This document summarizes a study of flood mitigation scenarios for Tripps Run at Barrett Road in Fairfax County, VA. Four scenarios were analyzed: 1) raising a bridge, 2) stream enhancements without property acquisition, 3) acquiring 9 properties for floodplain restoration, and 4) acquiring 16 properties for restoration. Scenario 3 provided the best balance of benefits, reducing flood levels by up to 4.6 feet, removing 13 structures from the floodplain, and costing an estimated $12.7 million. The consultants recommended pursuing additional information to support a decision on implementing Scenario 3.

1. A Fairfax County, VA, publication
Department of Public Works and Environmental Services
Working for You!
Tripps Run at Barrett
Road Flood Mitigation
Study
Project No. SD-000032-069
Mason District
February 18, 2021

2. Tripps Run at Barrett Road
Stormwater Planning Division
Study Objectives
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Assess the feasibility of various flood mitigation scenarios;
Develop corresponding environmental corridor and
restorative stream enhancement design features;
Quantify the associated flood reduction benefits; and
Develop planning level cost estimates.

3. Tripps Run at Barrett Road
Tripps Run – Existing Conditions
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Stormwater Planning Division
Portions of the channel
have been straightened
since 1947
Channel armor (riprap) in
bed and along banks
35 ft concrete trapezoidal channel
upstream of Annandale Rd
Lack of vegetation
(fences and backyards)
Poor access to
floodplain

4. Tripps Run at Barrett Road
Stormwater Planning Division
Stantec Study Scope
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Background Information and Field Visit
 SCENARIO 1 - Raise the Holloway Road bridge above the 1%-annual-chance water surface
elevation (WSE)
 SCENARIO 2 - Restorative stream enhancements without any property acquisition
 SCENARIO 3 - Acquire 9 properties and create an environmental corridor with restorative stream
enhancements
 SCENARIO 4 - Acquire 16 properties and create an environmental corridor with restorative
stream enhancements
Analysis of Scenarios
Floodplain Modeling and Mapping
Technical Memorandum
Report with Planning Level Cost Estimates

5. Tripps Run at Barrett Road
Location Map
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Annandale Road
Sleepy Hollow Road
Holloway Road
Dashiell Road
Barrett Road

6. Tripps Run at Barrett Road
Stormwater Planning Division
Existing Conditions
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Existing Conditions
FEMA Model from 2017, with refinements
• Additional cross-sections
• Incorporation of obstructions, restrictions,
and encroachments seen in field
• Channel roughness updates as seen in field
Results
Backwater from both Sleepy Hollow Road
bridge and Holloway Road bridge
1%-Annual-Chance WSEs 4 to 5 feet higher
than some house elevations

7. Tripps Run at Barrett Road
Stormwater Planning Division
Floodplain Mapping – Existing Conditions
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8. Tripps Run at Barrett Road
Stormwater Planning Division
S1 – Elevating Holloway Road Bridge
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Scenario 1 Results
Max 1%-Annual-Chance WSE decrease: 0.4 ft
(just upstream of former bridge location)
Bridge would need to be elevated an
additional 7.1 feet => Not feasible
 Raise Holloway Road Bridge above
1%-Annual-Chance WSE
No change to number of structures within
the mapped 1%-Annual-Chance floodplain
boundary

9. Tripps Run at Barrett Road
Stormwater Planning Division
S2 – Stream Enhancements, No Property Acquisition
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Scenario 2 Results
Max 1%-Annual-Chance WSE decrease: 0.8 ft
(just upstream of Dashiell Road)
WSE at Holloway Road Bridge: no change
WSE at downstream end of project: no
change
 No property acquisition
 No additional easements
 Stream enhancements
 Grading within existing County
easements and property

10. Tripps Run at Barrett Road
Stormwater Planning Division
Floodplain Mapping – Scenario 2, Stream Enhancements
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11. Tripps Run at Barrett Road
Stormwater Planning Division
Environmental Corridor – Scenario 3 & 4
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Demolish bridge at
Holloway Road
Improved floodplain
connectivity
Create passive recreation
area for the community
Grading floodplain and
overflow channel
Revegetate with native
species
Add riffles and grade
control features to stream

12. Tripps Run at Barrett Road
Stormwater Planning Division 12
Scenario 3 Acquired Properties
Scenario 3

13. Tripps Run at Barrett Road
Stormwater Planning Division
S3 – Environmental Corridor, Acquire 9 Properties
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Scenario 3 Results
Max 1%-Annual-Chance WSE decrease: 4.6 ft
(just upstream of Cofer Road)
WSE decrease at former Holloway Rd Bridge:
2.8 ft
WSE decrease just upstream of Dashiell Road:
2.8 ft
 9 properties acquired
 Environmental stream corridor
 Stream enhancements
 Overbank channel

14. Tripps Run at Barrett Road
Stormwater Planning Division
Scenario 3 & 4 - Concept
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Walking Path
Acquired
Properties
Stabilized
Stream with
Enhancements
Holloway Bridge
Removed
Environmental Corridor
w/Overflow Channel
Holloway
Road
Floodplain
Grading

15. Tripps Run at Barrett Road
Stormwater Planning Division
Floodplain Mapping – Scenario 3, Acquire 9 Properties
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*Structures acquired are not included in the count of
structures removed from floodplain.

16. Tripps Run at Barrett Road
Stormwater Planning Division 16
Scenario 4 Acquired Properties
Scenario 4

17. Tripps Run at Barrett Road
Stormwater Planning Division
S4 – Environmental Corridor, Acquire 16 Properties
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Scenario 4 Results
Max 1%-Annual-Chance WSE decrease: 4.7 ft
(just downstream of Dashiell Road)
WSE decrease at former Holloway Road
Bridge: 2.8 ft
As compared to Scenario 3, more significant
WSE reductions are seen in locations north of
Cofer Road
 16 properties acquired
 Environmental stream corridor
 Stream enhancements
 Overbank channel

18. Tripps Run at Barrett Road
Stormwater Planning Division
Scenario 4 - Concept
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Environmental Corridor
w/Overflow Channel
Acquired
Properties
Walking Path
Stabilized
Stream with
Enhancements
Floodplain
Grading

19. Tripps Run at Barrett Road
Stormwater Planning Division
Floodplain Mapping – Scenario 4 Acquire 16 Properties
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*
*Structures acquired are not included in the count of
structures removed from floodplain.

20. Stormwater Planning Division
Rendering
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Existing Conditions at Holloway Rd and Barrett Rd
6640, 6642, 6644,6646
6648, 6650 6652, 6654,
and 6656 Barrett Road

21. Stormwater Planning Division
Rendering
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Proposed Scenario 3 and 4 Rendering at Holloway

22. Tripps Run at Barrett Road
Stormwater Planning Division
Comparison
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Scenario Stream
Function
Enhancement
Max
Decrease
1%-Annual-
Chance
WSEL
Acquisitions Residential
Structures No
Longer within
1%-Annual-
Chance FP
Residential
Structures
Remaining in
1%-Annual-
Chance FP
Planning
Level
Costs
Scenario 2 Low 0.8 ft None 2 60 $1.6 M
Scenario 3 Moderate 4.6 ft 9
properties
13 40 $12.7 M
Scenario 4 High 4.7 ft 16
properties
17 29 $18.4 M
Consultant Recommendation
• Scenario 3 appears to optimize benefits, consistent with stated project goals.
• Commonly understood that more information can support more informed decision-
making. Recommendation on additional information to collect.

23. Additional Information
For additional information, please contact
www.fairfaxcounty.gov/publicworks
Tripps Run at Barrett Road
Stormwater Planning Division
Joni Calmbacher, Project Manager
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703-324-2183
Joni.Calmbacher@fairfaxcounty.gov