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Riverbank Protection

CIVE 717Assignment 4 Problem 2

Nathan Holste, Jon Renholds & Mick UrsicREF: http://project.jica.go.jp/laos/0245124E0/pdf/seminar_program_200603.pdf

Riverbank ProtectionPurpose - Usually defined as measures to strengthen the banks other than using riprapObjective - Show examples of many different types of riverbank protectionTypes

VegetationWindrows and TrenchesSacks and BlocksGabions and MattressesArticulated concrete mattressesSoil-CementRetaining WallsMany others possible

Sketches of different types of riverbank protection

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Vegetation -3 Main Types Trees

REF: http://www.hastings.nsw.gov.au/resources/images/McInherny-004.jpg

Application of native

Mangrove trees along

Hasting’s River (near

Sydney, Aust.)

Estuary along with rock toe

protection

Shrubs

GrassesREF: http://www.sotir.com/case_studies/study_wilmington_detail.html

Application of small shrubs along with terracing the slope in Wilmington, North Carolina

REF:www.vetiver.org/TVN_past_pict_gallery_htm

Application of vetiver grass for bridge protection in Queensland, Aust.

Vegetation Structure- FascinesBundles of cuttings tied togetherPlaced in shallow trenches parallel to the bankPartially buried and staked in place

Creates log-like structure that will quickly root, grow and provide plant coverHolds soil in place to protect streambank from erosion

REF: Streambank Revegetation and Protection: A Guide for Alaska

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Vegetation Planting MethodsLive Staking/Brush Mattress

Provides slope with protective vegetative coveringProvides erosion control with fish and wildlife habitatCreates good plant coverage and soil stabilityLabor intensive

REF: Stream Corridor Restoration: Principles, Processes, and Practices10/98 by FISRWG

Vegetation - Advantages

Least expensive of Riverbank Protection measuresImproves habitatAesthetically pleasing

REF: http://www.fws.gov/midwest/detroitriver/report_chapter2.html

Before & After planting grass on eroded slope on Ottawa River, Ottawa Canada

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Vegetation - DisadvantagesOn high banks tree roots may be not able to stabilize toe and weight of tree will cause bank failure when undercutMay be hard to grow in some areasMay suffer wildlife or livestock damageOnly certain plants can withstand conditions (wetting/drying, freeze/thaw, etc.)Shrubs can result in significant hydraulic resistance during flooding

Sketch of bank failure due to undercutting and the weight of large vegetation

Windrows and Trenches

Windrows involve piling sufficient supply of erosion-resistant material on bankTrenches are similar except they are buried to be less unsitelyWhen bank erodes further, erosion-resistant material slides down and protects bank as the figure indicates.Advantages

Very little design work neededEasier to install on high banks

DisadvantagesWill lose more bank material until intersects erosion-resistant materialInconsistent results and steep side slopes result in high velocity rivers

Conventional Windrow placement

Trench

Trench exposed and protecting bankREF: Bottom two figures from Figure 8.8 in River Mechanics

REF: Top figure from WES Streambank Handbook CIVE717 website

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SacksFilled with soil or sand-cement mixturePrimarily used for emergency work during floodsProtects streambanks when proper riprap isn’t availableAdvantages compared to stone riprap

Allow placement on steep slopesUse locally available materialsCreates smooth boundaryCobblestone effect may be more aesthetic

DisadvantagesHighly labor intensive (more costly)Susceptible to excess hydrostatic pressureUniformly sized – may require a filter materialVulnerable to environmental hazards

REF: Figure 8.9 in River Mechanics

Blocks

Manufactured with local materials or obtained commerciallyCast with openings to provide for drainage

Openings also allow vegetation to grow so that the root structure can strengthen the bank

Can be used with a filter if erosion is a concernAdvantages

Durable, less susceptible to freeze/thawEasy pedestrian access to riverLow channel boundary roughnessSufficient flexibility to conform to minor changes in bank shape

REF: www.wateronline.com/Content/ProductShowcase REF: http://www.incacape.co.za/landscaping.erosion.control.htm

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GabionsRectangular wire boxes (baskets) filled with small-sized stonesUsed where flow velocities are too high for riprap of small stonesMade of heavy galvanized steel with PVC coating for corrosive environmentsStacked on relatively steep slopes to resist river flows and unstable banksNeed to be periodically inspected and maintained from damageAdvantages

Record of satisfactory performanceDisadvantages

Labor intensiveExpensive REF: Ohio Stream Management Guide

REF: www.ieca.org/photogallery/GabionIllustrations1.asp

Mattress GabionsShaped into shallow, broad basketsTied together side by side to form continuous blanket of protectionPlaced on a smoothly graded riverbank slopeMay still allow some natural vegetation growth

Site under construction 6 months later

REF: www.ieca.org/photogallery/GabionIllustrations1.asp REF: www.ieca.org/photogallery/GabionIllustrations1.asp

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Articulated Concrete MattressesUsed in large rivers (Mississippi)Precast concrete blocks held together by steel rods or cablesAdvantages

Flexible, strong, and durableCompletely covers riverbank when properly placedCan be placed quicklyExcellent service record

Disadvantages~8% of surface area is open, allows fines to pass throughOpen spacing between blocks permits removal of bank materialDifficult to fit sharp curvesYearly inspection/maintenanceExpensive plant required for placement

REF: Figure 8.11 in River Mechanics

REF: www.greenvillebridge.com/1a1_jan_02.htm

Soil CementGood for arid

environments where freeze/thaw cycles are not likely to occur.

Works well with sandy soils where vegetation growth is difficult.

Has very little strength and is impermeable, both weaknesses may induce failure.

http://planning.co.la.ca.us/doc/case/TR53108_Vol5ApxB26_FinalTechMemoBuriedSoilCementEval.pdf

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Retaining Walls

Three distinct types:

1) Gravity Walls 2) Cantilever Walls 3) Sheet-Piling Walls

http://www.stormcon.com/ecm_0401_retaining.htmlhttp://www.menlopark.org/creek/MPSection4.pdfDas, Baja M. 2004. Foundation Engineering, Fifth EditionThomson Brooks Cole.

Gravity Walls

Crib Structure on South Platte

Gravity walls resist active and passive forces by the mass of the structure.

Gabions - Waterton Glacier International Peace Park 2007

Figure 8.13 – River Mechanics

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Cantilever Walls

Cantilever walls are used when there is a large amount of soil to be retained. The counterfort wall is an application that increases stability. These walls are typically made out of reinforced concrete. An anchor may also be used to increase stability.

Das, Baja M. 2004. Foundation Engineering: Fifth EditionThomson Brooks Cole.

http://www.humes.com.au/ctryimages/storage%20walls%20main.jpg

Sheet-Piling Walls

http://www.cmisheetpiling.com/img/bigwall.jpg http://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/Sheet_pile_New_Orleans-09-04-05.JPG/800px-Sheet_pile_New_Orleans-09-04-05.JPG

Advantages:

1) Easily installed

2) Highly effective

Disadvantages:

1) Limited height due to flexibility

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Retaining Wall Stability

4 typical modes of failure (Cantilever):

a) Overturning

b) Sliding

c) Bearing Capacity Failure

d) Deep-seated shear failure

Design concerns for all vertical structures include:

1) Earth Pressure

2) Hydrostatic Pressure (Groundwater)

3) Soil Type (Erosive Capability and Strength)

Das, Baja M. 2004. Foundation Engineering: Fifth Edition Thomson Brooks Cole.

http://upload.wikimedia.org/wikipedia/commons/b/bd/Retaining_Walll_Type_Function.jpg

ConclusionsMany other types of riverbank protectionOther river stabilization measures

include riprap and river control structuresMany times these are used together,

however riverbank protection is a very important part of overall river stabilization to protect life and property

One of many tools for Riverbank Protection -

EPA guidebook for Riverbank Protection

REF: http://www.mtwatercourse.org