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These are the Problems of Advanced Hydrology which includes Excess Ordinate, Data, Area Method, Histogram, Calculation, Contribution etc.Key important points are: Area, Method, Appropriate Shape, Duration Rainfall, Duration Of Rainfall, Small Watershed, Distributed
Typology: Exercises
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Use Snyder’s method to develop a UH for the area of 100mi2 described below. Sketch the appropriate shape. What duration rainfall does this correspond to? Ct = 1.8, L= 18mi, Cp = 0.6, L (^) c= 10mi
Calculate t (^) p t (^) p = Ct (LL (^) C) 0. = 1.8(18·10) 0.3^ hr, = 8.6 hr
Calculate Qp Qp = 640(c (^) p )(A)/t (^) p = 640(0.6)(100)/8. = 4465 cfs
Since this is a small watershed, Tb ≈4tp = 4(8.6) = 34.4 hr
Duration of rainfall D= t (^) p /5.5 hr = 8.6/5.5 hr = 1.6 hr Docsity.com
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Q (cfs
)
Time (hr)
Qp
W (^75)
W (^50) Area drawn to represent 1 in. of runoff over the watershed
W 75 = 440(Q (^) P/A) -1. W 50 = 770(Q (^) P/A) -1. (widths are distributed 1/3 before Q (^) p and 2/3 after)
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Find TR using eq.
Given rainfall duration is 2 hr, TR = 4.36 hr, the rise of the hydrograph Then find Qp using the eq, given A= 10 mi 2
. Hence Qp = 1.110 cfs
R
p
To complete the graph, it is also necessary to know the time of fall B. The volume is known to be 1 in. of direct runoff over the watershed. So, Vol. = (10mi 2 ) (5280ft/mi) 2 (ac/43560ft 2 ) (1 in.) = 6400 ac-in Hence from eq.
B = 7.17 hr
p R p
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Q (cfs
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Time (hr)
Qp = 1110 (cfs)
T (^) R=4.36 (hr) B=7.17 (hr)
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Time (hr) Discharge (cumec) 0 0 2 25 4 100 6 160 8 190 10 170 12 110
Time (hr) Discharge (cumec) 14 70 16 30 18 20 20 6 22 1. 24 0
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Time (hr) 0 9 18 27 36 45 54 63 72 81 90
Flow (cumec)
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