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

Drainage Design Manual for Maricopa County
Hydrology: Rainfall Losses
eter values for drainage areas can result in the generation of no rainfall excess which may or
may not be correct. Incorrect results could cause serious consequences for flood control planning
and design. Therefore, it is recommended that, for watersheds consisting of relatively small
subareas of sand, the Green and Ampt parameter values for loamy sand be used for the sand
portion of the watershed. If the area contains a large portion of sand, then either the Green and
Ampt method should be used with the parameter values for loamy sand or the IL+ULR method
should be used with the appropriately determined values for the parameters.
Table 4.1
GREEN AND AMPT LOSS RATE PARAMETER VALUES FOR BARE GROUND
Soil Texture XKSAT PSIF DTHETA 1
Classification inches/hour inches Dry Normal Saturated
(1) (2) (3) (4) (5) (6)
loamy sand & sand 1.20 2.4 0.35 0.30 0
sandy loam 0.40 4.3 0.35 0.25 0
loam 0.25 3.5 0.35 0.25 0
silty loam 0.15 6.6 0.40 0.25 0
silt 0.10 7.5 0.35 0.15 0
sandy clay loam 0.06 8.6 0.25 0.15 0
clay loam 0.04 8.2 0.25 0.15 0
silty clay loam 0.04 10.8 0.30 0.15 0
sandy clay 0.02 9.4 0.20 0.10 0
silty clay 0.02 11.5 0.20 0.10 0
clay 0.01 12.4 0.15 0.05 0
Notes:
1. Selection of DTHETA
Dry = Nonirrigated lands, such as desert and rangeland;
Normal = Irrigated lawn, turf, and permanent pasture;
Saturated = Irrigated agricultural land.
4-10 August 15, 2013