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Geology 653—Hydrology

Text 1.24  graph the infiltration curve

Given an initial rate of infiltration equal to 1.25 in./hr and a  final capacity of 0.25 in./hr, use Horton’s equation [Eg. (1-20)] to find the infiltration capacity at the following times: t = 10 min, 15 min, 30 min, 1 hr, 2 hr, 4 hr, 6 hr.  You may assume a time constant k = 0.25 hr-1.
Text 1.26 show a plot of the infiltration curve and hyetograph in addition to the plot of overland flow.

A 5-hr storm over a 15-ac basin produces a 5-in. rainfall:  1.2 in./hr for the first hour, 2.1 in./hr for the second hour, 0.9 in./hr for the third hour, and 0.4in./hr for the last two hours.  Determine the infiltration that would result from the Horton model with k = 1.1 hr-1 , fc = 0.2 in./hr, and fo = 0.9 in./hr.  Plot the overland flow for this condition in in./hr vs. t.

Text 1.30

A sandy loam has an initial moisture content of 0.18, hydraulic conductivity of 7.8 mm/hr, and average capillary suction of 100 mm.  Rain falls at 2.9 cm/hr, and the final moisture content is measured to be 0.45.  Plot the infiltration rate vs. the infiltration volume, using the Green and Ampt method of infiltration.

Using the SCS curve number method, determine the initial abstraction in inches for a soil type A in both an open space grassy area and a paved parking lot.  Based on the chart (you may check with the equations) how much rain in inches would be required before you would have direct runoff in both cases.