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).
 | If you wish to use a different peak factor, you must
select a different unit hydrograph on the UH tab of the Settings|Calculation.
|
 | To 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.
|