Dead Run Stream Restoration Stream Team Kick Off August 18, 2015
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Dead Run Stream Restoration Stream Team Kick Off August 18, 2015
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Dead Run Stream Restoration Stream Team Kick Off August 18, 2015
- 1. A Fairfax County, VA, publication Department of Public Works and Environmental Services Working for You! Dead Run Segments 2/3 Stream Restoration Project Task Force Kick-Off Meeting McLean Government Center August 18, 2015
- 2. Dead Run Segment 2/3 Stream Restoration Project Stormwater Planning Division Discussion Outline 2 • Project limits • Project identification and regulatory drivers • Project benefits • Summary of approach in current concept design • Outline of proposed approach in new concept design • Review of completed stream restoration projects • Q&A
- 3. Dead Run Segment 2/3 Stream Restoration Project Project Limits 3 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 Stormwater Planning Division
- 4. Dead Run Stream Restoration Project Stormwater Planning Division Watershed Planning and Project Implementation • Dead Run has a drainage area just over 3 mi2 • 24 priority projects identified in the watershed management plan • Pond retrofits • LID Stormwater Enhancements • Stream Restoration • Neighborhood Stormwater Improvements 4 http://www.fairfaxcounty.gov/dpwes/watersheds/middlepotomac.htm
- 5. Dead Run Stream Restoration Project Stormwater Planning Division Watershed Planning and Project Implementation Project identified and prioritized by: • Physical conditions • Biological health • Flow and water quality data at U.S. Geological Survey stream gage on Dead Run at Whann Ave. • Location in watershed: Headwaters first = Upstream to Downstream • Watershed conditions 5 http://www.fairfaxcounty.gov/dpwes/stormwater/projects/project_list.htm
- 6. Dead Run Stream Restoration Segment 2 and 3 Stormwater Planning Division Existing Conditions 6
- 7. Stormwater Planning Division Dead Run Segment 2/3 Stream Restoration Project Existing Conditions - Biological Monitoring Data 7
- 8. Stormwater Planning Division Stormwater Program Regulatory Drivers – Local TMDL 8
- 9. Stormwater Planning Division Stormwater Program Regulatory Drivers • Virginia Stormwater Management Program (VSMP) – Municipal Separate Storm Sewer Permit (MS4) – Includes watershed planning and project implementation – Includes TMDL requirements for Chesapeake Bay and local streams • Total Maximum Daily Loads (TMDLs) – Chesapeake Bay – Local Streams – Establishes pollutant loading budget for a given impaired water body to meet water quality standards 9
- 10. Stormwater Planning Division Stormwater Program Regulatory Drivers – MS4 permit 10 Fairfax County’s MS4 Permit has requirements for the Chesapeake Bay and other (local) TMDLs – see excerpts below:
- 11. Stormwater Planning Division Dead Run Stream Restoration Project Benefits and Goals: • Improve water quality – Reduce sediment and nutrient loads • Stabilize stream banks to – Reduce stream bank erosion – Protect property – Reduce tree loss • Improve aquatic habitat and biological health • Restore and enhance vegetated stream buffer (riparian corridor) • Protect infrastructure: – Sanitary Sewer – Park Trails • Reduce frequent flooding, primarily along upper section of Segment 3 11
- 12. Stormwater Planning Division Dead Run Segment 2/3 Stream Restoration Project Estimated water quality benefits 12 • Chesapeake Bay Expert Panel protocols used for estimating stream restoration nutrient credits • For Total Phosphorus (TP) as an example the estimated reduction in loadings as a result of the proposed stream restoration for Segments 2/3 ranges from 0.063 to 0.261 lbs/LF/yr • This compares to a ‘default’ rate of 0.068 lbs/LF/yr. The high end of the estimated load reduction is 3X the default rate • Total annual estimated reduction in erosion for Segment 2/3 is between 783 to 1,500 tons/year and the estimated reduction in TP loading is between 190 and 788 lbs/year
- 13. Stormwater Planning Division Dead Run Segment 2/3 Stream Restoration Project Estimated flood reduction levels 13 Modeled reduction in flood elevations range from 1.2 ft. (2-YR storm) to 0.95 ft. (100-YR storm)
- 14. Stormwater Planning Division Dead Run Segment 2/3 Stream Restoration Project Overview of Approach used to Develop Current Concept 14 – 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
- 15. Stormwater Planning Division Dead Run Segment 2/3 Stream Restoration Project Alternative Approaches 15 – Re-walked the stream and buffer again – Priority/Option 2 and 3 Restoration Approach – Options for Refinement of the Design • Smaller Channel Cross-section in specific areas – Transition from smaller to larger channel sections in areas, where possible – Opportunities to save trees • Still focus on less frequent storm events and improving the impacts of flooding especially in the Segment 3 Upper area • Maintain overall channel stability
- 16. Stormwater Planning Division Dead Run Segment 2/3 Stream Restoration Project Alternative Approaches 16 • Smaller Channel Cross-section in specific areas – Transition from smaller to larger channel sections in areas, where possible – Opportunities to save trees
- 17. Stormwater Planning Division Dead Run Segment 2/3 Stream Restoration Project Alternative Approaches – Access 17 – Alternative 1 Approach • Proposed some access along the left bank of the stream through Reach 3 adjacent to Elizabeth Dr. – Alternative 2 Approach • Proposed access within the Park only, along the sanitary sewer easement and two sections of trail. No access on private properties. – Additional alternatives Explored • Access along sanitary sewer easement and trail. • Selecting route that has least amount of tree impacts. Fig. 1 Fig. 2
- 18. Dead Run Segment 2/3 Stream Restoration Project Stormwater Planning Division Stream Buffer Restoration Potential 18
- 19. Dead Run Segment 2/3 Stream Restoration Project Stormwater Planning Division Chesapeake Bay Preservation Ordinance Resource Protection Area (RPA) 19 http://www.fairfaxcounty.gov/dpwes/environmental/cbay/
- 20. Dead Run Segment 2/3 Stream Restoration Project Stormwater Planning Division Stream Buffer Existing Conditions 20
- 21. Dead Run Segment 2/3 Stream Restoration Project Stormwater Planning Division Stream Buffer Restoration Potential 21 Segment 3 Stream Buffer Concept Left Bank Left Bank Residential Residential 35 foot 50 foot 35 foot 50 foot Area (Acres) 1.14 1.55 0.46 0.87 Canopy Trees 114 155 46 87 Understory Trees 229 310 92 174 Shrubs 1,246 1,690 501 946 Estimate tree and shrub plantings for Segment 3: Left Bank Only Project Fact Sheets
- 22. Stormwater Planning Division More Information For additional information call Dipmani Kumar, P.E., CFM Project Manager 703-324-5500, TTY 711 dkumar@fairfaxcounty.gov www.fairfaxcounty.gov/dpwes 22
Notas do Editor
- STANTEC All approaches to design follow NCD Principals Based on the field study, we started with Priority 2 (aka Option 2) approach. To provide greatest improvement to channel stability, reduction of erosion and capturing of storm events to alleviate nuisance flooding. Goals to repair the benthics and biology in addition to reducing bed/bank erosion. Priority 2 Create New Floodplain and Stream Pattern Below the Historical Floodplain Elevation but Above Current Stream Elevation\ Priority 3 Widen FP at existing BF elev.
- STANTEC Priority 3 Widen FP at existing BF elev. Options for design refinement Priority 2 and 3 approach. Smaller channel XS vs Typical, 60 SF vs 90 SF in Seg 3 Upper for example. pros/cons (ie. Smaller channel section would disturb less land but would not address the flooding as much as the traditional channel design sizing we have no the plan now). We must incorporate the need to maintain some level of flood reduction for the folks living next to the upper section of Segment 3. This could potentially mean keeping the channel dimensions similar there while transitioning from a smaller channel section upstream and transitioning to a small channel section downstream, as long as the entire system remained stable. I’ll leave it up to you to explain the limitations of maintaining the flood reduction levels in the current concept for the upper section of Segment 3, while revising the upstream and downstream sections to minimize tree loss
- STANTEC Example of alt approach in Seg 2 – where a P3 bank stabilization and preservation approach is used. Minimize work in the channel as well.
- Fig 1 Small dark green circles identify trees saved along access route by adjusting the path. The access path (yellow) is ~15’ wide. The Blue is the proposed stream channel bankfull width. This study would have more trail overlaps. we have looked at alternative access routes, following the trail and sanitary sewer and from a quick study we see a way to at least 22 trees just be adjusting the access routes Fig 2 Small dark green circles identify trees saved along access route by adjusting the path. The access path (yellow) is ~15’ wide. The Blue is the proposed stream channel bankfull width.