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

Drainage Design Manual for Maricopa County
Hydrology: Application
1. Point Rainfall Depth: From Figure A.58 and Figure A.60 of APPENDIX A,
P 6
100
=
2.70 inches
P 24
100
= 3.62 inches
2. Depth - Area Reduction Factors: Inspection of Figure 9.1 yields the following:
• Subbasin areas range from 0.83 to 22.87 square miles
• Drainage areas at concentration points (CP) range from 0.44 to 22.9 square miles
• Selected index areas and corresponding depth-area reduction factors from Table
2.1 or Figure 2.1 for the 6-hour storm, and Table 2.2 or Figure 2.2 for the 24-hour
storm are:
6-hour
24-hour
Area
sq. miles
Depth-Area
Reduction Factors
Area
sq. miles
Depth-Area
Reduction Factors
0.01 1.000 0.01 1.000
0.50 0.994 0.50 0.998
2.80 0.975 2.00 0.990
16.00 0.922 10.00 0.950
25.00 0.900 25.00 0.909
Rainfall Distribution
3. The 6-hour pattern numbers corresponding to the selected index areas are 1, 2, 3 and
3.3.
Dimensionless rainfall distributions for pattern numbers 1, 2 and 3 are taken directly
from Table 2.4. The distribution for pattern number 3.3 is determined by linear interpolation
between pattern numbers 3 and 4 as listed in Table 2.4. The dimensionless
distribution for pattern number 3.3 is:
9-6 August 15, 2013