harford community stream restoration 2013

Wetland

Stream Restoration and The Upper Pohick creek

Watershed

Presented by Michael S. Rolband

P.E., P.W.S., P.W.D.

Wetland Studies and Solutions, Inc.

5300 Wellington Branch Drive . Suite 100 . Gainesville . Virginia 20155

www.wetlandstudies.com

Fairfax

County,

Virginia

Department of

Public Works

and

Environmental

Services

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Wetland Studies

and Solutions, Inc.

• Natural & Cultural Resource consulting firm

• 75 Staff

– Archeology, Engineering, Environmental Science & Ecology, Environmental Technology, Compliance, GIS, Regulatory, Surveying, & Wildlife Biology

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Why are we here ?

To discuss restoration of the “Harford” stream with the community

This area listed for restoration in the Pohick Creek Watershed Management Plan

- Project Number: PC9257

- Project Number: PC9258

PC9257

PC9258

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Why are we here ?

4

The stream is eroding.

The storm-water pond and emergency spillway need repair.

3.5’ headcut Eroded channel, vertical banks

Significant deposition in stormwater pond Emergency spillway failure

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• The Environmental Protection Agency Chesapeake Bay TMDL Plan Requires Fairfax County pollutant reductions

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Why are we here ?

• Erosion results in poor water quality; high levels of:

– Total Suspended Solids (TSS)

– Total Nitrogen (TN)

– Total Phosphorous (TP)

Poor water quality Good water quality

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Why are we here ?

• What has caused the erosion?

• What can be done to fix the erosion and prevent future issues?

Dahlgreen Pl tributary (PC9258)

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The urban watershed problem

Source: The Federal Interagency Stream Restoration Working Group

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Why restore ?

Reconnect to the existing floodplain to:

• Slow velocities

• Increase evapotranspiration

• Remove pollutants (TP, TN, and TSS)

• Improve riparian habitat

• Restore groundwater levels

After planting - 1999

Before restoration After restoration

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Design Methodology for Urban Streams

- Natural Channel Evolution -

Evolutionary process considers the channel’s incision, bank stability, & sedimentation load (aggrading or degrading)

Severe Poor Marginal Suboptimal Optimal

Severe Channel Condition Optimal Channel Condition

South Lakes High School Ellanore Lawrence Park

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Rural

Reston

Flo

w R

ate

(cfs

)

Drainage Area (sq mi)

Flow Rate vs Drainage Area

Urban Stream - Design Realities

1. Significantly more flow than rural streams.

2. Significantly more “bankfull” events than in rural watersheds.

3. Given site constraints, reinforcement is necessary.

• Rock structures – using native diabase rock

• Reinforced bed

• Heavy planting densities – native vegetation only

McLean Place (after 4.5 yrs) Snakeden Branch – Reach 3

(after 16 months)

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Stream Reinforcement

Reinforced Bed

Step Pools

Native Vegetation

Cross Vanes

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Restoration approaches

Priority 1 Restoration - Raise stream to reconnect with the floodplain.

Fewer trees removed

Width of disturbance

Balanced cut and fill volumes

result in less waste

Snakeden Branch Reach 2 – Priority 1 Restoration

Before After

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Priority 2 Restoration – Excavate floodplain at lower elevation.

Width of disturbance

Large cut volumes result in waste material

Many trees removed

Priority 3 Restoration – Confined stream valleys.

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Snakeden Branch Reach 2

(2003, by others) –

Long-term stability not

achieved using this

approach.

Priority 4 Restoration – Stabilize in-place


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Harford stream: Historic Conditions

1937

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1971 1972


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1979 1998


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2012


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Harford stream: Existing Conditions

• Drainage Area

121.1 acres

• Imperviousness

37%

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Culvert and rip rap channel

20


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Sediment deposition


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Riprap and deposition along paved path


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3.5’ head cut


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Debris, incised channel


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Existing bridge


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Exposed utility lines


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• Eroded channel approximately 5-ft deep

• Listed for restoration in watershed plan (PC9258)

Outfall from Dahlgreen Place


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Incised channel


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Culvert at Guinea Rd.

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Heavy deposition in sediment forebay


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Emergency spillway showing signs of failure


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What does fairfax county need from your

association ?

• Guidance from the community regarding:

• The desire for additional project meetings or stream walks

• Details of the Community Association approval process

• An easement to allow the County and its contractors to:

• Survey and develop restoration plans

• Restore the stream

• Maintain the stream

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• Pre-design Meeting (Tonight)

• Data Collection

• Stream Restoration Design Process

• Concept Plan Development

• Preliminary Design

• Final Design

• Pre-construction Review

• Construction

Plan Development Process

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• Obtain topography

• Survey locate & tag trees (> 8” dbh)

• Survey channel profile and cross-sections

• Sediment sampling

• Perform wetland delineations and obtain Jurisdictional Determinations (JD’s) from U.S. Army Corps of Engineers

Data collection

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Objective – Partnership between Fairfax County staff and the Lake Braddock Community

• Establish community representative(s) to coordinate with County staff as the project progresses

• Community involvement at all levels of the plan development process (Concept, Preliminary, Final Design, and Construction)

– Plan review, discussion, and feedback

community Involvement In the Plan

Development Process

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Stream restoration design process T

HE

DE

SIG

N P

RO

CE

SS

Determine Bankfull Width

and Bankfull Area to convey

current flows.

Apply Bankfull Width to

reference ranges of sinuosity

and meander radii.

Layout initial design

alignment (minimize impact

to infrastructure and trees)

Revise restoration design

and access

(based on citizen input)

Final Design

Citizen Meeting Citizen Meeting

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Tree impact considerations

Ecological / Habitat Value

• Size / Diameter

• Higher - Climax species: Oaks, Hickory, Holly (mast

producers, long-lived).

• Lower – Early successional species: Maples, Poplar

(fast-growing, short-lived).

Existing Condition

• Undercut by stream, high proportion of exposed

roots, short life expectancy

• Dead, dying, diseased, or damaged trees that pose a human safety hazard

• Impacting or pending impact to infrastructure (utilities, roads, trails, etc.)

Proposed Condition

• Drip line heavily impacted during restoration, minimal chance of survival, AND

• Human safety hazard to trails, houses, bridges, etc.

Stream restoration design process

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Short term impact for long term benefit

• Cleared trees “recycled” as in-stream habitat, grade control, wood-chip

trails, habitat “brush” piles, firewood

• Restoration raises the water table, (raises stream bed) which increases

stream access to floodplain and nutrient delivery to roots.

• Healthier ecosystem will develop with the density and species variety

of replacement plantings

– Mosquito population control via predator habitat

– Dense streambank planting will provide shade, reduce water

temperatures, increase oxygenation, increase fish survivability

– Dragonfly larva molting access via heavily planted streambank with

shallower slope

• Canopy loss will close as remaining trees adjust and react to increased

sunlight, growing to fill in openings

Fewer trees cut = lower restoration cost • Tree-climbing removal method vs. traditional forestry timbering

(minimize impacts to neighboring trees) is expensive.

Lower water table

Higher water table

Incised stream

Restored (raised) stream

Stream restoration design process

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Pre-Construction Construction

Post-Construction 5 Months After Construction

Examples - Snakeden Reach 2

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Examples - Snakeden Reach 3

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Pre-Construction

15 Months After Construction Post-Construction

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Examples – Snakeden reach 13

Post-Construction

Pre-Construction

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Pre-Construction Construction

Post Construction After plant establishment

Examples – Big Rocky Run Tributary

Post-Construction

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Examples - Sheffield

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Pre-Construction Post-Construction

Construction

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PLANTING – TREES & SHRUBS

Split into 2 planting zones:

- Riparian

- 1 gallon containers (planted at 640 plants/acre)

- both trees & shrubs

- Streamside

- live stakes/tubelings (planted 1ft o.c.)

- shrubs (planted 3 ft o.c.)

Tree Species: Pin Oak, Willow Oak, White Oak, Swamp White

Oak, Northern Red Oak, Sweet Gum, Black Gum, River

Birch, Sycamore, Red Maple, Box Elder, and Black Willow.

Shrub Species: Silky Dogwood, Southern Arrowwood,

American Holly, Service-Berry, Black-Haw, Eastern Redbud,

Elderberry, Flowering Dogwood, and Brookside Alder,

Hazelnut, Northern Spicebush, Black-Haw, Winterberry.

Eastern Redbud

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PLANTING - Riparian Seed Mix

• Tree Species

• Musclewood

• Black Gum

• American Sycamore

• Red Maple

• Eastern Redbud

• Flowering Dogwood

• Forbs

• Oxeye Sunflower

• Joe-Pye Weed

• Grass Leaved Goldenrod

• PLUS 24 additional species!

• Shrub Species

• Witch Hazel

• Winterberry

• Southern Arrow Wood

• Northern Spicebush

• Canadian Serviceberry

• Black Chokeberry

• Black-Haw

• Grass Species

• Squarrose Sedge

• Riverbank Wild Rye

• Foxtail Millet

• PLUS 8 additional species!

• Applied at a rate of 125 lbs/acre

• Custom mix

• Consists of native species found in a healthy, diverse NOVA ecosystem:

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Greater Biodiversity

• Mature forest continues to provide habitat for raptors, woodpeckers, bats and deer

• Recently planted areas provide habitat for small mammals, song birds, fox and deer

• All species benefit from the “edge effect”

• Restored stream allows detrital input to be processed, thus increasing stream health and function

Orchard Oriole

Red-shouldered Hawk

Cottontail Rabbit

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technical review

• Fairfax County Department of Public Works and Environmental Services

• US Army Corps of Engineers

• Virginia Department of Environmental Quality

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Conclusion

1. The “Harford” tributary of the Pohick Creek Watershed is severely degraded due to urbanization – a situation made worse by inadequate stormwater management.

2. Fully restored streams will provide long-term stability, improved aesthetics, & greater open space usability.

3. Short-term construction disturbance will provide long-term societal and ecological benefits to a heavily used, urban stream valley network.

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Questions?

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For more information

• 703-324-5500, TTY 711

• [email protected]

• www.fairfaxcounty.gov/dpwes/stormwater

• A Fairfax County, Virginia

publication, April 2013

50

mailto:[email protected]

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

harford community stream restoration 2013

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