Stream Restoration: Working with Nature?

Transcription

1 Stream Restoration: Working with Nature? Greg Jennings, PhD, PE Ecosystem Restoration activities that initiate or accelerate the recovery of ecosystem health, integrity, and sustainability (SER, 2004) Why Restoration? Water quality impairments Habitat loss Ecosystem degradation Land loss Safety concerns Infrastructure damage Flooding Aesthetics 1

2 Stream Impairments Straightening & dredging Floodplain filling Watershed manipulation Sedimentation & stormwater Pollution discharges Utilities & culverts Buffer removal Disdain & neglect Outcomes of Ecosystem Restoration Habitats & water quality Natural flow regimes Recreation & aesthetics Public enthusiasm 2

3 Long Creek, Gaston Co ( ) Dairy Farm: Fencing, Bank Stabilization, Planting 10 years later Roaring River, Stone Mt State Park ( ) Trout Stream: Channel Realignment, Structures, Planting 10 years later Purlear Creek, Rendezvous Mt State Forest Trout Stream: Channel Realignment, Structures, Planting 3

4 Rocky Branch, NCSU Campus Urban Stream: Channel Realignment, Structures, Planting Planning a Stream Project: Goals? Stability, Habitat, Recreation? Constraints? Access, Land Availability, Utilities? Feasibility? Will it Work? Constructability? Equipment, Materials, Time/$? Stream Restoration Goals: What do people need, want, expect? Safe, abundant water Recreation Aesthetics Flood control Valuable land Healthy economy 4

5 Backyard Stream Repair Step 1: Grade Step 2: Rake Step 1: Grade Step 2: Rake Step 3: Seed Step 4: Straw Step 5: Trench Step 6: Mat Step 7: Stake Step 8: Plant 5

6 Step 1: Grade Step 2: Rake Step 3: Seed Step 4: Straw Step 5: Trench Step 6: Mat Step 7: Stake Step 8: Plant Temporary Matting Biodegradable (coir, jute, excelsior) Seed & straw UNDER mat Keep matting relaxed Trench in at top Wood stakes Step 1: Grade Step 2: Rake Step 3: Seed Step 4: Straw Step 5: Trench Step 6: Mat Step 7: Stake Step 8: Plant 6

7 Step 1: Grade Step 2: Rake Step 3: Seed Step 4: Straw Step 5: Trench Step 6: Mat Planting: ASK THE EXPERTS! Step 7: Stake Step 8: Plant September 2013 Case Study: Little Shades Creek Ashley Woods subdivision City of Vestavia Hills, AL Jefferson County Cahaba River Basin Drainage Area = 8 sq miles Impervious Surface = 35% 7

8 Need: Water Quality + Infrastructure Opportunity: Community Support + Technical Expertise + Administrative Persistence ADEM US Environmental Protection Agency City of Vestavia Hills Cawaco Resource Conservation & Development Council, Inc. Cahaba River Basin Clean Water Partnership Alabama Cooperative Extension System Ashley Woods Homeowners Association Project Partners The Nature Conservancy Alabama Department of Transportation North State Environmental North Carolina Cooperative Extension Goodwyn Mills & Cawood, Inc. Representatives Jabbo Waggoner, Greg Canfield, Jack Williams USDA/NRCS Morgan Properties 8

9 Project Goals Restore natural stream functions & services Reduce stormwater impacts to stream health Educate watershed stakeholders about stream health and stormwater management Project Specs 1,900 feet stream length feet riparian buffer 0.5 acre stormwater wetland 10 stormwater outfall channels Sewer crossing Greenway trail on East bank Gravel/cobble high bedload Project Components 1. Channel morphology 2. Floodplain structure 3. Hydrologic & hydraulic analysis 4. In-stream structures 5. Habitats & vegetation 6. Site & watershed conditions 7. Monitoring, maintenance, education 9

10 Priority 3: Excavate narrow floodplain benches in confined corridor ER = 1.6 W/d = 19 K = 1.2 R c /W = 2-3 Construction: Jan-Mar, 2010 How to Reduce Stream Erosion 1. Reduce flow velocity and depth: Floodplains to spread flow & reduce depth Roughness to slow velocity Vanes to re-direct flow from banks 2. Strengthen soil to resist erosion: Grading to stable slope to prevent slumping Temporary matting to cover soil Dense native plants for soil strength Entrenchment Ratio = W fpa / W bkf = 60/38 = 1.6 Width to depth Ratio = W bkf / d bkf = 38/2 = 19 10

11 Entrenchment Ratio = W fpa / W bkf = 60/38 = 1.6 In-Stream Structures (11): Boulder & Log Grade Control Bank Protection Sediment Transport Habitat Enhancement Boulder Vanes (J-hooks) 3-6 % arm slopes degree arm angles Boulder footers & non-woven geotextile 0.5 ft drops over j-hook inverts 11

12 Log Vanes 2-4 % arm slopes 20 degree arm angles Sealed with woven geotextile & backer logs Stormwater Outfall Channels (10) Vegetated bio-swales (low slope) Rock step-pools (high slope) Construction Practices Track equipment Spill management plan Staged construction phases to limit exposure 12

13 Temporary Erosion Control Soil prep, seed, straw Biodegradable matting (coir, 700g) Wood stakes Vegetation Streamside Forest Native plants Grasses, shrubs, trees Live stakes, bare roots, containers Stormwater Wetland Enhancement Runoff from 90 acres Sediment retention (78% reduction) Native plants nutrient cycling 13

14 Education & Engagement Signs Workshops: Construction, Planting, Maintenance Maintenance Planting Invasive plant removal Bank erosion brush mattress, coir logs Natural Succession July 2010 Partridge Pea, Chamaecrista fasciculata August

15 Is the Project Achieving Goals? Streambank erosion eliminated Floodplain & wetlands functioning Vegetation, water quality, & habitats improving Public understanding enhanced The Value of Demonstration: Shades Creek Samford University 1,000 ft enhancement 3 workshops Construction: January 2011 Shades Creek Enhancement: 2011 March 2011 September

16 More on Structures Correct morphology first Right structure in the right place Right equipment & materials for the job Plan for flood flows Multiple Log Vanes Saugahatchee Creek Multiple Log Vanes: Saugahatchee Creek Photo Credit: Dan Ballard, Town of Auburn 16

17 Offset Boulder Cross Vane at a Bridge Integrate Wood Wherever Possible Log J-hook Vane, Root Wads 17

18 Vanes, Toe Wood, Transplants Stream Restoration as a BMP Sediment control Nutrient cycling (instream & floodplain) Peak discharge attenuation Habitats (aquatic & terrestrial) Infrastructure protection Public Access & Education Greenways & paths Signs Tours & media Volunteers 18

19 Education & Engagement Signs Workshops: Construction, Planting, Maintenance Stream Restoration = Public Enthusiasm 19