Huntsman Lake Dam Rehabilitation Project

Huntsman Lake Dam RehabilitationHuntsman Lake Dredging and Restoration

Department of Public Works and Environmental Services Fairfax County, VA

A Fairfax County, VA publication September 2012

• 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


Outline

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


• 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


• 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


• 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.


• 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

Huntsman Lake Dam Rehabilitation Project Summary of rehabilitation plan

Huntsman Lake Dam Rehabilitation Project Major Design Elements

Huntsman Lake Dam Rehabilitation Project riser replacement

Huntsman Lake Dam Rehabilitation Project riser replacement

Huntsman Lake Dam Rehabilitation Project spillway realignment and armoring



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

Huntsman Lake Dam Rehabilitation Project mitigation for tree and wetland loss

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

Huntsman Lake Dredging and Lake Restoration Background

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

Sediment Thickness

Water Depth

2011

Inactive Dewatering Basin

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

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

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.

Lake Barton Example

Lake Barton: Pre-Dredging

Lake Barton: Dredging in Progress

Lake Barton: Dredging in progress

Lake Barton: Dredging in progress

Lake Barton: Completed Project

Option to Drain LakeLake Needwood in Montgomery County, MD

Option to Drain Lake

33

Option to Drain LakeLake Needwood in Montgomery County, MD

Huntsman LakePhase 1 Dredging 30,000 Cubic Yards

Huntsman LakePhase 2 Dredging up to an additional 35,000 Cubic Yards

Lake Restoration

• In‐lake forebay• Wetland planting• Shoreline stabilization• Fish habitat• Fish stocking

Lake Barton: Fish stocking by Virginia Game and Inland FisheriesFish habitat created from salvaged trees

Shoreline Restoration

Shoreline RestorationHuntsman Lake Existing Conditions

Shoreline Protection Options

Fish Habitat Structures

Huntsman LakeSite Access and Staging Area

2011

Huntsman Lake


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


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 [email protected]

News & Politics

Huntsman Lake Dam Rehabilitation Project