http://www.fairfaxcounty.gov/

Dredging Program and Project Background

Project Benefits

Royal Lake Conditions

Phased Approach

Dredging Methods and Alternatives

Park Access and Community Coordination

Next Steps

Royal Lake: Meeting Agenda

History

– Lakes previously dredged by DPWES Stormwater

– Limited to small quantities

– Dewatered on site

Lake Barton completed in 2011

Currently working on:

– Huntsman Lake, Woodglen Lake, Royal Lake

Dredging and Lake Restoration Program

Completed Data Collection

Developing Lake Dredging and Management Plan

Community coordination at design and construction phases

– Preliminary Design (65%)

– Final Design (95%)

– Preconstruction: Pardon Our Dust meeting

December 2013: Final Design

Construction in Fiscal Year 2015 (July 2014)

Royal Lake Dredging and Restoration Project Timeline and Coordination

Restore sediment pool capacity

– Downstream water quality benefits

– Lake water quality

– Aesthetics

Improve lake water quality and habitat

Provide long term maintenance improvements

Project Goals and Benefit

Lake Barton Dredging and Restoration

Area Treated (acres)

Phosphorous Removal Nitrogen Removal Sediment Removal

544 77,000 lbs dredged 115,500 lbs dredged 38,500 tons dredged

Annual benefit from increased trapping

efficiency

130 lbs/year 200 lbs/year 65 tons/year

Royal Lake Facts

Drainage area = 2,477 acres (3.67 square miles)

Lake surface area = 37.5 acres

Sediment pool capacity = 416,000 cubic yards (CY)

Current sediment in lake = 100,400 CY

Estimated annual sediment load = 4,400 CY

50 feet

100,400 CY

Royal Lake

Royal Lake: Sediment Thickness

Royal Lake: Water Depth

Royal Lake: Dredging Areas

Phase 1: Base Dredge = 40,000 CY

Phase 2: Up to an additional 60,000 CY

Zone D

12,400 CY

Royal Lake: Partial Drawdown

Dredging Methods and Alternatives

1. Mechanically dredge deposited sediment and haul wet

2. Drain lake and dry deposited sediment in place before hauling

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

Lake Barton Example

Lake Barton Example: Pre-Dredging

Lake Barton Example: Dredging in Progress

Dredging: Dredging took place without draining the lake.

Lake Barton Example: Dredging in Progress

Lake Barton Example: Disposal Site

North Park Lake Example Allegheny County, Pennsylvania

Dredging: The lake was drained and the sediment was dried in-place.

North Park Lake Example Allegheny County, Pennsylvania

Temporary Diversion Channels

Equipment Working on Next Slide

North Park Lake: Dredging Allegheny County, Pennsylvania

Truck Wash

Temporary Diversion Channel

Low Pressure Excavator

Bulldozer

Bulldozer

Excavator and Dozer Truck Access

Staging

General Sequence – Establish access and staging areas – Conduct dredging utilizing barges – Haul wet sediment to disposal site

for drying

Benefits – Less weather dependent – Quicker initial start to dredging – Less potential for schedule

extensions or delay

Concerns – Increased sediment handling effort

at disposal area – Potentially higher cost

Dredge Alternative – In the Wet

General Sequence – Initiate drawdown of lake – Establish access and staging areas – Establish diversion channels within lake – Conduct dredging

Benefits – Higher daily sediment removal rates – Minimal sediment handling effort at disposal

area – Potentially lower cost

Concerns – Very weather dependent – Higher potential for delays due to weather – Typically more odor from sediment exposed – Need to relocate/salvage fish

Dredge Alternative – In the Dry

In-lake forebay

Wetland planting

Shoreline stabilization

Fish habitat

Fish stocking

Lake Restoration

Fish habitat created from salvaged trees

Lake Barton: Fish stocking by Virginia Game and Inland Fisheries

Royal Lake: Shoreline Restoration

Royal Lake: Shoreline Restoration

Royal Lake Existing Conditions

Shoreline Protection Options

Fish Habitat Structures

Royal Lake: Site Access and Staging

Optional?

Royal Lake: Site Access and Staging

Staging Area 1 Potential Expansion

Berm/Cofferdam to be built

Area to be dewatered and backfilled to expand staging area after berm/cofferdam is built

Royal Lake: Dewatering Basin

Inactive Dewatering Basin

Access During Construction

Public Access: The park will remain open and existing parking lot will be available.

Access During Construction

Public Access: Pedestrian gates will be provided. Access through work areas and trails around the lake after work hours.

Community coordination at design and construction phases

– Preliminary Design (65%)

– Final Design (95%)

– Preconstruction: “Pardon Our Dust” meeting

December 2013: Final Design

Construction in Fiscal Year 2015 (Starts July 2014)

Project Duration:

– Phase 1, Base Dredge: Dredge 40,000 CY = 5 to 6 Months

– Phase 2, Full Dredge: 9 to 12 Months

Royal Lake Dredging and Restoration Project Timeline and Coordination

Contacts:

Martin Chang, Project Manager 703-324-5825 | Martin.Chang@fairfaxcounty.gov

Dipmani Kumar, Section Chief 703-324-4612 | Dipmani.Kumar@fairfaxcounty.gov

http://www.fairfaxcounty.gov/dpwes/stormwater/

Royal Lake Dredging and Restoration

http://www.fairfaxcounty.gov/NVSWCD/ http://www.fairfaxcounty.gov/parks/