An unfinished concrete semicircular channel with diameter of 3 ft is used to transport water over a distance of 1 mile. if flow is 90 ft3/s when the channel is full, calculate the minimum elevation difference in ft.

448.8 ft

Explanation:

Area of semi-circle=

Hydraulic radius is given by

where is wetted perimeter, is cross-sectional flow area and is hydraulic radius

From Manning’s equation, flow rate is given as

Here, is bottom slope,

Manning’s coefficient is taken as n=0.014 for open unfinished concrete

Substituting 90 for v, 1.486 for a, 3.5325 for , 0.74 for and 0.014 for n

Change in elevation is given by

where L is distance, here given as 1 mile

1 mile=5280 ft

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