FLOOD11629 ‎(2)‎

• County: Statewide
• Basin: Statewide
• Title: Hydrologic Basin Response - Phase II B - Parameter Estimation Guidelines
• Date: 3/1/2007
• Floodplain - Doc Type: Floodplain Report/Masterplan

RTIMP % reduction ion urban T~
2 22
5 44
10 56
20 66
40 73
60 77
80 79
100 81
Therefore care must be exercised in estimating RTIMP using the best available
information such as high resolution aerial photographs.
6. Ideally, the selection of the watershed or subbasin boundaries can be made so
that the area represents a hydrologically uniform region that is essentially all one
physiographic type and for those situations, the appropriate T~ equation is
applied. However, there will be situations where the watershed or modeling
subbasin is a mi~ure of two or more physiographic types. In those cases, the T~
equation is selected based on the watershed type that contains the greatest
portion of L. The effects of a mixture of watershed physiographic types can be
partially accounted for by the selection of the time-area relation.
S$oraae Coefficient: The storage coefficient relates the effects of direct runoff storage in the
watershed to unit hydrograph shape. The equation for estimating the storage coefficient (R) is:
R= 0.37 T~l.~l Lso A-s~
where R is in hours and the variables are as defined for the T~ equations.
19 March 2007 1~