02_scour and protection

8/13/2019 02_Scour and Protection

1/46

Scour and scour protection

Krystian W. Pilarczyk

Rijkswaterstaat

Road and Hydraulic Engineering Division,

Delft, the Netherlands


2/46

Types of scour

Currents

Jets

Waves


3/46

Types of scour

a) S2 = S1 > 0. This is a dynamic equilibrium situation.

Sediment can be picked up and can settle again, but there is

no net change of the position of the bottom.

b) S2 > S1 = 0. There is no sediment supply from upstream,

while there is sediment transport downstream. This case isknown as clear-water scour. (uo1< uc)

c) S2 > S1 > 0. There is sediment supply from upstream but the

sediment transport downstream is larger. This case is known

as live-bed scour. (uo1> uc)

S f S f c

( ) ( ) or

Types of scour

Or, S = f(uuc)


4/46


5/46

Flow deflectors

Increase footing depth

Examples scour damage


6/46

Literature

See also selected literature in lectures by Pilarczyk


7/46


8/46

General aspects

and components

Hydraulic boundaryconditions

-flow pattern

- soil conditions


9/46

scour behind bed protection

4.07.0

2.0

0

7.1

10)( thuuth cs

hs(t) maximum scour depth

h0 original water depth

u vertically averaged velocity at end of protection

uc critical velocity

t time in hours scour intensity parameter


10/46


11/46


12/46


13/46


14/46


15/46


16/46


17/46

Bank sliding Zeeland

Probably due to flow slide

schematic view of a flow-slide

l d fi i i fi b d


18/46

Control definitions of

scour depth?

Sometimes = scour depth

Sometimes = scour depthplus water depth

Scour Manual, 1997

Hoffmans&Verheij

Scour in bends


19/46

River, Coastal and Shoreline Protection: Erosion

Control Using Riprap and ArmourstoneC. R. Thorne (Editor), Steven R. Abt (Editor), Frans B. J. Barends

(Editor), Stephen T. Maynord (Editor), Krystian W. Pilarczyk (Editor)Hardcover , 784 pages , April 1995

Velocity prediction in bendsempirical method

Vtoe/Vavg= 1.660.42 log (Rc/w)

(Rc/w)= the radius of river curvature to widthratio for the bend

WES (US Army):

Vtoe/Vavg= 1.750.5 log (Rc/w)


20/46

Bend scour depth prediction-empirical method

(Thorne, 1988, 1995)

All meanders:

dmax/dbar= 2.070.19 log (Rc/w-2)

Revetted bends:

dmax/dbar= 2.150.27 log (Rc/w-2)

Equation for the prediction of maximum bend scour

(dmax) on the basis of the mean depth of the

approach channel at the crossing upstream of thebend (dbar) and the bend geometry represented by

the ratio of bend radius (Rc) divided by width at the

upstream crossing (w).


21/46


22/46

Comment Steve Maynord

Regarding bend scour, dmax and hb are the maximum water depth inthe bend, not scour depth. Dbar and h are the average or hydraulic

depth in the channel approaching the bend. I prefer using a form ofthese equations I published in:

Maynord, S.T. (1996). Toe-Scour Estimation in StabilizedBendways, ASCE Journal of Hydraulic Engineering, Vol 122, No. 8.

Regarding the R/W limitation of 2, my recollection is that we believedthat few cases were less than 2 and that 2 was likely close to a

maximum. Regarding velocities, our EM 1110-2-1601, Hydraulic Design of

Flood Control Channels has our empirical equations for velocity innatural and trapezoidal channel bends. I have been told that manualcan be downloaded from our website.

Steve Maynord

EM 1110 2 1601 US A 1994
http://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htm


23/46

EM 1110-2-1601, US Army, 1994

http://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htm

EM 1110-2-1601

R t t i
http://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htmhttp://www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1601/toc.htm


24/46

Revetment in

bends

S d


25/46

http://www.ctre.iastate.edu/pubs/midcon2003/ettemascour.pdf

Robert Ettema, Tatsuaki Nakato, and Marian Muste

Scour around spur

dikes/groynes


26/46


27/46

Scour at groyns, Schiereck 2002, H-04

3/2

0 2.2

bB

Qhh se Eq. 4.9

Breusers/Raudkivi, 1991

ho= water depth

hse= scour depth

Q = discharge

(constant 2.2 is not dimensionless)

Expression of Ahmed for scour spur dikes as


28/46

Expression of Ahmed for scour spur dikes as

given by Hoffmans & Verheij (Scour Manual,

1997) reads:


29/46

Scour at bridges


30/46

S f S f c ( ) ( ) or

scour around a cilinder

Or, S = f(uuc)


31/46

scour around a cylinder as function

of waterdepth and diameter


32/46

Example of scour formula, Schiereck, 2001, H-04

Pier shape l/b K S

Cylinder

Rectangular

Elliptic

-

1

3

5

2

3

5

1.0

1.2

1.1

1.0

0.85

0.8

0.6

DhKKK

Dh uSs

0tanh2 not in example 4.1 ??

Ks= shape factorK= angle of attack

Ku= velocity factor

Ku= velocity factor :

Ku= 0 for u/uc< 0.5,Ku= 1 for u/uc> 1 andKu= (2u/uc- 1) for 0.5 < u/uc< 1

A constant of proportionality of 2 is recommended by Breusers et al,1977, for design purposes

Schiereck Example 4-1; cylindrical piers


33/46

Schiereck, Example 4 1; cylindrical piers

A cylindrical pier with a diameter of 5 m is located in ariver, 5 m deep, with a gravel bed, d50 = 5 mm. The flowvelocity is 1 m/s. What is the expected scour depth?

The dimensionless diameter, d*, in the Shields-Van Rijngraph, see figure 3.2b, is: 0.005*((1.65*9.81)/(1.33*10-6)2)1/3 = 105. This gives = 0.05 (Note: scour refers to

sediment transport, not to damage to a bottom protection,

so, the original Shields values should be used). With anassumed roughness of twice the median grain diameter we

find C = 18log(12*5/0.01) = 68 m/s. From this we find acritical velocity: uc = 68*(1.65*0.005*0.05) = 1.38 m/s.The velocity coefficient in equation 4.7 then becomes:

2*1/1.38-1=0.45. The scour depth becomes:5*0.45*tanh(5/5) = 1.7 m.

Or, with a proportionality factor of 2: hs= 2 x 1.7 = 3.4 m

Schields; Schiereck H-03; Fig 3-2


34/46

Schields; Schiereck H-03; Fig. 3-2

Figure 3-2 Critical shear stress according to Shields - van Rijn

Uc= C (dn50 )^0.5


35/46

Bridge scour protection

Stability of protection material can be calculated based on theassumption that the maximum shear stress and maximum flow velocity

near the cylinder are roughly equal to:

max= 4undisturbed

And/or umax = 2uundisturbed

Tere is a large number of formulas:


36/46

HEC-18 USA

Tere is a large number of formulas:


37/46

Example from USA:

y1 = average flow depth upstream

http://www.haestad.com/library/books/FMRAS/FloodplainOnlineBook/javascript/wwhelp/w

whimpl/common/html/wwhelp.htm?context=Floodplain_with_HEC_RAS&file=Floodplain%20with%20HEC-RAS-22-06.html


38/46


39/46


40/46

Reference

Title:Bridge Scour

Authors:Bruce W. Melvilleand Stephen E. ColemanSpecifications:Soft Cover, 572pp, ISBN 1-887201-18-1Price:US $85Cat No:BSR

"A comprehensive state-of-the-art treatment of scour andbridge foundations - both a handy reference text and amanual for the practicing bridge designer."
http://www.wrpllc.com/authors/melcole.htmlhttp://www.wrpllc.com/authors/melcole.htmlhttp://www.wrpllc.com/authors/melcole.htmlhttp://www.wrpllc.com/authors/melcole.html


41/46

R t t


42/46

Revetments

- Scour

- Toe protection

Rule of thumb:

Max Scour hole = height of local waveDepth limited :

Local wave height = 0.5 water depth

Thus, max scour depth = 0.5 water depth


43/46

Conclusions

Integrated approach:

Hydraulic aspects

Geotechnical aspects

Structural aspects


44/46

Literature

See also selected literature in lectures by Pilarczyk

http://www.unesco-ih / /di /b k80/d f lt ht ?htt //


45/46

ihe.org/we/dicea/brk80/default.htm?http://www.unesco-

ihe.org/we/dicea/brk80/brk8001.htm

Dicea overview:

CLO06 Bed protection near closure works

CLO0601 Function of a bed protection

CLO0602 Stability of a bed protection

CLO0603 Length of a bed protection

CLO0604 Calculation of a scouring hole

CLO0611 Stability under current attack

CLO0613 The Knauss and TAW formula (CRESS routine 612)

CLO0616 The Shields and Pilarczyk formula (CRESS routine 611)

download RWS-Cress (English version)

download IHE-Cress (Windows version)

Also:http://ikm.nl/rwscress/
http://www.unesco-ihe.org/we/dicea/clo06/clo0601.htmhttp://www.unesco-ihe.org/we/dicea/clo06/clo0602.htmhttp://www.unesco-ihe.org/we/dicea/clo06/clo0603.htmhttp://www.unesco-ihe.org/we/dicea/clo06/clo0604.htmhttp://www.unesco-ihe.org/we/dicea/clo06/clo0613.htmhttp://www.waterbouw.tudelft.nl/public/ct4310/cress/rwscressEN.ziphttp://www.ihe.nl/we/dicea/cress.htmhttp://www.ihe.nl/we/dicea/cress.htmhttp://www.ihe.nl/we/dicea/cress.htmhttp://www.ihe.nl/we/dicea/cress.htmhttp://www.waterbouw.tudelft.nl/public/ct4310/cress/rwscressEN.ziphttp://www.waterbouw.tudelft.nl/public/ct4310/cress/rwscressEN.ziphttp://www.waterbouw.tudelft.nl/public/ct4310/cress/rwscressEN.ziphttp://www.unesco-ihe.org/we/dicea/clo06/clo0613.htmhttp://www.unesco-ihe.org/we/dicea/clo06/clo0604.htmhttp://www.unesco-ihe.org/we/dicea/clo06/clo0603.htmhttp://www.unesco-ihe.org/we/dicea/clo06/clo0602.htmhttp://www.unesco-ihe.org/we/dicea/clo06/clo0601.htm


46/46

The end

Questiona and discussion

02_scour and protection

Documents