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
Trang 1Riverbank Protection
CIVE 717 Assignment 4 Problem 2
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
Trang 2Vegetation
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
Grasses
REF: 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- 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
Trang 3Vegetation 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
REF: http://www.fws.gov/midwest/detroitriver/report_chapter2.html
Before & After planting grass on eroded
slope on Ottawa River, Ottawa Canada
Trang 4Vegetation - 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,
erosion-resistant material slides down and
protects bank as the figure
indicates.
Advantages
Very little design work needed
Easier to install on high banks
Disadvantages
Will lose more bank material until
intersects erosion-resistant material
Inconsistent results and steep side
slopes result in high velocity rivers
Conventional Windrow placement
Trench
Trench exposed and protecting bank
REF: Bottom two figures from Figure 8.8 in River Mechanics REF: Top figure from WES Streambank Handbook CIVE717 website
Trang 5 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
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
REF: www.wateronline.com/Content/ProductShowcase REF: http://www.incacape.co.za/landscaping.erosion.control.htm
Trang 6 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
Record of satisfactory performance
Disadvantages
Labor intensive
REF: www.ieca.org/photogallery/GabionIllustrations1.asp
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 6 months later
REF: www.ieca.org/photogallery/GabionIllustrations1.asp REF: www.ieca.org/photogallery/GabionIllustrations1.asp
Trang 7Articulated Concrete Mattresses
Used in large rivers (Mississippi)
Precast concrete blocks held together
by steel rods or cables
Advantages
Flexible, strong, and durable
Completely covers riverbank when properly placed
Can be placed quickly
Excellent service record
Disadvantages
~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
REF: Figure 8.11 in River Mechanics
REF: www.greenvillebridge.com/1a1_jan_02.htm
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
Trang 8Retaining 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
Trang 9Cantilever 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_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
Trang 10Retaining 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/commo ns/b/bd/Retaining_Walll_Type_Function.jpg
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