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HydroCAD® Stormwater Modeling - Since 1986

Unit Hydrographs

Unit Hydrographs

The SCS runoff procedure employs a Unit Hydrograph, which predicts the runoff hydrograph that will be produced by a short burst of rainfall.  (See the training slides for complete details.)  A prominent feature of the UH is the Peak Factor.  Most projects are performed with the default SCS unit hydrograph (PF=484) or the Delmarva unit hydrograph (PF=284).

bulletIf you wish to use a different peak factor, you must select a different unit hydrograph on the UH tab of the Settings|Calculation.
 
bulletTo examine the UH tables installed on your computer, click View|Unit Hydrograph:

The following unit hydrographs are included with HydroCAD-10.  Any files added after the initial release will be available for download from this page.

Name Notes
   
Delmarva Delmarva UH (PF=284)
Gamma-100
Gamma-150
Gamma-200
Gamma-250
Gamma-300
Gamma-350
Gamma-400
Gamma-450
Gamma-484
Gamma-500
Gamma-550
Gamma-600		 Gamma distributions with peak factors from 100 to 600.  Commonly used for applications where a site-specific UH table is not available.  For details see NEH Part 630, Hydrology, Chapter 16, 2007, Table 16B

Note: Gamma-100 and Gamma-150 were added in HyroCAD-10 build 22.
Georgia-300
Georgia-323
Georgia-484		 Georgia Stormwater Management Manual
Note: The Georgia tables are commonly used in Florida.
Michigan-369 Michigan UH with 28.5% of volume under the rising limb.
SCS Standard SCS UH (PF=484) Used for most projects.
SWFWMD-256 Southwest Florida Water Management District.
   

For rare applications that may require other peak factors, you can create a custom unit hydrograph file.  For details select Start|Programs|HydroCAD|Unit Hydrograph Info or see the UH.TXT file in the HydroCAD\Rainfall folder.
 


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