01 to a tree lined floodplain n 015 due to the

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Unformatted text preview: s and roughness, the scatter bands in Table 10.1 should be taken seriously. Since Manning’s sixth-root size variation is not exact, real channels can have a variable n depending upon the water depth. The Mississippi River near Memphis, Tennessee, has n 0.032 at 40-ft flood depth, 0.030 at normal 20-ft depth, and 0.040 at 5-ft low-stage depth. Seasonal vegetative growth and factors such as bottom erosion can also affect the value of n. EXAMPLE 10.1 A finished-concrete 8-ft-wide rectangular channel has a bed slope of 0.5° and a water depth of 4 ft. Predict the uniform flow rate in ft3/s. Solution Part (a) From Table 10.1, for finished concrete, n 0.012. The slope S0 y 4 ft and width b 8 ft, the geometric properties are A by (8 ft)(4 ft) Rh A P 32 ft2 P b 2y tan 0.5° 8 2(4) 0.00873. For depth 16 ft 2 32 ft 16 ft 2.0 ft Dh 4Rh 8.0 ft From Manning’s formula (10.19) in BG units, the estimated flow rate is Q 1.486 2/3 1/2 ARh S0 n 1.486 (32 ft2)(2.0 ft)2/3(0.00873)1/2 0.012 590 ft3/s Ans. *An inter...
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This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.

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