Mechanically dredge and
haul wet
2. Drain lake and dry in place
before hauling
3. Hydraulically dredge and
dewater on shore in Geo-
textile bags

25. Lake Barton Example
PRE‐DREDGING: An estimated 35,000 cubic yards of sediment accumulated in the lake
forming islands and reducing water levels to less than three feet in most areas.

26. Lake Barton: Pre-Dredging

27. Lake Barton: Dredging in Progress

28. Lake Barton: Dredging in progress

29. Lake Barton: Dredging in progress

30. Lake Barton: Completed Project

31. Option to Drain Lake
Lake Needwood in Montgomery County, MD

32. Option to Drain Lake

33. Option to Drain Lake
Lake Needwood in Montgomery County, MD
33

34. Huntsman Lake
Phase 1 Dredging 30,000 Cubic Yards

35. Huntsman Lake
Phase 2 Dredging up to an additional 35,000 Cubic Yards

36. Lake Restoration
• In‐lake forebay
• Wetland planting
• Shoreline stabilization
• Fish habitat
• Fish stocking
Lake Barton: Fish stocking by Virginia Game and Inland Fisheries
Fish habitat created from salvaged trees

37. Shoreline Restoration

38. Shoreline Restoration
Huntsman Lake Existing Conditions

39. Shoreline Protection
Options

40. Fish Habitat Structures

41. Huntsman Lake
Site Access and Staging Area

42. Huntsman Lake
2011

43. Huntsman Lake Dam Rehabilitation
Huntsman Lake Dredging and Restoration
Project timeline and coordination
• Project agreement between Fairfax County, NVSWCD and NRCS
(for dam rehabilitation) expected to be executed by
February/March, 2013
• Project bidding and contract award: approximately 2‐3 months
• Project duration: 8‐9 months
• Lake will remain drained for entire project
• Drawdown will be controlled to allow fish to migrate downstream
to the greatest extent possible
• Dam rehabilitation and dredging projects will be coordinated to
minimize the time lake is drained
• Lake filling after project completion is dependent on rainfall
conditions

45. Huntsman Lake Dam Rehabilitation
Huntsman Lake Dredging and Restoration
For more information or to request this information in an alternate
format, call the Stormwater Planning Division, Department of Public
Works and Environmental Services, Fairfax County 703‐324‐5500
TTY 711 or email SWPDmail@fairfaxcounty.gov