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Scour Cal

This document summarizes the design of scour protection at the toe of a trapezoidal slope section. It provides the equations and calculations to determine: 1. The maximum scour depth of 3.5 meters based on Lacey's scour depth equation and channel geometry. 2. The apron length of 5 meters to protect against this scour depth. 3. The minimum stone size of 500 mm to resist movement based on the average flow velocity of 3 meters per second.

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172 views2 pages

Scour Cal

This document summarizes the design of scour protection at the toe of a trapezoidal slope section. It provides the equations and calculations to determine: 1. The maximum scour depth of 3.5 meters based on Lacey's scour depth equation and channel geometry. 2. The apron length of 5 meters to protect against this scour depth. 3. The minimum stone size of 500 mm to resist movement based on the average flow velocity of 3 meters per second.

Uploaded by

Anonymous O404LiV4C
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as XLS, PDF, TXT or read online on Scribd
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SCOUR PROTECTION AT TOE OF TRAPEZOIDAL SECTION SLOPE

Scour depth relationship- Lacey's theory


Shape of regime channel

R
D

R = 1.35 (q2/f)1/3 1
where R= Hydraulic mean readius (A/P)
q= Discharge perunit width (m2/s/m)
f= Lacey's silt factor for typical of bedding material
(taken as 1.25 for medium sand)
Average width of channel flow B = 25 m
Discharge Q = 208.45 m3/s
q = 8.34 m3/s/m

From Lacey's scour depth equation (equation 1 )


R = 5.15 m

Maximum depth for channel D = multipying factor (F) x R F = 1.25 straight channel
D = 6.44 m

H
D

Average depth of flow, H = 3 m


Scour Depth, d = D - H = 3.44 m say 3.50 m

Freeboard
Slope Stone
Apron Stone R
1.5d
T'

1 d
1.25T
1.5

Apron Length 1.5d = 5.25 m SAY 5 m

Maintaining the same volume of arpon stone


1.5d x T' = 1.25 T x sqrt( 5) x d 2
or T' = 1.25/1.5 x T sqrt (5)

From the hydraulic analysis, the average velocity is 3 m/s

According to the atached figure 165- curve to determine maximum stone size riprap
From the figure for velocity = 3 m/s = 9.84 ft/s

The minimum size to resist movement is 14 inches or 350 mm


USE 500 mm
From Equation 2 T' = 652 mm say 800 mm

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