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Case Studies of Floodplain and Stream Restoration

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Case Studies of Floodplain and Stream Restoration (FSR) Projects and their Potential Use for Flood Hazard Mitigation and Community Resiliency Presented by: Rich Pfingsten, PWS Stantec Consulting Services Inc. May 23, 2019 Goals & Objectives • FSR for Hazard Mitigation and Community Resiliency • Review of Basic Geomorphic Principles • Natural Channel Design Overview • Vane & Grade Control Structures • Floodplain and Habitat Features • Case Studies of Floodplain and Stream Restoration (FSR) Projects FSR for Hazard Mitigation & Community Resiliency FSR for Hazard Mitigation • Hazard Mitigation is any action taken to reduce or eliminate long- term risk to life and property from a hazard event. • FEMA encourages communities to incorporate methods to mitigate impacts of climate change into eligible Hazard Mitigation Assistance (HMA) funded risk reduction activities. • FSR projects are designed to be self-sustaining and are eligible for HMA funding to mitigate for: • Erosion • Flood Risk • Flood Reduction • Drought Mitigation FSR for Hazard Mitigation & Community Resiliency FSR for Community Resilience • Community Resiliency is defined as the ability of a community to: • Adapt to Changing Conditions including Climate Change • Withstand Disruption • Recover from Emergencies • FSR projects have the capacity to provide resilience to threats and hazards to multiple Ecosystem and Natural Resource issues: • Water/Hydrological Systems • Fisheries • Agriculture (Production & Livestock) • Wildlife Ecosystems • FSR projects also address threats and hazards caused by or exacerbated by Climate Change including: • Climate Change Adaptation & Mitigation • Changing Weather Patterns & Severe Weather • Droughts and Floods Fluvial Geomorphology Branch of science concerned with influence of rivers and streams on the formation of the earth’s surface Governing Processes: • Erosion • Sediment Transport • Sediment Deposition Review of Basic Geomorphic Principles Natural Stream Systems Geomorphic Floodplain Terrace 1st Terrace Bankfull Width 2nd Terrace Bankfull Depth Review of Basic Geomorphic Principles Entrenched Channel Geomorphic Floodplain Bankfull Width Bankfull Depth Bankfull Discharge • Controls Channel Form • Corresponds to the Discharge at Which Channel Maintenance is Most Effective • Recurrence Interval on Order of 1.2 to 1.6 Years • Higher Recurrence Interval in Urban Watersheds Bankfull Indicators • Flat, Depositional Surface Adjacent to Active Channel • Height of Depositional Features (Point Bars) • Change in Vegetation • Slope or Topographic Breaks or Changes Along the Bank Review of Basic Geomorphic Principles Past Attempts at Designing Streams to Prevent Flooding Mini Los Angeles Flooded Skateboard River Dragstrip Half-Pipe Time-Released Bedload Capsules Review of Basic Geomorphic Principles Designing Channels to be Natural and Resilient Review of Basic Geomorphic Principles Designing Channels to be Natural and Resilient Review of Basic Geomorphic Principles Designing Channels to be Natural and Resilient Review of Basic Geomorphic Principles Differences CONCEPT TRADITIONAL GEOMORPHOLOGICAL Time Short-term Long-term Model Theoretical Field Measurement Water Clear Sediment Laden Spatial Scale Reach Watershed Boundary Rigid Mobile Maintenance High Sustainable Design Flow 100 yr. Bankfull Flow Factor of Safety Conservative Balance of Forces Natural Channel Design Overview Natural Channel Design Process by which new or re-constructed stream channels and their associated floodplain riparian systems are designed to be naturally functional, stable, healthy, productive, resilient to changing conditions, and sustainable. Natural Channel Design Overview Natural Channel Design Process • Determine Site Constraints & Design Parameters • Determine/Design Impact of Flood Flows on Potential Design • Predict Stable Geometry 1,100 ft Based on Reference Reach • Check Sediment Transport Competency and Capacity A • Iterative Design Until Geometry and Calculated Depths Converge Natural Channel Review Overview Primary Reference Chapter 11: Geomorphic Approach for Natural Stream Channel Design Restoration USDA NRCS, Stream Restoration Design Design Handbook, 2007. National Engineering Handbook Part 654 Released, August 2007 (vs. 031908) U.S. Department of Agriculture Natural Resources Conservation Service Natural Channel Design Overview Major Types of Restoration * Provide greatest potential • Priority I – Raise the Stream up to for reducing flood elevations the Floodplain • *Priority II – Excavate to Lower Floodplain and Create Storage along Newly Restore Channel with Stable Pattern and Profile • *Priority III – Does Not Alter Planform but Alters Cross-Section to Change Stream Type Along Existing Pattern • Priority IV – Armour in Place using Soil Bioengineering or More Structural Approaches Natural Channel Design Overview Reduction of Flood Elevation & Shear Stresses on Streams Degraded or γ Channelized Shear Stress = R S Stream 100-Year Storm D100 Natural/Restored D2 2-Year Storm Stream Shear Stress Degraded or Channelized Stream Discharge 100-Year Storm Return Interval D100 2-Year Storm D2 Naturally Stable or Restored Stream Vane & Grade Control Structures Use of Structures in Natural Channel Design • Provide Grade Control • Maintain Stable Aquatic Habitat • Maintain Shear Stresses for Sediment Transport • Decrease Bank Erosion • Fish Passage at All Flows • Control During Larger Flows • Diversion Structures • Bridge Openings to Protect Abutments Vane & Grade Control Structures Boulder Vane Riffle Vane & Grade Control Structures “Rock and Roll” Riffle Vane & Grade Control Structures Constructed Riffles Wbkf Vane & Grade Control Structures 1/3 1/3 1/3 Cross-Vane B C A D Approx. 20-30 Half Degrees Wbkf B C Cross Section View A A D B Flow Longitudinal Profile Wbkf Vane & Grade Control Structures 1/3 1/3 1/3 Double Step Cross-Vane B C A D Approx. 20-30 Half Degrees Wbkf B C Cross Section View A A D B Flow Longitudinal Profile Vane & Grade Control Structures Cross Vanes Vane & Grade Control Structures J-Hook 20-30 Vane Degrees Scour Pool Flow Cross Section View Vane & Grade Control Structures Log Vane with Sill Vane & Grade Control Structures J-Hook Vanes & Log Vanes/Root Wads Vane & Grade Control Structures Boulder Jam Step Pools Vane & Grade Control Structures Log Step Pools Vane & Grade Control Structures Step Pool Structures Floodplain & Habitat Features Wood Toe with Sod Mats Floodplain & Habitat Features Wood Toe with Sod Mats Floodplain & Habitat Features Oxbows Floodplain & Habitat Features Vernal or Ephemeral Pools Floodplain & Habitat Features Functions and Linkages Habitat for Amphibians & Invertebrates – Breeding – Rearing – Refuge Nutrient Processing – Organic Inputs – Hydric Soils Ecosystem Functions Flood Storage (Oxbows) Floodplain & Habitat Features Design Considerations Hydrology Ephemeral Pools Depth – Deep – Shallow Vegetation – In-pool – Shading Oxbow Old Outlet Channel Cut/Fill Balance Case Studies Case Studies Case Studies of Floodplain and Stream Restoration Projects Middle Fork of Beargrass Creek at Cherokee Park Stream Restoration, Louisville, KY Case Studies of Floodplain and Stream Restoration Projects Middle Fork of Beargrass Creek - Pre-Construction Conditions Exposed Utilities / Subsurface Utility Conflicts Over-Widened & Entrenched Channel Case Studies of Floodplain and Stream Restoration Projects Middle Fork of Beargrass Creek – During Construction Conditions Cross Vane Installation Floodplain Bench & Channel Grading Case Studies of Floodplain and Stream Restoration Projects Middle Fork of Beargrass Creek – Immediate As-Built Construction Minor Flood Flow Conditions Floodplain Bench & Narrowed Baseflow Channel Grading at Low Flows Case Studies of Floodplain and Stream Restoration Projects Middle Fork of Beargrass Creek – Year-One Post- Construction Normal Base Flow Conditions Functioning Cross Vane Case Studies of Floodplain and Stream Restoration Projects Middle Fork of Beargrass Creek – Post Out-of-Bank Flood Conditions Functioning Cross Vane at Receding Flood Conditions Out-of-Bank Rack Line Case Studies of Floodplain and Stream Restoration Projects Middle Fork of Beargrass Creek – Post Out-of-Bank Flood Conditions Receding Flood Conditions at Downstream Bridge Opening Receding Flood Conditions in Channel Case Studies of Floodplain and Stream Restoration Projects Middle Fork of Beargrass Creek – Post Out-of-Bank Flood Conditions Return to High Baseflow Conditions Case Studies of Floodplain and Stream Restoration Projects Katy Prairie Stream Restoration – Creation of Resilient Ecosystems Case Studies of Floodplain and Stream Restoration Projects Katy Prairie Stream Restoration Project Partners • Restoration Systems LLC • Warren Ranch • Katy Prairie Conservancy • Stantec • Forbes Consultancy • Land Mechanics • Wright Contracting • Stuckey’s Contract Services Summary • Umbrella Mitigation Bank • PRM for the Grand Parkway • 5 Phases • Phases 1 – 4 Constructed • 86,000 Total Feet • Post Construction Monitoring Project Background Case Studies of Floodplain and Stream Restoration Projects Katy Prairie Stream Restoration - Pre-Construction Conditions Case Studies of Floodplain and Stream Restoration Projects Katy Prairie Stream Restoration – During Construction Conditions Meander Bend Grading Channel Re-Grading Case Studies of Floodplain and Stream Restoration Projects Katy Prairie Stream Restoration – During Construction Conditions Toe Wood Installation Log Vane Installation Case Studies of Floodplain and Stream Restoration Projects
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