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HydroCAD Stormwater Modeling - Since 1986

HCE Format

Using HCE hydrograph files

An HCE file uses a special format to represent external hydrograph data.  It is frequently used with a link to interconnect two or more HydroCAD project files as described here.

HCE files can also be created manually, or generated by other software, according to the format described below.  Although the HCE file format is very flexible and powerful, when creating files by hand it's generally easier to use CSV format.

Creating an HCE file by hand

Custom HCE files may be created according to the specifications described below.

Sample Multi-Event file

Below is a simple HCE file that defines a hydrograph for two different rainfall events.  Each [hydrograph] section defines a separate hydrograph.  Note that both hydrographs have the same Name, but each one provides data for a separate Event.

Comment=Multi-Event Import example

Name=Off-Site Inflow
Flow= 0 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 0

Name=Off-Site Inflow
Flow= 0 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 5 0

The following data is defined within each hydrograph:

to (tee-zero) is the starting time for each hydrograph, in seconds.  This may be zero, or some larger value.  This parameter is comparable to the beginning of the calculation time span for each project, although the two values do not have to be the same.  (e.g. HydroCAD can automatically handle dissimilar hydrographs.)

dt (dee-tee) is the time increment between successive flow values, in seconds.  This is comparable to the time increment used within each project, but does not have to be the same.

Flow values appear on one or more lines, separated by spaces.  The first value defines the flow at time to.  The second value defines the flow at time to+dt, etc.  Flow values may be in CFS or m/sec, depending on the FileUnits parameter at the beginning of the file.  When defining the flow, note that a complete multi-point hydrograph is required.  A single flow value will define the flow at only one point in time, and the flow will be zero at all other times.

Area is the watershed area represented by this hydrograph.  This value is optional.  If present, it allows HydroCAD to report volumes as an equivalent depth, as well as the standard volumetric representation.  The value may be in square-feet or square meters, depending on the FileUnits parameter at the beginning of the file.

Defining a constant flow

Although a link will usually be used to import a time-varying flow (a hydrograph), there may be cases were the flow should be constant at all times.

bulletFor HydroCAD 7.13 and later, a constant flow may be defined by using a single flow value and omitting the dt parameter.  If desired, you can cause the flow to start at a specified by using the appropriate to value.  If you use to=0 (or omit the line entirely) the flow will start at time zero.
bulletFor earlier versions of HydroCAD, a constant flow can only be specified by defining a complete multi-point hydrograph, using the same value for each flow parameter.  For example, to define a constant flow over ten hours you could use:

Flow= 2 2 2 2 2 2 2 2 2 2 2

The hydrograph starts at time zero and uses a time increment of 1 hour (3600 seconds).  Note that the Flow line contains eleven values for hour 0,1,2...9,10

Creating your own file

You may create your own HCE file by following the sample format shown above.  You may use any text editor that is able to create a plain-text file.  Make sure you save the file with an .HCE extension, otherwise HydroCAD will not recognize the file.

To be sure you use the correct formatting, you may want to use this sample HCE file as a template.  You will also find additional details in the LinkTest1 file that is installed in your HydroCAD Project folder.

Using your HCE file

To use your data in a HydroCAD project, create a link node and use the "File" option to select your HCE file.  The outflow of the link will consist of your specified hydrograph, and may be routed just like any other node.

Important: Whenever you use a multi-event link, the associated project must contain rainfall events with the exact same event names used in the data file.  The events must be defined on the Rainfall tab of the calculation settings screen.

Demonstration multi-event link

For a demonstration of the hydrograph import capability, and the features of each file format, see the Link Demo project that is preinstalled with HydroCAD-10 and later.


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