rock weir research overview 2006.10.17

8/11/2019 Rock Weir Research Overview 2006.10.17

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Rock Weir Design GuidelinesChris Holmquist-Johnson, MS, Bureau of ReclamationJoseph Mercure, BS, Colorado State University

David Mooney, MS, Bureau of Reclamation

http://www.usbr.gov/pmts/sediment/projects/RStructs


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Overview Research need and background Research components

Field Evaluation Physical Modeling 3D Numerical Simulations

Preliminary Results and Benefits Physical Model Details


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Background Rock weirs capabilities include: fish passage, bank protection,

channel profile stability, and improved aquatic habitat. Rock weirs are ideal structures for conditions ofsteep slopes,

bends, scalability, habitat, and aesthetics. Failures or loss of function can result in: disruption of service,

expensive repairs, maintenance cost, failure to meet biological and

geomorphic requirements, and loss of prestige. Initial laboratory results and qualitative field evaluations foundwidespread performance issues.

We think this is a flaw in the designs, not in the concept. The Rock Weir Design Guidelines Project was developed to

investigate failure mechanisms and provide methods for designingsustainable structures.


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Research ComponentsThe Rock Weir Research Project takes a multifaceted

approach incorporating mutually supporting field,laboratory, and numerical studies.

Field

Laboratory Computer

Provides acontrolledsetting

Includesscourprocesses

Physicallyreplicateshydraulics

Inexpensivelysimulateslarge numbersof cases

Increasesrange ofapplicability

Provides adesign tool

Evaluates current methods Hypothesizes successful techniques

Identifies failure mechanisms Creates a practical link


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Evaluation of Field Performance Field evaluation collected information

on many different design methodsaround the western United States.

Field evaluations identified severalfailure mechanisms. Scour and Slumping Flanking Loss of Pool Depth Incipient Motion

Identifying failure pathways allowsdesign of countermeasures.

Field measurements provide apractical link to guide and validatelaboratory and numericalinvestigations.


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Laboratory Physical Modeling Field investigation identified growth of a scour hole causing

geotechnical movement as the primary failure mechanism forrock weirs.

Understanding the scour processes and quantities provides vitalinformation on failure modes and potential counter measuresrequired to design sustainable structures.

Understanding failure modes in the field is COMPLICATED. Analyzing scour hole development is best answered in a

controlled environment such as the laboratory. Benefits include

Scour prediction method Potential counter measures and retrofits Rating curves for flood elevations Low flow depths and velocities for passage criteria


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Need and Benefits of Numerical Modeling Field and laboratory provide data over a limited range of conditions. Narrower ranges of conditions limit the applicability of results. Numerical modeling provides opportunity to test numerous design

parameters over large ranges for less money and in a shorteramount of time to extend the applicability.

The complex flow patterns require 3-dimensional simulations .Velocit y VectorsParallel to Bed

Velocity Vector sReturning Parallel

to Bed

Plunging Flow

Hydraulic Jump

Rapid VerticalContraction and

Expansion over theWeir Crest


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Physical Model Testing includes:

Average river geometries.

Mobile boundary. Fine gravel, medium gravel, and

very coarse gravel.

Data collection includes: Topographic bed surveys, 3D velocities, and Water surface data.

Results will assist indeveloping a scour predictionmethod.


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Physical Model Results

Theoretical

Physical Model(Q bankfull , Small cobble )

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Difference in scour hole definitionbetween theoretical and physical model

Max scour


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Physical Model Shakedown Results

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Drop Ht = 0 ft

Difference in scour hole definition between installing the throat crest:with no drop (level with the bed) vs. with a drop

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Drop Ht = 0.14 ft


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Physical Model ResultsScour Hole Evolution (15mm bed)1/3 Q Bankfull - two separate scour holes located near the arms2/3 Q bankfull - scour holes enlarge and move together Q bankfull - one large scour hole located below the throat

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1/3 Q Bankfull 2/3 Q Bankfull QBankfull


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Research Summary

The research produces tools and guidelines for structuredesign or retrofits based upon predictable engineeringand hydraulic performance criteria.

Understanding the processes governing success andfailure allow designers to construct robust andsustainable structures requiring fewer repairs, lessdisruption of service, and lower maintenance costs.

Guidelines simplify and reduce future design effortswhile increasing the likelihood of successful structures.

We hope that solidly developed criteria will simplify theregulatory permitting processes.


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In the End Reliable structure designs reduce failures,

Fewer retrofits saves money,

Reduced failures results in fewer retrofits,

Saving money while meetingregulatory requirements governinghabitat and fish passage makeseveryone happy

rock weir research overview 2006.10.17

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