3:10 AM o etisalat o 68% HW-13.pdf Done ID: Channel Engineering Exercise Al Ain

Question

3:10 AM o etisalat o 68% HW-13.pdf Done ID: Channel Engineering Exercise Al Ain is partly built on alluvial fans that drain nearby mountains in Oman. The alluvial fans are visible on satellite photos. Some of the alluvial fan channels have been engineered to allow flood water from Oman to pass through Al Ain without fooding the city. You wi calculate the velocity and amount of flood water ie. discharge) that channels like these can hold without overflowing. You will then calculate what rock sizes could be transported by such food waters The following equation gives the relationship between flow velocity, slope, and channel velocity is a number representing "roughness" of the channel R hydraulic radius. S slope. Hydraulic radius (R) is the cross sectional area of the channel divided bythe "wetted" perimeter (e.g. 2A B in the channel cross section below). Cross section ofaflood control channel. The following represents the dimensions of one of the Al Ain channels: B-channel width 200 feet; A-channel depth 10 feet; S-slope -0.005 N-bed roughness coefficient 0.02. A slope of 0.00s is equivalent to 0.5 90 0.005. Use the value of 0.005 for the

Explanation / Answer

Calulation of Amount of discharge Al Ain Alluvial Fans stream in Oman

Disachage of stream= Area x Velocity

Velocity = V = (1.49/n) R2/3S1/2

n = number representing roughness of stream = 0.02

R =Hydraulic radious (2A+B) = A is depth and B is width of stream = Area of stream

                   2A = 2x 10=20ft

                   B = 200ft

          2A +B = 20 + 200 =220 sq. ft

          Area of the stream cross cut = 220 sq.ft

S= slope of stream = 0.005

Velocity                = (1.49/0.02) 2202/30.0051/2

                             = 74.5 x 146.6 x 0.0025

                             = 27.30 ft /s   = 8.3 m/s

Discharge = Q= A x V =Area x velocity

                   = 220 x 27.3 =6006

So the discharge of the stream is 6006 ft/s

                                                = 1830 m/s

6. Answers

Yes it is good idea to line channels with cobbles

Because cobble size varies from 64 to 256 mm. The stream velocity is such that it is depositing cobble size materials and transporting finer size less than 64mm

So lining of channel with cobbles will sustain stream velocity

and flooding . SO it is good to line channel banks with cobles

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