Drainage Design Manual, Hydrology - Flood Control District of ...

Drainage Design Manual for Maricopa County
Hydrology: Application
Consider the 2-year frequency storm of 5-minute duration:
Apply Equation (9.1) for all storm durations and frequencies to create the data in Table
9.2.
Duration
9.1.3.2 Rainfall for the Unit Hydrograph Method
Problem:
Solution:
2
= ------------
0.30
= 3.60 inches ⁄ hour
5 ⁄ 60
j 0.083
Table 9.2
EXAMPLE COMPUTED INTENSITY-DURATION-FREQUENCY DATA
(using Table 9.1)
Point Rainfall Intensity Data in inches/hr
For the 22.87 square mile watershed shown on Figure 9.1, determine the following for a
100-year multiple storm analysis:
1. Point rainfall depth,
2. Depth-area reduction factors, and
3. Rainfall distributions.
Storm Frequency, years
2 5 10 25 50 100
5-min 3.60 4.80 5.16 6.36 7.32 8.40
10-min 2.46 3.24 4.08 4.92 5.58 6.36
15-min 2.08 2.80 3.32 4.08 4.68 5.24
30-min 1.40 1.86 2.24 2.76 3.16 3.56
1-hour 0.86 1.17 1.40 1.70 1.95 2.20
2-hours 0.49 0.66 0.79 0.96 1.10 1.23
3-hour 0.34 0.45 0.54 0.65 0.74 0.83
6-hour 0.20 0.25 0.30 0.36 0.40 0.45
12-hour 0.11 0.14 0.16 0.20 0.22 0.24
24-hour 0.06 0.08 0.10 0.12 0.13 0.15
Given the watershed size, both the local storm (6-hour) and the general storm (24-hour) are to be
considered (refer to Section 2.1.2).
August 15, 2013 9-5