CEWB223 - Channel Geometry

5/21/2018 CEWB223 - Channel Geometry

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Dr. Mohd Hafiz bin Zawawi

Hydraulic Engineering

CEWB

CHAPTER 2

(OPEN CHANNEL PROPERTIES)


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Natural channel

All watercourses that occurs naturally, for example streams

and rivers

The Hydraulic properties are generally irregular

Not regular nor prismatic and their materials of construction

can vary widely.

The surface roughness will often change with time distance

and even elevation.

Types of open channel


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Man-made channel

Constructed in a regular cross-section shape throuhout and thusare PRISMATIC CHANNELS.

Made from concrete, steel or earth with well defined surfaceroughness.

All watercourses that are constructed by human effort, forexample :



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Canal : a long and mild-sloped channel built in the ground thatmay be unlined or lined with stone masonry, concrete ,etc.

Flume : a channel of concrete, masonry, etc that is usuallysupported on or above the surface of the ground to conveywater across a depression.

Chute : a channel with steep slopes.

Culvert : a covered channel of comparatively short length

installed to drain water through highway and railroadembankments.



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Canal


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Trunk Drain - Wet Period

Rigid Boundary Canal


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FLUME


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Existing Culvert


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Existing Pipe Culvert


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Existing Box Culvert


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Prismatic channel : a channel with

unvarying cross section and constant

bottom slope. Non-prismatic channel : a channel

with varying cross section and

constant bottom slope.

Channel Geometry


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CHANNEL GEOMETRY


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Rectangular

Properties and geometric elements of

typical channel cross section

Area

, A

Wetted

perimeter,

P

Hydraulic

Radius, R

Top

Width, B

Hydraulic

depth, D

by b + 2y

by /

(b+2y) b y


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Trapezoidal

Properties and geometric elements of typical

channel cross section

Area, A

Wetted

perimeter, P

Hydraulic

Radius, R

Top Width,

B

Hydraulic

depth, D

(b + ty)y

b + 2yw

w= (1+ t2)0.5 A/P b + 2ty A/B


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Triangular



Area

, A

Wetted

perimeter,

P

Hydraulic

Radius, R

Top

Width, B

Hydraulic

depth, D

ty2 2yw ty / (2w) 2ty A/B


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Circular



Area, A

Wetted

perimeter,

P

Hydraulic

Radius, R

Top Width,

B

Hydraulic

depth, D

( - sin ) d2/8 r

(1 - sin/)

d/4 2r sin(/2) A/B


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Semi circular



Area, A

Wetted

perimeter,P HydraulicRadius, R Top Width,B Hydraulicdepth, D

r2/2 r r/2 2r r/4


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RECTANGULAR CHANNEL

TArea (A) = by

Wetted perimeter (P) = b+2y

Hydraulic Radius (R) = A/P=y2b

by

Top width (T) = b

Hydraulic Depth (D) = y

b

y


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TRAPEZOIDAL CHANNEL

Area = (b+zy)y

P =212 zyb

212

)(

zyb

yzyb

R =

T = zyb 2

D =zyb

yzyb

2

)(

y

b

z

1

T


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A concrete rectangular channel has a bottom

width of 4 meters. If the channel is on a 1%slope and is flowing 1 meter deep throughout its

length, what is the cross sectional area, wetted

perimeter and hydraulic radius?

Example 1


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Solution:

If the shape of the channel is rectangular, thedischarge computed as follows:

A = by = (4) (1) = 4m2

P = b+2y = 4 + 2 (1) = 6m

R = 4m2/ 6m = 0.67m

T

4

1


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A concrete trapezoidal channel has a bottom width of 4

meters and 45side slopes. If the channel is on a 1%

slope and is flowing 1 meter deep throughout its

length, what is the cross sectional area, wetted

perimeter and hydraulic radius?

Example 2


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Solution:If the shape of the channel is trapezoidal, the discharge

computed as follows:

A = (b+zy)y = (4+(1)(1))1 = 5.00m2

P = (b+ 2y (1+ z2)0.5)= 4 + 2 (1) (2)0.5= 6.83m

R = A/P = 5.00m2/6.83m = 0.73m

Example 2

T

4

1 11


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Water flows at a depth of 1.83 m in a trapezoidal,

concrete-lined section with a bottom width of 3 m and

side slopes of 2:1 (H:V). The slope of the channel is

0.0005 and the temperature is 20oC. Assuming uniformflow conditions, estimate the cross sectional area (A),

wetted perimeter (P) and hydraulic radius (R)?

Example 3


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Solution:Flow area, A = (b+zy)y = (3 + 2 (1.83)) x 1.83

= 12.2 m2

Wetted perimeter, P = 14.89m

Hydraulic Radius, R = A/P = 12.2/ 14.89 = 0.819 m


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Example 4


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TEXTBOOKS REFERENCES

Lariyah, M.S. & Norazli, O., Hydraulic Notes,

UNITEN, 2006

Roberson, J. A., Cassidy, J. J. & Chaudry, H.,Hydraulic Engineering, 1st S.I. Ed., John

Wiley, 1998

Chin, D., Water Resources Engineering,Prentice Hall, 2006


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Thank You

CEWB223 - Channel Geometry

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