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Fluvial Geomorphological-

Based EngineeringSolutions for the UpperMississippi River

Presented to:

PIANC USA Annual Meeting 2010

September, 2010Boston, Massachusetts

Lee W. Forbes, PE, D.WREGulf Coast Program Manager

[email protected]

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Stable Streams The New Design Goal

A stable stream moves thesediment and water generated byits watershed while maintaining

dimension, pattern and profile,without aggrading or degrading

The New Design Goal

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Natural Channel Design & Stream Restoration

Attempts to restore

impaired streams to astate of natural channel

stability, or dynamic

equilibrium, through the

understanding of fluvial

geomorphology and its

application via hydraulic

design methodologies.

Photo courtesy of Stantec

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Dynamic EquilibriumThe entropic tendency

of river systems towardminimum total work

and uniform work rate

in response to the

natural variations ofwater and sediment

loads to the system.

The Lane Relationship forStable Channel Balance

Q Sed x D 50 S x Q Water

Image courtesy of Wildland Hydrology

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Fluvial Geomorphology

The science of the formationof riverbeds, flood plains, andstream forms by the action ofwater.

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Optimized Natural Channel Forms

Dynamic Equilibrium Balanced through 4 Dimensions

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Optimized Natural Channel Forms

Lateral (Planform) Dynamic Equilibrium

Sine-Generated Curve Path of Minimum Bending Stress Path of Minimal Directional Variance Path that represents the the Most Likely Random Walk

Heading Angle = csin(s)

s = Distance Downriver (radians)

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Optimized Natural Channel Forms

Longitudinal Vertical Dynamic Equilibrium

Image courtesy of Wildland Hydrology

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Optimized Natural Channel Forms

Cross-Sectional & Temporal Dynamic Equilibrium

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The Stream Form Continuum

Images courtesy of Wildland Hydrology

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PROBLEM: Channel Response to Past andCurrent Hydromodification

Photos courtesy of NRCS

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PROBLEM: Channel Evolution in Response toHydromodification

Simons (1989) model of channel response in disturbed alluvial channels

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Dont Natural Streams have Unstable Banks?

Wolf Creek Case Study

Sediment Unstable Reach 80 x Sediment Stable Reach

Although streambankerosion is a naturalprocess, anthropogenicchanges (flow alteration),

such as urbanizationand channelization,destabilize streams causingdrastically acceleratedchannel erosion.

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Upland/Hillslope vs. In-Channel Sediment LoadsSediment from stream channels account for as much as 85% of watershed sedimentyields, and streambank retreat rates as high as 7.26 m/yr have been documented(Simon, A. et al, 2000)

~ 631,000 metric tons eroded duringseven months, or approximately:

X 42,000

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Design Approaches to Stream Restoration

Analytical Approach:

Based on numericalanalysis of physical,hydrodynamic processesthrough the system viaengineeringmethodologies such as

hydraulics and sedimenttransport theory

Juvenile, highly complex science being developed by many

different disciplines (engineers, life scientists, geologists, etc.)Challenges: As many as 15 independent and dependent

variables Only 3 suites of equations available

Continuity Equation Flow Resistance Equations Sediment Transport Equations

Currently, there are more independentvariables than we have physical process-based equations to solve

Must rely on values for variables derived bynon-analytical (analog and empirical) means

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Design Approaches to Stream Restoration

Analog Approach:Adopts templates from historic or adjacentchannel characteristics and assumes equilibriumbetween channel form and sediment andhydrologic inputs (aka Carbon Copy, or Reference

Reach Approach)Challenges: Requires a stable Reference Reachwith identical boundary conditions to ProjectReachrarely possible in urbanized settings

Michigan Thumb-Eastern Coastal Regional Curve

y = 1.4604x 0.1858

R2 = 0.5945

y = 12.302x 0.5128

R2 = 0.8169

y = 13.123x 0.3087

R2 = 0.7813

0.1

1

10

100

1000

0.1 1.0 10.0 100.0 1000.0

Watershed Area (sq. mi.)

C h a n n e

l D i m e n s

i o n

( f t ) o r

C h a n n e

l A r e a

( s q .

f t . )

BKF XS Area, sq ft

BKF Width, ft

BKF Depth, ft

Power (BKF Depth, ft)

Power (BKF XS Area, sq ft)

Power (BKF Width, ft)

Empirical Approach:

Uses equations that relate various channelcharacteristics derived from regionalizedor universal data sets (aka RegionalCurve Approach)

hoto courtesy of Stantec

Challenges:Regionalrelationships are notsufficient or specific enoughto develop complete designs

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Design Approaches to Stream Restoration

Best Design Solution:Practical, functional design requires the appropriate application ofelements of three design approaches and frequent design checksfrom across methodologies (i.e., analytical, empirical, and analog)

BRING A BIG TOOLBOXAND KNOW HOW TO USEALL OF YOUR TOOLS

Analog Solutions

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Solutions for the Upper Mississippi River

TributaryStreamRestoration

Photo courtesy of Stantec

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Solutions for the Upper Mississippi River

WetlandRestoration

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Solutions for the Upper Mississippi River

SetbackLevees

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Solutions for the Upper Mississippi River

Small DamRemoval &FishPassages

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Solutions for the Upper Mississippi River

IslandRestoration

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Solutions for the Upper Mississippi River

Slough &BackwaterRestoration

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Solutions for the Upper Mississippi River

StrategicDredging(Pools) ofLarge

Channels

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Solutions for the Upper Mississippi River

StreambankStabilization