natural channel design, bk p dbank processes, and

Natural Channel Design, B k P dBank Processes, and

Potential Performance Standards

1Prepared by U.S. EPA for 9/20/12 technical discussions with MA, CT and General Electric

d i d b ll

Natural Channel DesignNatural Channel Design

Process by which new or re-constructed stream channels and their associated flood-plain riparian systems are designed to be naturally functional, stable, healthy, productive and sustainableproductive and sustainable.


River Stability River stability (equilibrium or quasi-equilibrium) is defined as,

y

“the ability of a river, over time, in the present climate to transport the flows and sediment produced by its watershed in such a manner that the stream maintains its dimension, pattern and profilep p without either aggrading or degrading” (Rosgen, 1994)

33 Prepared by U.S. EPA for 9/20/12 technical discussions with MA, CT and General Electric

( ti )

River Components

• Channel Dimension (cross-section)

44 Source: Stream Corridor Restoration: Principles, Processes, and Practices; October 1998

Prepared by U.S. EPA for 9/20/12 technical discussions with MA, CT and General Electric

River Components • Channel Dimension (cross-section) • Meander Pattern (plan form)

55

Straightened Walla Walla River in Washington Returns to Meandering Stream During Major Flooding – Source: Wildland Hydrology.


RR

River Components

Ch l Di i RiffleRiffle PoolPool• Channel Dimension (cross-section)

RiffleRiffle PoolPool

GlideGlideRunRun )

• Meander Pattern (plan form)

• Channel Profile

RiffleRiffle

66PoolPool

RunRun GlideGlide


River Components

• Meander Pattern (plan f )form)

• Channel Dimension (cross(cross-section)

• Channel Profile

River that is disconnected from its floodplain results in increased shear stress and mass bank wasting

• Floodplain Connectivityy (really a component of Dimension) River with good floodplain connection

typically has stable banks and good

77

habitat


Example - Planform Indicators of Instability

• Meander Wavelength (Lm)/Riffle Bankfull Width (Wbkf) • Radius of Curvature (Rc)/Riffle Bankfull Width (Wbkf) • Beltwidth (Wblt)/Riffle Bankfull Width (Wbkf) = MWR • Pool to Pool Spacing/Riffle Bankfull Width (Wbkf) • Sinuosity = Channel Length/Valley Length


vature

/ f 2 4

C ff

Planform Indicators of Instability

Example - Radius of CurCurvature

• Reference Ranges of Rc/Wbkf = 2 to 4

• Erosion Initiated at Values < 2.5

• Severe Erosion Tends to Develop on Lower 1/3 of BendBend

• Lateral Migration • Formation of Chute

99

Cutoffs


1886 2006 @ N L R d1886 2006 @ WWTP

Housatonic RiverHousatonic River

River Changes

1010

1886 - 2006 @ New Lenox Road1886 - 2006 @ WWTP


Housatonic River Instability

On-going adjustments are occurring in the Rest of River

Contaminated bankContaminated bank erosion in 5A and 5B accounts for ~45%accounts for 45% of PCBs currently entering the river


Housatonic RiverHousatonic River

Channel Widening – Bank Erosion

Source: Stream Corridor Restoration:Source: Stream Corridor Restoration: Principles, Processes, and Practices; October 1998

1212

Bank Erosion - High Terrace


Housatonic RiverHousatonic River Horizontal Migration – Bank Erosion & AggradationAggradation

Source: Stream Corridor Restoration: Principles, Processes, and Practices; October 1998

1313 Bank Erosion - Floodplain Deposition


Bank Erosion Bank erosion is caused when the force applied to the bank exceeds the ability of the bank to resist deformationdeformation

Elkhead Creek Colorado

1414 Housatonic River – Reach 5A


g

y

BANCS Model

• Bank erosion prediction for the Rest of River Solids loadings

• Bank Erosion Hazard Index (BEHI)

• Near-Bank Stress (NBS)

• Developed as part of EPA’s WARSSS – Watershed Assessment for River Stability and Sediment Supply


!Process to d'etermine the Bank Erosio1111 lfaz:ard lnde.x.IBEHij·

-- - -Meas•ne Mi!:asure MYsure lllankfll l Root Root Helg1lt Depth IDeliSi\y

(8) CDI (f)

Mefiure Ml'aswre lhunlt Surfll;ee

,MI. DIA Fl<[DIA!· Angle Protection ~ i'll

Bank Erosion Hazard Index (BEHI)

BEHI Matrix

Prepared by U.S. EPA for 9/20/12 technical discussions with MA, CT and General Electric 1616

R t D it

BEHI Variables

Study Bank Height / Bankfull Height (C)

3

3.5

heig

ht /

eigh

t

Root Depth / Study Bank Height (E)

0.7 0.8 0.9

1

/ ban

k t• Bank Height

1

1.5

2

2.5

0 2 4 6 8 10

BEHI rating

Stu

dyba

nkh

bank

full

he

Very Low

Low

Mod

High 9

Extrem

e

Very

High

0 0.1 0.2 0.3 0.4 0.5 0.6

0 2 4 6 8 10

BEHI rating

Roo

t dep

th/

heig

ht

Very Low

Low

Mod

High

Very H

igh

9

Extrem

e

• Bank Height • Root Depth

Weighted Root Density (G)

0

20

40

60

80

100

Wei

ghte

d ro

otde

nsity

%

Bank Angle (H)

0

20

40

60

80

100

120

Deg

rees

• Root Density • Surface Protection

0 0 2 4 6 8 10

BEHI rating

VeryL

ow

Low

Mod

High

Very H

igh

9 Extrem

e

0 0 2 4 6 8 10

BEHI rating

Very

Low

Low

Mod

High

Very H

igh

9

Extrem

e

Surface Protection (I)

80

100

nt

• Bank Angle • Bank Material

0

20

40

60

0 2 4 6 8 10

BEHI rating

Perc

en

VeryL

ow

Low

Mod

High

VeryH

igh

9

Extrem

e

• Stratification


ver

Bank Erosion Hazard Index (BEHI)

BEHI = Very High Housatonic River

BEHI = Low Housatonic Ri

1818

Housatonic River


As summarized in Stantec 2009

• Force Exerted on the Stream Bank in the Near Bank Region (Near Bank 1/3 Width)Bank Region (Near Bank 1/3 Width)

• Various Methods to Determine NBS


Housatonic River Reach 5A

2020

Wiemenuch Creek, CO


Housatonic River Reach 5A

2121

Wiemenuch Creek, CO


para

Rest of River Bank Erosion and Meander Study

• Performed for use in the conceptual model and EFDC meterizationparameterization

• Comparison of aerial photos 19521952 1972 1990 2001

• Focused on movement on outside meander bends

• Short-term Erosion Study 15 Sites Surveyed (Nov. 2001 – June 2002)


Aerial Imagery 1952 - 2001


Short–term Erosion Study

Site ER-10: Example of woody debris deflecting flow into the bank causing erosion.

24

Site ER-9: Example of Bank slumping erosion.


Reach 5AReach 5A Estimate of one-third of banks derived from:

• Assumptions made for EFDC modeling based on Assumptions made for EFDC modeling based on Short-term Bank Erosion Study

• Preliminary BEHI estimates (Stantec 2009)


High Very High

High Mod

High

-- Mod High •••••••••••••••••• -- Mod

-- Mod Low

--- Low

-- Low Mod

-- very Low

-- Very Low Low

W 1 ppm Boundary

0 River/Ponds


Reach 5A Sediment removal and subsequent capping shall

result in a final grade consistent with the original grade or with modifications as needed considering Natural Channel Design considering Natural Channel Design …


- -

Consider the three river components, e.g.:Consider the three river components, e.g.: • Reduce severe radius of curvatures to lower the likelihood of

future chute cutoffs • Construct channel cross-section and profile to reduce near-• Construct channel cross section and profile to reduce near

bank sheer stress • Reconnect high flow channel to floodplain


Example

Example: Planform Instability – Tight Radius of CurvatureRadius of Curvature

2929

Bank Erosion – Lower 1/3 of Meander Bend


co ta s 5 o eate o t C s

d

Reach 5AReach 5A Remove contaminated soil from eroding banks …

locations shall be determined using a BANCSlocations shall be determined using a BANCS model calibrated for the Housatonic River and the collection of additional riverbank soil PCB data. • A bank shall be considered contaminated if it

contains 5 mg/kg or greater of tPCBs …g/ g g • A bank shall be considered to be erodible if its BEHI

and NBS is classified as Moderate-High or greater …


EXTREME BEHI BER = 0.0642e0.9391NBS

10

Site-specific validation is needed

11

n R

ate

(BER

) in

ft / y

r

MODERATE BEHI BER = 0.0556e0.5057(NBS)

HIGH & VERY HIGH BEHI

BER = 0.109e0.4159(NBS)

0.1Ban

k Er

osio

n

LOW BEHI BER = 0.0082e0.7349(NBS)

3131

Low Moderate High ExtremeVery Low Very High0.01 0 1 2 3 4 5 6 7

Near-Bank Stress (NBS)


v r ve econstr to

q ;

Reach 5A Exca ated i rbanks shall be r uctedExcavated riverbanks shall be reconstructed to

minimize erosion considering the principles of Natural Channel Design … This will allow the maximum use of bioengineering methods in restoring riverbanks. Riverbank reconstruction shall follow a hierarchy ofyapproaches as follows:

a) Reconstruct disturbed banks with bioengineering restoration techniques;

b) Reconstruct disturbed banks with a cap layer extending into the riverbank placed under a bioengineering layer; or,

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c) Place riprap layer or hard armoring on surface of banks (e.g. where needed for protection of adjacent infrastructure).


Bioengineering

The use of living and non-living materials to provide soil reinforcement and prevent erosion


Example - Channel Dimension and Bioengineering Reducing Near Bank Shear StressBioengineering Reducing Near-Bank Shear Stress

34

Source: Wildland Hydrology


t t

Example -St R d N B k Sh StStructures to Reduce Near-Bank Sheer Stress

3535

Source: Wildland Hydrology


Example – Cap in River With Bioengineering on BanksWith Bioengineering on Banks


Example – Cap with Overlying BioengineeringOverlying Bioengineering


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Questions?


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