Purpose Usually defined as measures to strengthen the banks other than using riprap Objective Show examples of many different types of riverbank protection Types Vegetation Windrows and Trenches Sacks and Blocks Gabions and Mattresses Articulated concrete mattresses SoilCement Retaining Walls Many others possible
Riverbank Protection CIVE 717 Assignment Problem Nathan Holste, Jon Renholds & Mick Ursic REF: http://project.jica.go.jp/laos/0245124E0/pdf/seminar_program_200603.pdf Riverbank Protection Purpose - Usually defined as measures to strengthen the banks other than using riprap Objective - Show examples of many different types of riverbank protection Types Vegetation Windrows and Trenches Sacks and Blocks Gabions and Mattresses Articulated concrete mattresses Soil-Cement Retaining Walls Many others possible Sketches of different types of riverbank protection Vegetation Main Types Shrubs Trees Application of native Mangrove trees along Hasting’s River (near Sydney, Aust.) Estuary along with rock toe protection REF: http://www.hastings.nsw.gov.au/resources/images/McInherny-004.jpg Application of small shrubs along with terracing the slope in Wilmington, North Carolina REF: http://www.sotir.com/case_studies/study_wilmington_detail.html Grasses Application of vetiver grass for bridge protection in Queensland, Aust REF:www.vetiver.org/TVN_past_pict_gallery_htm Vegetation Structure- Fascines Bundles of cuttings tied together Placed in shallow trenches parallel to the bank Partially buried and staked in place Creates log-like structure that will quickly root, grow and provide plant cover Holds soil in place to protect streambank from erosion REF: Streambank Revegetation and Protection: A Guide for Alaska Vegetation Planting Methods Live Staking/Brush Mattress Provides slope with protective vegetative covering Provides erosion control with fish and wildlife habitat Creates good plant coverage and soil stability Labor intensive REF: Stream Corridor Restoration: Principles, Processes, and Practices 10/98 by FISRWG Vegetation - Advantages Least expensive of Riverbank Protection measures Improves habitat Aesthetically pleasing Before & After planting grass on eroded slope on Ottawa River, Ottawa Canada REF: http://www.fws.gov/midwest/detroitriver/report_chapter2.html Vegetation - Disadvantages On high banks tree roots may be not able to stabilize toe and weight of tree will cause bank failure when undercut May be hard to grow in some areas May suffer wildlife or livestock damage Only 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 bank Trenches are similar except they are buried to be less unsitely When bank erodes further, erosionresistant material slides down and protects bank as the figure indicates Advantages Very little design work needed Easier to install on high banks Conventional Windrow placement REF: Top figure from WES Streambank Handbook CIVE717 website Trench Disadvantages Will lose more bank material until intersects erosion-resistant material Inconsistent results and steep side slopes result in high velocity rivers Trench exposed and protecting bank REF: Bottom two figures from Figure 8.8 in River Mechanics Sacks Filled with soil or sand-cement mixture Primarily used for emergency work during floods Protects streambanks when proper riprap isn’t available Advantages compared to stone riprap Allow placement on steep slopes Use locally available materials Creates smooth boundary Cobblestone effect may be more aesthetic Disadvantages Highly labor intensive (more costly) Susceptible to excess hydrostatic pressure Uniformly sized – may require a filter material Vulnerable to environmental hazards REF: Figure 8.9 in River Mechanics Blocks REF: www.wateronline.com/Content/ProductShowcase REF: http://www.incacape.co.za/landscaping.erosion.control.htm Manufactured with local materials or obtained commercially Cast 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 concern Advantages Durable, less susceptible to freeze/thaw Easy pedestrian access to river Low channel boundary roughness Sufficient flexibility to conform to minor changes in bank shape Gabions Rectangular wire boxes (baskets) filled with small-sized stones Used where flow velocities are too high for riprap of small stones Made of heavy galvanized steel with PVC coating for corrosive environments Stacked on relatively steep slopes to resist river flows and unstable banks Need to be periodically inspected and maintained from damage Advantages REF: www.ieca.org/photogallery/GabionIllustrations1.asp Record of satisfactory performance Disadvantages Labor intensive Expensive REF: Ohio Stream Management Guide Mattress Gabions Shaped into shallow, broad baskets Tied together side by side to form continuous blanket of protection Placed on a smoothly graded riverbank slope May still allow some natural vegetation growth Site under construction months later REF: www.ieca.org/photogallery/GabionIllustrations1.asp REF: www.ieca.org/photogallery/GabionIllustrations1.asp Articulated Concrete Mattresses Used in large rivers (Mississippi) Precast concrete blocks held together by steel rods or cables Advantages REF: Figure 8.11 in River Mechanics Flexible, strong, and durable Completely covers riverbank when properly placed Can be placed quickly Excellent service record Disadvantages REF: www.greenvillebridge.com/1a1_jan_02.htm ~8% of surface area is open, allows fines to pass through Open spacing between blocks permits removal of bank material Difficult to fit sharp curves Yearly inspection/maintenance Expensive plant required for placement Soil Cement Good 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 Retaining Walls Three distinct types: 1) Gravity Walls 2) Cantilever Walls 3) Sheet-Piling Walls http://www.stormcon.com/ecm_0401_retaining.html http://www.menlopark.org/creek/MPSection4.pdf Das, Baja M 2004 Foundation Engineering, Fifth Edition Thomson 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 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 Edition Thomson 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_Orle ans-09-04-05.JPG/800px-Sheet_pile_New_Orleans-09-04-05.JPG Advantages: Disadvantages: 1) Easily installed 1) Limited height due to flexibility 2) Highly effective Retaining Wall Stability Design concerns for all vertical structures include: 1) Earth Pressure 2) Hydrostatic Pressure (Groundwater) 3) Soil Type (Erosive Capability and Strength) http://upload.wikimedia.org/wikipedia/commo ns/b/bd/Retaining_Walll_Type_Function.jpg typical modes of failure (Cantilever): a) Overturning b) Sliding c) Bearing Capacity Failure d) Deep-seated shear failure Das, Baja M 2004 Foundation Engineering: Fifth Edition Thomson Brooks Cole Conclusions Many other types of riverbank protection Other river stabilization measures include riprap and river control structures Many 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 10 ... Many other types of riverbank protection Other river stabilization measures include riprap and river control structures Many times these are used together, however riverbank protection is a very... 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... of Riverbank Protection measures Improves habitat Aesthetically pleasing Before & After planting grass on eroded slope on Ottawa River, Ottawa Canada REF: http://www.fws.gov/midwest/detroitriver/report_chapter2.html