HydroCAD Stormwater Modeling - Since 1986


Importing TR-20 data into HydroCAD

HydroCAD 8.5 provides a new capability to import a TR-20 data file directly into HydroCAD.  By using Project|Import|TR-20 most elements of a TR-20 file can be automatically converted to their equivalent operations in HydroCAD, eliminating most of the manual data entry that was previously required.

Although this process will import most of the data from a TR-20 data file, calculation results may vary because of the different techniques used in the two programs.  For details see the TR-20 comparison table.

For those using earlier versions of HydroCAD, this page can be used as a guide for manual data conversion.

How it works

The converted data is saved as a new HydroCAD project, without altering the original TR-20 file. The import procedure automatically applies settings from the "TR-20 Default" project, located in the HydroCAD installation folder. This establishes familiar TR-20 units, such as Tc values in hours and areas in square-miles.

A routing diagram is automatically created, with outflow routing inferred from the Standard Control statements in the TR-20 job. Each node is assigned a name based on the TR-20 cross-section or structure number. A sequential node number is also assigned to each node.

What data is converted?

Most TR-20 features are automatically imported, as listed below. If certain elements cannot be imported, a warning message will appear and the skipped items are added to the Project|Notes screen.

XSECTN - Defines cross-section data for use by REACH statements. The "zero damage" elevation is used to define the flood elevation in HydroCAD.

STRUCT - Defines stage-storage and stage-discharge data for use by RESVOR statements. (If the first storage value is greater than zero, a zero-storage stage is automatically inserted one foot lower, and the starting elevation is set to the original storage.)

DIMHYD - Defines a custom unit hydrograph. The data is stored in a separate UH file based on the project file name. If this statement is omitted, the standard SCS UH is automatically used. You can select, view, and compare UH tables on the Unit Hydrograph tab of the Settings|Calculation screen.

RAINFL - Defines a custom rainfall table. For each RAINFL statement, HydroCAD creates a separate rainfall file for use by the project. (The Runoff option is not automatically converted.) Standard SCS rainfall tables numbered 1-6 are built into HydroCAD and do not have to be defined with RAINFL statements. You can select, view, and compare rainfall tables on the Rainfall tab of the Settings|Calculation screen.

RUNOFF - Creates a subcatchment with the specified data. A runoff hydrograph is generated according to the options on the Settings|Calculation screen.  Runoff results are generally with a few percent of the 1982 TR-20 release, which is the benchmark used for HydroCAD.

RESVOR - Creates a pond with the specified STRUCT data and starting elevation. The pond routing calculation will be preformed according to the options on the Settings|Calculation screen.  Pond routing results can be expected to closely match TR-20.

REACH - Creates a reach with the specified XSECTN data and length. (XSECTN data is required, since the x and m coefficients are not supported.) The reach routing calculation will be performed according to the options on the Settings|Calculation screen.  Since HydroCAD and TR-20 employ different reach routing procedures, some differences can be expected in these calculations.

ADDHYD - Causes the specified hydrographs to be added together by routing them to a common node. When routing calculations are performed, multiple inflows are summed automatically. (After the ADDHYD statement, the input hydrograph locations are no longer available.)

SAVMOV - Reassigns the number for a specified hydrograph. The result is reflected in the routing diagram that is created during the import process. (After the SAVMOV statement, the input hydrograph location is no longer available.)

DIVERT - For diversion procedure #1, a link is created with the specified flow threshold. For procedure #2, a zero-storage pond is created with primary and secondary outflows determined by the specified XSECTN tables.

INCREM - Sets the main time step (dt) for subsequent COMPUT statements.

COMPUT - Defines a rainfall event with the specified values. The ending time is automatically set to generate 400 time steps. When multiple COMPUT statements are present, you can use the event selector to choose the active event. (Each rainfall event is applied to the entire project, regardless of the structure or cross-section range specified in the COMPUT statement.)

READHD - Creates a manual link with the specified tabular hydrograph. Since READHD statements occur after all standard control statements, the link outflow must be manually routed to the intended point in the drainage system. Any baseflow value is ignored.

BASEFLO - Due to the sequence of the TR-20 data, BASEFLO statements are not automatically converted. However, a constant base flow can be readily specified for any reach or pond, and a link can be used to introduce a triangular base flow.

INSERT, ALTER, DELETE - These statements are used to define alternative drainage scenarios (such as existing and proposed conditions), and are not automatically converted.  Instead, you should build and import a separate TR-20 file for each alternative.

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