cee5734_hw3_2011_solutions

cee5734_hw3_2011_solutions - Virginia Tech Department of...

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Unformatted text preview: Virginia Tech Department of Civil and Environmental Engineering CEE 5734 – Urban Hydrology and Stormwater Management Homework #3: The SCS Tabular Method and Determination of Detention Storage Solutions Watershed Characteristics Table for Problems 1 – 3. Sub-Area Area (mi 2 ) Curve Number T c (hrs.) 1 1.37 73.2 1.53 2 0.91 79.1 0.69 3 1.18 69.7 1.27 For the channel conveying flow from sub-areas 1 and 2 and traversing sub-area 3, use n = 0.050, slope = 0.008 ft/ft, R = 1.5 ft, length = 3770 ft. Calculations: 1. The following two pages show worksheets 5a and 5b completed for the system described above. Travel time through sub-area 3 is calculated as shown below: s ft 49 . 3 008 . 5 . 1 050 . 49 . 1 49 . 1 2 / 1 3 / 2 2 / 1 3 / 2 S R n v hr 30 . hr s 3600 s ft 49 . 3 ft 3770 v L T t The overall peak discharge from hand calculations is 1484 ft 3 /s – use Q p = 1500 ft 3 /s. 2. The subsequent two pages show the VTPSUHM output for the same problem as in #1. VTPSUHM gives a peak discharge of Q p = 1404 ft 3 /s – call it Q p = 1400 ft 3 /s. The methods differ by a bit under 100 ft 3 /s, or about a 6% difference. This agreement is likely within the noise level of the tabular method overall. Differences are a result of different approaches for interpolation of I a /P ratios and different rounding rules for T c and T t . The page after the VTPSUHM output shows the comparison of the two hydrographs showing that the most substantial difference between these two hydrographs is in the neighborhood of the peak. 10...
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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_hw3_2011_solutions - Virginia Tech Department of...

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