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

Drainage Design Manual for Maricopa County
Hydrology: Indirect Methods
8.4 INDIRECT METHOD NO. 3 - REGIONAL REGRESSION
EQUATIONS
An analysis was performed of streamflow data for a study area comprised of Arizona, Nevada,
Utah, and parts of New Mexico, Colorado, Wyoming, Texas, Idaho, Oregon, and California
(USGS Open File Report 93-419, 1994). That analysis resulted in sixteen sets of regional
regression equations for the study area. Two of those regions (R12 and R13) are in Maricopa
County as shown in Figure 8.6. These regional regression equations can be used to estimate
flood magnitude-frequencies for watersheds in Maricopa County.
Regression equations are provided for both regions to estimate flood peak discharges for frequencies
of 2-, 5-, 10-, 25-, 50-, and 100-years. Use of the regression equations is recommended
only if the values of the independent variables (drainage area and mean basin elevation)
for the watershed of interest are within the range of the database used to derive the specific
regression equation.
The regression equations for both regions (R12 and R13) are functions of drainage area. In general,
the equations are applicable to unregulated watersheds with drainage areas less than 200
square miles. The regression equation for Region 12 is also a function of mean basin elevation.
Figure 8.7 is a scatter diagram of mean basin elevation versus drainage area for the database
used to derive the regression equations as provided in USGS Open File Report 93-419.
The regression equations for Regions 12 and 13 are provided in Table 8.2 and Table 8.3, respectively.
Also provided for each set of regression equations are graphs, Figure 8.8 and Figure 8.9, of the
100-year LP3 discharge estimates versus drainage area for Flood Regions 12 and 13, respectively.
A line depicting the relation between the 100-year peak discharge (computed from the
regional regression equation) and drainage area is shown on each of those graphs. These
graphs were recreated from the data provided in USGS Open File Report 93-419.
8-12 August 15, 2013