Question

Rain fell over a 1490-acre watershed at a constant rate of 2.75 inches/hour from 9 to 11 AM. Stream flow data recorded each hour are reported below. Note that the stream flow declines in dry periods to a relatively constant lower limit of 100 cfs (ft3/s). (a) Separate the base flow from the hydrograph. (b) When did direct (i.e., storm) runoff begin and end? (c) Find Pe,, the depth of excess precipitation, in inches. (d) Derive the 2-hour unit hydrograph.

DATA

clock time 9 10 11 12 1 2 3 4 5 6

total Q (cfs) 100 300 500 700 800 600 400 300 200 100

Answer #1

The net precipitation (runoff) in a three-hour period was 0.6
inches. The direct runoff hydrograph that resulted from this
precipitation was in the form of a triangle with a time base of 21
hours and with a peak flow of 200 cfs that occurred 9 hours from
the beginning of the runoff.
(a) Sketch the direct runoff hydrograph. Be sure to label
axes.
(b) Determine the runoff volume (ft3)
(c) Determine the drainage area (acres)
(d) Sketch the unit hydrograph...

Apply the Modified Rational Method to a 7 acre watershed with a
time of concentration of 0.80 hours and a runoff coefficient of
0.7.
a.Determine and plot the direct runoff hydrograph for a 1-hour
storm that drops 2 inches of rain. What is the peak flow, time to
peak, and base time?
b.Determine and plot the direct runoff hydrograph for a
10-minute storm that drops 0.8 inches of rain. What is the peak
flow, time to peak, and base time?

After a 2 hour storm, a station downstream from a 45 mi2
drainage watershed records a peak discharge of 9400 cfs and a total
runoff of 3300 acre-ft.
(a) what is the unit hydrograph peak discharge?
(b) what would be the peak runoff and design flood volume if a 2
hour storm dropped 2.5 inch net precipitation?

Part I. Indicate whether true or false (T or F).
____ Storm water detention ponds typically are designed to
regulate the outflow peak rate at or below a single target value,
such as the pre-development (pre-land use change) peak runoff rate
for a specified return period event. Detention storage alters the
peak but not the volume of the outflow hydrograph.
_____ Typical rating curves for weirs are concave upward.
Typical rating curves for orifices are concave downward.
____ A sediment...

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