HEC-EFM can import time series data that are stored in the Hierarchical Data Format (HDF) for use as flow regimes.  HDF is a frequently used database format (http://www.hdfgroup.org/) and is employed by at least two HEC software to store model simulation outputs (HEC-RAS for two-dimensional unsteady flow output and HEC-EFMSim for two-dimensional ecological simulation output).  Through the “Edit – Flow Regimes – Batch add from HDF…” menu option, users specify input HDF files, dates and times of data being imported, data tables and key aspects of their structure and content, and a naming convention for the flow regime.  Resulting flow regimes are compound in the sense that a single flow regime identifier contains multiple sets of concurrent time series (or time series and paired data).  For example, the first flow regime in Figure 65, entitled “Wetland Restoration Zone”, has data that would comprise 2,940 traditional HEC-EFM flow regimes and is one of the four listed that together have more than 32,000 parts.  Each part is computed independently for all active relationships.  Users should consider style sheet choice and output settings before applying HEC-EFM for large compound flow regimes.

Figure 65.  Importing HDF data for use in HEC-EFM.  Structure and content of an HEC-RAS 2D output file is at back, “Batch add from HDF…” interface to right, and Flow regimes list at bottom.


The data and mathematical process HEC-EFM uses to analyze compound flow regimes is the same as for traditional flow regimes with one exception.  Use of time series from HDF are supported for a wide range of time steps (19 increments ranging from 1 minute to 1 day) whereas only daily time series may be used in traditional flow regimes.  During conversion from subdaily to daily, users may specify which daily time series is of interest: means, minimums, or maximums.  HEC-EFM also provides a setting for the user to declare whether data from HDF are instantaneous or period average values, which affects the conversion to daily values.  Apart from dealing with subdaily time steps, the process is unchanged.  Data for each flow regime are queried per the season, duration, rate of change, and percent exceedance parameters for each relationship.  Results are written and reported per output settings controlled by the user.  Flow regime names are recorded as “Identifier-suffix” for compound flow regimes.

As with traditional flow regimes, subsequent recalculations simply repeat the whole process.  Subdaily data are converted to daily, queried per relationship parameters, and then results are written and reported.  To save time, HEC-EFM offers a menu option “Preprocess from HDF file…” that converts subdaily data to daily and saves the daily results in a new HDF table (Figure 66).  An associated time/date table is also generated.  The number of time series is unchanged; all time series are processed.  The resulting HDF file can then be used via the Batch Add Flow Regimes from HDF interface as in Figure 65.  Preprocessing has been shown to reduce overall compute times by approximately one third.  

Figure 66.  Avoid repetitive and time consuming conversions from subdaily to daily time steps via the Preprocess Data from HDF feature.  With this, subdaily data are converted and written as daily values to a new HDF file that can then be used as input for flow regimes in HEC-EFM.