jennings tdec stream small
TRANSCRIPT
Greg Jennings, PhD, PEProfessor, Biological & Agricultural EngineeringNorth Carolina State [email protected]
Understanding and Restoring Streams
… a body of water with a current, confined within a bed and streambanks
Synonyms: bayou, beck, branch, brook, burn, creek, crick, kill, lick, rill, river, rivulet, run, slough, syke
A stream is:• conduit in the water cycle• critical habitat• connected to a watershed
What is a Stream?
Fluvial Geomorphology:The study of landforms and fluvial processes
Fluvial processes are associated with flowing water, including sediment erosion, transport, deposition
Fluvial Forms• Bar• Channel• Confluence• Cutoff channel• Delta• Floodplain• Gorge• Gully• Meander• Oxbow lake• Pool• Riffle• Stream• Valley• Waterfall• Watershed
PoolRun
Point Bar (deposition)
Glide
Riffle
Meandering Stream: Alluvial Forms
Bankfull
Bankfull Stage“corresponds to the discharge at which channel maintenance is the most effective, that is, the discharge at which moving sediment, forming or removing bars, forming or changing bends and meanders, and generally doing work results in the average morphologic characteristics” (Dunne and Leopold,1978)
Stream Corridor Restoration: Principles, Processes, and Practices. 1998. Federal Interagency Stream Restoration Working Group.
• Channel (bed & banks)• Floodplain• Water & Sediment• Plants & Animals
Stream Ecosystems
Photo Credit: Eve Brantley, Auburn University
Stream Functions & Services1. Transport water
2. Transport sediment
3. Habitat (aquatic & terrestrial)
4. Recreation & aesthetics
5. Safe Water Supply
Effects of Urbanization on Streams (US EPA)
Urban Stream Syndrome (USS)• Response to watershed changes
• Loss of natural functions & values
• Causes problems locally & downstream
• Requires systematic assessment & treatment
Symptoms of USS
• Erosion & incision• Water quality decline• Habitat loss• Ecosystem degradation• Flooding• Land loss• Infrastructure damage• Recreation impaired• Aesthetics impaired• Economic loss
Urban Stream: Incision & bank erosion
Causes of USS• Watershed impervious• Channelization• Impoundments• Diversions• Floodplain filling• Pollution discharges• Sedimentation• Stormwater runoff• Utilities & culverts• Buffer loss• Neglect & Ignorance
University of Central Florida
Urban Disturbances to Hydrologic Cycle
Hydrograph Changes Due to Urbanization
0 20 40 60 800
10
20
30
40
50
Time (hours)
Stre
am F
low,
Q (
cfs)
Rural
UrbanHigher Peak FlowMore Runoff VolumeFlashier ResponseLower Baseflow
Runoff: more
Infiltration: less
Flooding: more
Baseflow: less
Constraints: Utilities, Road, Bridges, Culverts
What Makes a Stream Healthy?1. Bed stability & diversity
2. Sediment transport balance
3. In-stream habitat & flow diversity
4. Bank stability (native plant roots)
5. Riparian buffer (streamside forest)
6. Active floodplain
7. Healthy watershed
1. Bed Stability & Diversity• Appropriate size sediments to
resist shear stress
• Riffle/Pool sequences in alluvial streams
• Step/Pool sequences in high-gradient streams
Photo Credit: Eve Brantley, Auburn University
Riffles• Steep slope• High velocity & shear stress• Large substrate• High porosity & groundwater
exchange
Pools• Flat slope• Low velocity & shear stress• Small substrate• Scour during high flow
Problems: Bed Stability & Diversity• Headcut and excess scour
• Plane bed – filling of pools
• Armoring
2. Sediment Transport Balance• Minor erosion & deposition
• Alluvial bars and benches
• Sufficient stream power to avoid aggradation
Problems: Sediment Transport Balance• Excess stream power – eroding bed
• Insufficient stream power – aggradation
Streams convey water and sediment
Channel Evolution Model (Schumm, 1984)
Lane’s Balance (Lane, 1955)
Macrohabitats: riffles, runs, pools, glides, steps, side channels, scour holes
Microhabitats: roots, leaf packs, wood, rocks, plants, hyporheic zone
3. In-stream Habitat & Flow Diversity
Problems: In-stream Habitats• Uniform flow – lack of diversity
• Lack of wood, leaves, roots
• Water quality – DO, nutrients, toxics
4. Bank Stability• Dense native
plant roots
• Low banks with low stress
Problems: Bank Stability• Loss of vegetation
• High, steep banks – channelization
5. Riparian Buffer (Streamside Forest)• Diverse native plants
• Food and shade
Problems: Riparian Buffer• Mowers and moo’ers
• Invasive plants
• Armoring and impervious surfaces
6. Active Floodplain• Regular (every year) flooding to relieve stress
• Riparian wetlands
• Stormwater retention & treatment
Problems: Active Floodplain• Channel incision
• Floodplain fill and encroachment
7. Healthy Watershed• Stormwater management
• Wastewater management
• Upstream sediment control
Problems: Healthy Watershed• Stormwater energy and volume
• Point and nonpoint source pollution
• Erosion and sediment
Ecosystem Restoration:
“activities that initiate or accelerate the recovery of ecosystem health, integrity, and sustainability”(SER, 2004)
Planning a Stream Project:
• Goals? Stability, Habitat, Recreation?• Constraints? Access, Land Availability, Utilities?• Feasibility? Will it Work?• Constructability? Equipment, Materials, Time/$?
Case Study: Long Creek (1995-2005)• Dairy Farm: Fencing, Bank Stabilization, Planting
10 years later
Roaring River, Stone Mt State Park (2000-10)• Trout Stream: Channel Realignment, Structures, Planting
10 years later
Rocky Branch, NCSU Campus• Urban Stream: Channel Realignment, Structures, Planting
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
Restoration Components
1. Channel Morphology• Dimension (baseflow, bankfull, flood flows)
• Pattern (meandering, straight, braided)
• Profile (bedform – riffle, run, pool, glide, step)
2005 South Fork Mitchell River 2006
Photo Credits: Darrell Westmoreland, North State Environmental, Inc.
2011 South Fork Mitchell River
2011 South Fork Mitchell River
High-quality “reference” streams serve as design templates
Wbkf
dbkfAbkf
Bankfull Width, Wbkf = 9.3 ft; Bankfull Area, Abkf = 13.9 ft2
Mean Depth, dbkf = Abkf / Wbkf = 13.9 / 9.3 = 1.5 ft
Width to Depth Ratio, W/d = Wbkf / dbkf = 9.3 / 1.5 = 6.2
Morphologic Stream Classification Systems• Schumm (1977)
– Alluvial channels– Meandering, straight, braided– Type related to channel stability & sediment transport
• Montgomery & Buffington (1993)– Alluvial, colluvial, bedrock channels– Channel response related to sediment inputs– 6 classes of alluvial channels: cascade, step-pool,
plane-bed, riffle-pool, regime, and braided• Rosgen (1994)
www.wildlandhydrology.com
Rosgen Classification of Natural Rivers• Based on physical
characteristics (empirical)• Requires field
measurements• Requires bankfull
dimensions
www.wildlandhydrology.com
www.wildlandhydrology.com
G4 Eastern NC
2003
2000
2003
2001
2. Floodplain Structure• Regular (every year) flooding to relieve stress
• Floodwater retention & riparian wetlands
• Stormwater discharge retention & treatment
Entrenchment RatioER = Wfpa / Wbkf
Bankfull2 x dmbkf
above thalweg
Wfpa
Wbkf
dmbkf
Wfpa = Width of Flood Prone Area measured at the elevation twice bankfull max depth above thalwegWbkf = Width of Bankfull Channel
2006 Town Creek Tributary 2007
Priority 1: Raise channel to existing valley and construct new meandering channel
Rain will come during and immediately following construction!
ER = 15; W/d = 12
2008 Town Creek Tributary
Priority 1:lift channel
Incised Stream
Priority 2 & 3:lower floodplain
Stream Corridor Restoration: Principles, Processes, and Practices. 1998. Federal Interagency Stream Restoration Working Group.
Priority 2: Excavate lower floodplain and construct new meandering channel
2008 White Slough 2010
ER = 6; W/d = 11
White Slough 2010
Wfpa
Wbkf
Entrenchment Ratio = Wfpa / Wbkf = 90/15 = 6
Priority 2: Excavate lower floodplain and construct new meandering channel
2004 NCSU Rocky Branch 2005
Flood water flows onto floodplain several times each year
Wfpa
Wbkf
Rocky Branch Phase II Reach 2:Priority 2 (floodplain excavation, C channel)
Entrenchment Ratio = Wfpa / Wbkf = 90/20 = 4.5
2005 NCSU Rocky Branch 2006
Priority 3: Excavate narrow floodplain benches in confined systems
ER = 2.2; W/d = 12
Wfpa
Wbkf
Rocky Branch Phase II Reach 1:Priority 3 (floodplain excavation, Bc channel)Entrenchment Ratio = Wfpa / Wbkf = 40/20 = 2
2008 NCSU Rocky Branch
Priority 3: Excavate narrow floodplain benches in confined systems
2009 Little Shades Creek 2010
ER = 1.6; W/d = 15
Wfpa
Wbkf
Entrenchment Ratio = Wfpa / Wbkf = 60/38 = 1.6
Little Shades Creek 2010
In-Stream Structures (Logs & Rocks)• Streambank protection• Habitat enhancement (pools, aeration, cover)• Grade control• Sediment transport
Structure Criteria:• Natural materials• Habitats & passage for aquatic organisms• Natural sediment transport (alluvial systems)
Do you like these?
Boulder J-Hook Vane
Runaway Truck Ramp
Boulder J-Hook Vane• 3-5 % arm slopes
• 20-25 degree arm angles
• Boulder footers & non-woven geotextile
• 0.5 ft drops over j-hook inverts
Boulder Vane20-25 degree angles
3-5 % arm slopes
20-25 degrees
3-5 % arm slopes
Boulder
J-Hook Vane
Log Vane• 2-4 % arm slopes
• 20 degree arm angles
• Sealed with woven geotextile & backer logs
Log J-Hook Vane• Direct flow away from bank around bend• Grade control and scour pool• Brush toe buried under log vane• Backer logs & geotextile
Log J-Hook Vane• Hook boulders control grade• Footer boulders and geotextile• Boulder sills
Log J-Hook Vane• Hook boulders control grade• Footer boulders and geotextile• Boulder sills
Log J-Hook Vane
Multiple Log Vanes
Saugahatchee Creek
2007
2008
Multiple Log Vanes
Saugahatchee Creek
2009 January
2009 JulyPhoto Credit: Dan Ballard, Town of Auburn
Multiple Log Vanes: Saugahatchee Creek
2012 April Photo Credit: Dan Ballard, Town of Auburn
Boulder Cross Vane
Cross Vane• Direct flow in new channel alignment• Grade control and scour pool• Footer boulders & geotextile
• Undercut bed 2 ft and backfill with gravel, cobble, boulders, wood
• Cut thalweg 0.5 ft deep
Cross Vane (logs embedded)
Double-Drop Boulder Cross Vane
Photo Credit: Darrell Westmoreland, North State Environmental, Inc.
Double-Drop Boulder Cross Vane
Offset Boulder Cross Vane at a Bridge
Boulder W-Vane
Boulder Double Wing Deflector
Constructed Riffle
1st Order Streambed Transplant• Substrate transfer from old channel to new channel
Constructed Riffle• Undercut bed 2 ft and backfill with gravel, cobble,
boulders, wood• Cut thalweg 0.5 ft deep
• Undercut bed 2 ft and backfill with gravel, cobble, boulders, wood
• Cut thalweg 0.5 ft deep
Constructed Riffle
Riffles with Bouder/Log Steps
Wood• Food sources• Cover• Scour pools• Flow diversity
Brush Toe• Layers of logs and brush under water in pools• Live cuttings above water (silky dogwood, elderberry)• Matting, seed, transplanted alders on top
Brush Toe• Layers of logs and brush under water in pools• Live cuttings above water (silky dogwood, elderberry)• Matting, seed, transplanted alders on top
1. Plan for floods -- immediately & often
2. Plan for dry weather
3. Plan for vegetation maintenance
4. Understand constraints
5. Expect the Unexpected
Summary: Plan for Success