Metric Problems

The hydraulic cycle is same regardless of the units being used. The only difference is in the units used to measure rainfall. The rainfall-intensity-duration graph included in this section with SI units looks different because it is not a logarithmic graph, Figure 16.10.

Problem: Determine the rainfall intensity for a 5 year storm and duration of 20 min using SI units

15.0

15.0

Duration (minutes & hours)

FIGURE 16.9. Rainfall intensity for sample problem.

Duration (minutes & hours)

FIGURE 16.9. Rainfall intensity for sample problem.

FIGURE 16.10. Rainfall Intensity—duration-reoccurrence interval graph with SI units.

Solution: Enter Figure 16.11 along the horizontal axis at the 20 min mark and move vertically to the 5 year storm curve and then move horizontally left to the rainfall intensity scale. Read rainfall intensity = 72 mm/hr.

Problem: What is the expected recurrence interval for a storm with a duration of 28 min and an intensity of 70 mm/min?

Solution: Move upward from 28 min duration and to the right from 70 mm/hr, Figure 16.12. At the point were they converge read 10-year interval.

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