cee5734_hw2_2011_solutions_2011

cee5734_hw2_2011_solutions_2011 - Virginia Tech Department...

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1 Virginia Tech Department of Civil and Environmental Engineering CEE 5734 – Urban Hydrology and Stormwater Management Homework #2: The SCS/NRCS Graphical Peak Discharge Method Solutions 1. Use the Rational Method and accompanying analysis/design methods to determine inlet size and pipe diameter for Area 2 and Pipe 2-3 in the system provided. For a 10-year frequency, 15 minute Tc duration, the Blacksburg rainfall intensity is 3.82 in/hr. a. Peak discharge (in ft 3 /s) for area 2 (only) /s ft 9 . 8 ... 877 . 8 ) 3 . 8 )( 82 . 3 )( 28 . 0 ( 3 ciA Q p b. Inlet size (in ft 2 ) for area 2 (only). (Assume an orifice, with a h 2 = 0.62 ft, C o =0.6 for both inlets and f s = 0.5 for both inlets.) gh A C Q o 2 Rearranging for A: ... 341 . 2 ) 62 . 0 )( 2 . 32 ( 2 60 . 0 9 . 8 2 1 1 2 gh C Q A o But there’s a factor of safety of f s 0.5 so: 2 2 ft 7 . 4 .. 341 . 2 s f A c. Pipe diameter (in inches) for Pipe 2-3 (only). Here there is an extra step from last week’s homework. We need to determine what discharge is greatest. There are three possibilities: Area 1’s discharge alone (9.6 ft 3 /s acting at a total Tc not yet calculated) Area 2’s discharge alone (8.9 ft 3 /s at 15 minute Tc) Composite Area 1 and Area 2 at the maximum of these two area’s Tc’s (not yet calculated). For Area 1. The total Tc is the Tc for Area 1 itself, plus the travel time down the pipe. Tc for Area 1 was given as 10 minutes. The travel time down the pipe is the pipe length divided by the velocity. To calculate the velocity in the pipe, we need to use the circular properties chart for a 30 inch pipe (calculated in Week 1).
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This note was uploaded on 12/24/2011 for the course CEE 5734 taught by Professor Moglen during the Spring '11 term at Virginia Tech.

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cee5734_hw2_2011_solutions_2011 - Virginia Tech Department...

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