Dead Run Stream Restoration Public Meeting May 19, 2015

A Fairfax County, VA, publication

Department of Public Works and Environmental ServicesWorking for You!

Dead Run Segment 2/3 Stream Restoration Project

Public Meeting

McLean Community Center

May 19, 2015


Stormwater Planning Division

Meeting Outline

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• Project Scope and Status• Plan Summary and response to citizen comments• Concept Plan Overview

– Basis for design– Tree save options– Floodplain analysis and review of more frequent storm impacts– Buffer restoration measures– Examples

• Next Steps• Q and A• Walk to site



Project Limits

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Segment 2 – McLean Central Park

• 800 Linear Feet

• Completely in Park

• Starts below previously restored section near library

Segment 3 – Dead Run Stream Valley Park

• 1,500 Linear Feet

• Extends to Churchill Road

• Residential lots along Elizabeth Drive and Carol Rayes Street



Project timeline

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• Project initiated: Fall, 2013

• Surveys and assessment completed: Winter, 2013

• Pre-concepts submitted: April, 2014

• First public meeting – April 23, 2014

• Field walk with FCPA, MTA, Urban Forestry – August 15, 2014

• Pre-concept revisions to minimize tree loss completed: February, 2015

• Second public meeting – February 18, 2015

• Revised concept plan with alternative access options for Segment 3: completed May 12, 2015

• First field walk with community – May 19, 2015

• Second field walk with community – June 9, 2015



Overview of Plans

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• _PG1-27.pdf: Existing and proposed conditions (plan, profile, and cross-sections)

- Plan: Bird’s eye view

- Profile: Change in elevations along the proposed stream channel centerline

- Cross-sections: View of a section taken perpendicular to the channel centerline at a particular location.

• _PG28-31a.pdf: Plan view of access with and without aerial photography background – two options for Segment 3

• _PG32-43.pdf: Hydrology (flows) summary, and hydraulics (water surface elevations) of existing and proposed conditions

• Excel files: Tree inventory – diameter, condition, removal status



Summary of comments received

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• Need to understand full scope of project:

• Access points, how they will be secured, personal liability if county seeks to access our property (_PG28-31a)

• Type/Size of equipment that will be used (Do not dictate means and methods, equipment proposed by contractor can be shared by contractor at Pardon Our Dust meeting)

• Consideration of alternative modes of accessing creek that could reduce impact on foliage (_PG28-31a – also discussed in detail later)

• Duration of project, hours of construction, how long neighborhood will be denied access to pathways (Estimated 6-9 months, Standard work hours are 7am – 5 pm. Loss of access to trails will be minimized to the extent possible)




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• Need to understand full scope of project:

• Any revision to path of creek (_PG1-27.pdf)

• Impact on topography and what type of approach will be used in what parts of creeks (terracing, widening) (_PG1-27.pdf)

• Commitment of funding for replacement of lost trees and maintenance by county to ensure trees survive (_PG28-31a)

• Aesthetic impact of sediment erosion techniques. (Erosion and Sediment controls are detailed as part of the final plans, all structures proposed to be installed are shown in the plan and profile).




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• How flooding concerns will be addressed:

• Creek jumps the bank a few times a year and threatens to flood homes

• Danger of flash floods in the park, property of nearby residences, and Churchill Road bridge

(_PG32-43.pdf, also discussed in detail later)

Recurrence

Interval Probability

100-year 1%

10-year 10%

2-year 50%

1-year approaches 100%




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• How flooding concerns will be addressed (continued):



Churchill Road Bridge Flooding

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• VDOT inspection reports indicate no deficiencies with the bridge.• No current or future project planned for the bridge. • Not subject to frequent closures because of overtopping.




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• Loss of tree canopy:

• Desire strong measures to maintain and preserve the existing canopy

• Anticipated tree impacts shown on plan sheets – 6-12” tree impacts for Segment 3 access options being updated

• Tree save efforts discussed in detail later

• Proposed buffer restoration measures discussed in detail later

1 Basis for Design

• Stable Channel

• Understanding of

Floodplain

• Address Erosion

1 Basis for Design • Natural Channel Design (NCD) Approach – reference reach, analytical,

regional relationships and hydraulic analysis

• Stream pattern, profile and section

• Range of values for stable stream pattern

• Tree loss is unavoidable but provides opportunity to improve riparian diversity

1 Basis for Design

• Establish Goals:

• 1. Improve Flow Conditions in the Channel through Adjustments to Plan/Profile/Section

• 2. Create a Stable Channel by Reducing Bed/Bank Erosion that has Benefit of Reducing Contributions of Nitrogen and Phosphorus (i.e. Water Quality Improvement)

• 3. Improve Channel Geomorphology and Opportunities for Species Diversity (i.e. Use Structures to Stabilize Channel and Create Pool Habitats)

• 4. No-Rise / No-Impact of the Floodplain

2 Tree Save Efforts

12” and Larger Trees:

• ~557 trees 12” and larger assessed

• ~43 trees 12” and larger are “at risk”

• Species: ~32% tulip tree, ~27% red maple, ~7% green ash

6-12” Trees:

• ~214 trees 6-12” assessed

• ~28 trees 6-12” are “at risk”

• Species: ~23% red maple, ~21% boxelder, ~18% slippery elm, ~11% green ash

2 Tree Save Efforts

• Pre-Concept Plan (Feb. 2014) = ~137 trees 12” and larger removed. This was same plan walked in August 2014.

• Concept Plan (Feb. 2015) = ~110 trees 12” and larger removed. Initial alternative access options developed.

• Since Feb. 2015 meeting, we’ve modified the channel layout and access options, and located 6 to 12” size trees.

2 Tree Save Efforts

Some of the saved trees

3 Access Options

• Current Plan (May 2015) = ~88 trees 12” and larger proposed

for removal, of which ~23 are “at risk”. Up to 10 additional

trees could be removed due to access. ~133 trees 6-12”

proposed for removal, of which ~28 are “at risk”. Up to 20

additional trees could be removed due to access.

• 12” and Larger Trees species most affected:• ~24% tulip tree, ~20% red maple, ~17% green ash

• 6-12” Trees most affected:• ~20% red maple, ~27% boxelder, ~20% slippery elm, ~13% green ash

• Woody vegetation should not be in the sanitary easement and is subject to removal by Wastewater at any time.

3 Access Options

Segment 2

Tree DEC474 has been removed

3 Access Options

Segment 3 Alternative 1

Removals due to access are primarily on the left bank. ~9 trees (~2 >12” and ~7 6-12” size)

Trees DEC91 & DEC301 have been removed

3 Access Options

Segment 3 Alternative 2

Removals due to access are primarily on the right bank. ~21 trees (~7 are >12” and ~14 are 6-12” size) – most are within the sanitary easement

4 Floodplain Analysis• Studied more frequent storm events 1-, 2-, 10- year flows

• Studied less frequent storm events 50-, 100- year flows

• No-Rise / No-impact to the floodplain

• See pages 32-43 of plan

4 Floodplain Analysis

Pre/Post Comparison – Existing Section 13552 year flow out of banks

• Existing Conditions Analysis


Pre/Post Comparison – Existing Section 1355Proposed Channel and Nested Channel


Pre/Post Comparison 100 and 10 yearTypical Channel Section



Stream Restoration Pictures

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Government Center Stream Restoration - Before and After



Stream Restoration Pictures

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Poplar Springs, Burke - Before and After

Stream Restoration

Stormwater Management

Dead Run at Dolley Madison Library

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Stream Restoration


Dead Run at Dolley Madison Library

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August 2014 Right

January 2010 Below



Stream Buffer Restoration Potential

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Chesapeake Bay Preservation Ordinance

Resource Protection Area (RPA)

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http://www.fairfaxcounty.gov/dpwes/environmental/cbay/

http://www.fairfaxcounty.gov/dpwes/environmental/cbay/



Stream Buffer Existing Conditions

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Stream Buffer Restoration Potential

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Segment 3 Stream Buffer Concept



Stream Buffer Restoration - Example

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Typical Planting Area

County Staff will coordinate with individual homeowners on plant selection and placement on their properties

Buffer Parameters

35’ Minimum from edge of stream bank

50’ Offset optional

Plant density determined by Chesapeake Bay PreservationOrdinance

Dense planting will provide privacy screening and help mitigate tree loss




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Shrub Layer

Typical ShrubSpecies

SpicebushAmerican ElderberryWitch HazelWinterberry HollySilky DogwoodButton Bush




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Understory Trees

Typical UnderstorySpecies

Sweetbay MagnoliaEastern RedbudAmerican HornbeamHazel AlderSlippery ElmSassafras



Stream Buffer Restoration

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Canopy Layer

Canopy Tree

EvergreenUnderstory

Tree

DeciduousUnderstory

Tree

ShrubTypical CanopyTree Species

Sugar MapleRiver BirchAmerican BasswoodCommon PersimmonSwamp White OakPin OakWillow OakBlack Gum



Next steps with target dates

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• Receive concept design comments by June 19th, 2015

• Compile comments, finalize concept plans and publish to website by July 10th, 2015

• Develop 95% design plans, permitting by September, 2015

• Final design phase public meeting, October, 2015

• Final plan authorization and bidding phase – TBD based on funding and approved budget

• Target is late spring/early summer, 2016

• Sequence with Dead Run Segment 1 (Dominican Retreat)

• Pardon Our Dust meeting with residents and contractor before issuing construction notice to proceed.

Additional Information

For additional information, please contact

www.fairfaxcounty.gov/dpwes


Stormwater Planning Division 42

Dipmani Kumar

703-324-5500

[email protected]

Dead Run Stream Restoration Public Meeting May 19, 2015

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