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

Drainage Design Manual for Maricopa County
Hydrology: Application
Solution:
1. Select Runoff Coefficients (C) for each land use from the range of values in Table 3.2. This
watershed is within unincorporated Maricopa County. Therefore, the following values are from
the Drainage Policies and Standards for Maricopa County, Arizona (2007).
Hillslopes, Sonoran Desert (NHS) C = 0.69
Undeveloped Desert Rangeland (NDR) C = 0.50
Low Density Residential (LDR, 130) C = 0.60
Medium Density Residential (MDR, 140) C = 0.71
Multiple Family Residential (MFR, 170) C = 0.94
Pavement (P, 2002) C = 0.95
Compute the arithmetically area-weighted C value for subbasins S1 through S4.
Subbasin S1:
Subbasin S2:
( 0.69) ( 54.72) + ( 0.50) ( 11.27)
C w = ------------------------------------------------------------------------- =
( 65.99)
0.66
C w = 0.50
Subbasin S3:
( 0.50) ( 11.85) + ( 0.94) ( 8.39) + ( 0.95) ( 0.94)
C w = ------------------------------------------------------------------------------------------------------------ =
( 21.18)
0.69
Subbasin S4:
( 0.50) ( 2.07) + ( 0.60) ( 16.50) + ( 0.71) ( 6.64) + ( 0.95) ( 2.59)
C w = ------------------------------------------------------------------------------------------------------------------------------------------------- = 0.65
27.80
The runoff coefficients for each subbasin are:
S1: C = 0.66
S2: C = 0.50
S3: C = 0.69
S4: C = 0.65
9-16 August 15, 2013