Exporting a HEC-1 Hydrograph for HEC-RAS Unsteady Flow

We are going to export a HEC-1 hydrograph to a DSS file to use in HEC-RAS unsteady flow modeling.  This will be useful for us to do 2D flow modeling in HEC-RAS


1. Your HEC-1 model must have a start date and time and your HEC-1 model computation interval must be a standard DSS time interval ("Time series data is always written at the interval specified on the IT record. Consequently, if a ZW record is used to write time series data, then the computation interval on the IT record must be a standard DSS time interval." "Must be a standard DSS time interval; 5MIN, 10MIN, 15MIN, 30MIN, 1HOUR, 2HOUR, 3HOUR, 4HOUR, 6HOUR, 1DAY")
IT    15 01JAN01    0000     300

2.  You must insert a ZW record after the KK record for the hydrograph you want to export and before the next KK record, and it is orderly to always put the ZW record as the last line before the next KK record.

3.  The ZW record is free format and uses spaces and = signs as delimiters:
ZW A=PROJECT B=ID (HYDROGRAPH OPERATION NAME FROM KK RECORD) C="FLOW"/"STAGE"/"ELEV" F=ADDITIONAL_NOTE(eg. 100-YR)

Here is an example to export the flow hydrograph operation called C521 from the file MAPLE100.dat:
ZW A=MAPLE CREEK B=C521 C=FLOW F=100-YR

4. You must specify the DSS file name when you run HEC-1
"C:\fcdmc\st\Models\HEC1.exe" INPUT=harw100.dat OUTPUT=harw100.out DSS=harw100.dss

Unrelated HEC-RAS tips about Stabilizing Unsteady Flow

1.  Zero flows are bad.  Try cutting off the ends of your hydrograph.
2.  Small computation intervals are good.
3.  Adjust your HTAB parameters (left side toolbar under Geometric Data) so that HEC-RAS makes finer resolution hydraulic tables for every cross section.  See Tuesday Tip of the Week–HTAB Headwater Maximum for Bridges