HydroCAD UNIT HYDROGRAPH Defintions
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            Copyright (c) 2006 HydroCAD Software Solutions LLC
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NOTE: Most HydroCAD projects may be completed by selecting one of
      the pre-defined unit hydrographs that are automatically
      installed with HydroCAD.  The information in this file is
      required ONLY in the rare situation that you need to define
      a custom unit hydrograph, or wish to know more about how the
      unit hydrograph data is defined.

      For additional information, plus other unit hydrograph files
      you can download, please see www.hydrocad.net/uhtables.htm

 
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HydroCAD provides a number of predefined Unit Hydrograph tables.  Starting
with HydroCAD-6, each table is stored in a separate file with a .huh
extension.  This allows any custom UH tables to be fully independent of
the standard tables supplied with HydroCAD.  If you previously defined
a custom UH, you must now create a separate file for each custom UH.

Each file contains a single Unit Hydrograph table.  The table is used with
the SCS Unit Hydrograph runoff procedure to define how a single burst of
runoff is distributed over time.

The predefined tables will accommodate the vast majority of all hydrology
projects.  Only in rare cases will it be necessary to add custom UH tables.
If you feel you need a curve that is not included, please contact HydroCAD
support to see if it has been added in a later release.

If the rare event that you do need to create a custom UH table, the format
of the UH files is described below.  Custom UH tables may be stored in the
HydroCAD\Rainfall folder, or in the same folder as the project(s) with
which they will be used.

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Each UH table consists of evenly-spaced points that define an intensity curve.
The first and last values must be zero.  The peak value is usually 1.00, but
this is not required, since HydroCAD will scale the UH by setting its integral
equal to the volume of each rainfall burst.  Note that the "peak factor" is
built into the table, and cannot be set independently.  If you want to use a
different peak factor, you must use a different unit hydrograph.

To dimension the time axis, HydroCAD will always locate the U.H. peak at
Tp=2/3 Tc.  The overall duration of the UH is determined by the duration of
the supplied data in relation to the time-to-peak.

For examples of the exact UH file format, see one of the standard tables in
SCS.huh or Delmarva.huh

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       **  The actual unit hydrograph tables used by         **
       **  HydroCAD are contained  in the HydroCAD\Rainfall  **
       **  folder. Custom rainfall files may also be stored  **
       **  in the same folder at the applicable project(s).  **
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To view any UH table, double-click the desired file. If asked what
program you want to use to open the file, select "notepad".

HydroCAD 8.0 (and later) also includes a special report window which
makes it easy to view, compare, and create UH definitions.  To open
the report select View | Unit Hydro from the main menu, or click the
"View UH" button on the calculation settings screen.