Rc201 day 1 jennings 10

Greg Jennings, PhD, PEProfessor, Biological & Agricultural EngineeringNorth Carolina State [email protected]

Stream Restoration

… 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

Streams are conduits in the water cycle and also important habitats

What is a Stream?

Photo Credit: Eve Brantley, Auburn University

• Communities of organisms and their physical, chemical, and biological environments

Streams are Ecosystems

What Makes a Stream Healthy?• Bed stability & diversity

• Sediment transport balance

• In-stream habitat & flow diversity

• Bank stability (native plant roots)

• Riparian buffer (streamside forest)

• Active floodplain

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

Sediment Transport Balance• Minor erosion & deposition

• Alluvial bars and benches

• Sufficient stream power to avoid aggradation

• No net change in sediment over long time

PoolRoots Wood

Leaf Pack

RiffleRocks

In-stream Habitat & Flow Diversity

Plants

Overhanging Bank

Bank Stability• Dense native

plant roots

• Low banks with low stress

Riparian Buffer (Streamside Forest)• Diverse native plants

• Food and shade

Active Floodplain• Regular (every year) flooding to relieve stress

• Riparian wetlands

• Stormwater retention & treatment

Why Restoration?

• Water quality impairments

• Habitat loss

• Ecosystem degradation

• Land loss

• Safety concerns

• Infrastructure damage

• Flooding

• Aesthetics

Stream Insults

• Straightening & dredging

• Floodplain filling

• Watershed manipulation

• Sedimentation & stormwater

• Pollution discharges

• Utilities & culverts

• Buffer removal

• Disdain & neglect

Activities that initiate or accelerate the recovery of ecosystem health, integrity, and sustainability (SER, 2004).

Ecosystem Restoration

1. design of an ecological river restoration project should be based on a specified guiding image of a more dynamic, healthy river

2. river’s ecological condition must be measurably improved

3. river system must be more self-sustaining and resilient to external perturbations so that only minimal follow-up maintenance is needed

4. during the construction phase, no lasting harm should be inflicted on the ecosystem

5. pre- and post-assessment must be completed and data made publicly available

Standards for ecologically successful river restoration

Palmer et al., Journal of Applied Ecology, 2005, 42, 208–217

Habitats

Water quality

Natural flow regimes

Recreation & aesthetics

Public acceptance

Outcomes of Ecosystem Restoration

Restoration Components

1. Channel morphology & floodplain connection

2. In-stream structures

3. Streambank bioengineering

4. Riparian buffers & habitat enhancements

5. Stream crossings

6. Stormwater/watershed management

7. Monitoring & maintenance

8. Public access & education

Healthy “reference”

streams serve as design templates

Natural Stream Channel Stability(from Leopold)

• River has a stable dimension, pattern and profile• Maintains channel features (riffles, pools, steps)• Does not aggrade (fills) or degrade (erodes)

• Dimension (bankfull & flood flow)• Pattern (meander)• Profile (bed profile)• Floodplain connection

1. Channel Morphology & Floodplain Connection

2005 NCSU Rocky Branch 2006

2008 NCSU Rocky Branch

Bankfull Stage: Water fills the active channel and begins to spread onto the floodplain

Stream Corridor Restoration: Principles, Processes, and Practices. 1998. Federal Interagency Stream Restoration Working Group.

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!

2008 Town Creek Tributary

Priority 1: Raise channel to existing valley and construct new meandering channel

2008 Purlear Creek 2009

2009 Purlear Creek

Priority 1

Priority 2

Priority 2: Excavate lower floodplain and construct new meandering channel

2008 Trib to Saugatchee Creek 2008

Wfpa

Wbkf

Entrenchment Ratio = Wfpa / Wbkf = 75/15 = 5

2007 Cary Walnut Creek Tributary 2008

Priority 2: Excavate lower floodplain and construct new meandering channel

Photo Credit: David Bidelspach, Stantec, Inc.

2008 Cary Walnut Creek Tributary

Priority 3: Excavate narrow floodplain benches in confined systems

2009 Little Shades Creek 2010

Wfpa

Wbkf

Entrenchment Ratio = Wfpa / Wbkf = 60/38 = 1.6

Before

After

Seoul, KoreaCheonggye“Extreme

Restoration”

Fac. of Environment & Life Sciences, Seoul Women's University

Before

After


Restoration process of Cheonggye stream


Typical cross-section of the restored stream section

Fac. of Environment & Life Sciences, Seoul Women's University Fac. of Environment & Life Sciences, Seoul Women's University

Stream Design Approaches

1. Threshold Channel

2. Alluvial Channel

a. Regime Equations

b. Analogy (Reference Reach)

c. Hydraulic Geometry

d. Analytical Models

3. Combination of Methods

Threshold Channels1. Rigid boundary systems

2. Simple design approach: select channel configuration where the stress applied during design conditions is below the allowable stress for the channel boundary

Threshold Channels

Shear Stress

Threshold Channels – Shear Stress

Shear Stress

= Rs

= Shear Stress (lb/ft2)

= Unit Weight of Water = 62.4 lb/ft3

R = Hydraulic Radius (ft) = A/P

s = Energy Slope (water surface) (ft/ft)

A = Riffle Cross-Section Area (ft2)

P = Wetted Perimeter (ft) [P ~ Wbkf + 2 x Dbkf]

http://www.epa.gov/warsss/sedsource/bedload.htm

http://www.epa.gov/warsss/sedsource/bedload.htm

Threshold Channels – Shear Stress

Shear Stress Around Bends

Shear Stress Distribution• Flow around bends

– creates secondary currents – higher shear stresses on the channel sides and bottom

compared to straight reaches – maximum shear stress in a bend is a function of the ratio of

channel curvature to bottom width

Shear Stress Distribution

from Chang, 1988

Shear Stress Distribution

Alluvial Channels1. Movable boundary systems

2. Complex design approach: assess sediment continuity and channel performance for a range of flows

3. Dependent variables: Width, Depth, Slope, Planform

4. Independent variables: Sediment inflow, Water inflow, Bank composition

5. Empirical & Analytical approaches should be used concurrently

Steady State Equilibrium

dimension, pattern and profile of the river and its velocity have adjusted to transmit the discharge and sediment load from its catchment under the present climate and land use conditions without any systematic erosion or deposition; namely regime conditions (Hey)

Assumption: Stream Behavior Is Predictable

• Streams evolve to a state of dynamic equilibrium

• Equilibrium is a function of flow and sediment

• Equilibrium is naturally associated with a main channel

and a flood-prone area

• The main channel is formed by the effective (“bankfull”)

discharge over time

• Alluvial stream meandering

is predictable

Design Criteria Selection

From Will Harman, Stream Mechanics

Alluvial Channels – Regime Approach1. Empirical equations

2. Use as a check

3. Hey equations:

Alluvial Channels – Analogy Approach1. Reference reach: Must have similar bed/bank materials,

sediment inflow, slope, valley type, and hydrograph

2. Upstream/downstream of design reach is best

3. Nearby similar watershed acceptable

4. Use as a starting point or check (BE CAREFUL)

Alluvial Channels – Hydraulic Geometry

1

10

100

1000

10000

0.1 1 10 100

Bank

full

Disch

arge

, Q (c

fs)

Drainage Area (sq mi)

Hydraulic Geometry Regional Curves

NC Piedmont

NC Mtn

MD Alleghany

MD

NY

VT

OH 01

OH 05

OK

SW OR

Pacific NW

AZ

AZ & NM

1

10

100

1000

0.1 1 10 100

Cros

s-se

ction

Are

a (sq

ft)

Drainage Area (sq mi)

Hydraulic Geometry Regional Curves

NC Piedmont

NC Mtn

MD Alleghany

MD

NY

VT

OH 01

OH 05

OK

SW OR

Pacific NW

AZ

AZ & NM

Hydraulic Geometry

National Center for Earth Dynamics

http://www.nced.umn.edu/Stream_Restoration_Toolbox.html

Single-Thread Gravel-Bed Rivers Have Consistent Bankfull Geometries

http://www.nced.umn.edu/Stream_Restoration_Toolbox.html

Alluvial Channels – Analytical Methods

1. Choose appropriate model

2. Assess a range of solutions

3. Use as a check

Analytical Design Approach, Shields, 2006

Combination Approach to Natural Channel Design

1. Existing Conditions – valley, watershed, constraints

2. Design Goals

3. Design Criteria

a. Regime Equations

b. Analogy (Reference Reach)

c. Hydraulic Geometry (Regional Curves)

d. Other Restoration Projects

4. Analytical Models

Natural Channel Design Approach, from Rosgen, 2006

Design Criteria Selection


Reference Reach Versus Design Reach

Reference reach with mature forest Stream restoration project immediately after construction; floodplain devoid of vegetation


Reference Reach Pattern


Reference Reach:

• Upstream/downstream• Same watershed• Similar watershed• Historical photos


Rc201 day 1 jennings 10

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