NEW IN RESSIM 3.5

ResSim Variants were added to ResSim 3.4 and 3.5 to improve the ability to distinguish between inputs for a ResSim alternative in standalone compute and inputs used by a ResSim alternative being computed as part of a sequence of models, such as in CWMS CAVI or HEC-WAT.   ResSim Variants allow for variations of an alternative for use with standalone (default) and use with different program orders in CAVI and HEC-WAT, preserving the other aspects of the alternative.


ResSim Variants Definition

ResSim Variants are, very simply, different versions of the input time series information (known flows and lookback time series) used by an alternative, that can be selected when the model is being run in a CAVI or HEC-WAT compute environment.

Background

ResSim alternatives typically match a series of conditions in the model that define how the simulation should be performed - including (but not limited to) the timestep of the model, the input timeseries (boundary conditions), lookback values (initial conditions) and which operations sets each reservoir should use.  When these alternatives were used in HEC-WAT and CWMS CAVI modeling, those programs would overwrite the timeseries with their own "model linking" information, specifying prior models (such as HEC-HMS or the HEC-WAT Hydrologic Sampler) that provide inputs to the ResSim model.  As a work-around, users would create copies of the alternative for each set of inputs to be used, but this workaround then required updating all copies of that alternative when some other detail was changed.  This created additional work and steps to review with some changes to the model. Variants were introduced as a way to map multiple input combinations to the same alternatives, eliminating the need for this duplication.

How Variants Work

HEC-ResSim creates a separate set of files for each of the variants that are required.  By default, a set of these files are created for the "ResSim-Default" variant, which is the variant used during standalone computes.  For software where ResSim runs as a compute plugin, such as the CWMS CAVI and HEC-WAT, the HEC-ResSim plugin for those programs uses a detail of those computes to create additional variants. 

In HEC-ResSim 3.5, the plugins for the CWMS CAVI and HEC-WAT will use the program order name to define the additional variant names.  For example, if a CWMS CAVI watershed has two program orders, one starting with ResSim called "ResSimOnly" and one starting with HMS and then running ResSim called "HMS+ResSim", both of these will get their own variants.  Thus, if ResSim is being used with an external forecast in the CAVI, the input model linking for that forecast will be kept separate from the input data from the input data linking for the compute that uses HMS. For more information regarding the program order in CWMS, view the Program Order, CWMS users manual page. For the HEC-WAT, view the Program Order user manual page.

In a future version of CWMS CAVI and HEC-WAT, the required number of variants will be reduced to one for each program, and input linking will be provided by CAVI or HEC-WAT at compute time.  This will allow each simulation to have different model linking, and will work with other software, including HEC-HMS and HEC-RAS.  Existing variants will not be eliminated unless the user chooses to delete them.

Behind the scenes: the `.fits` files

HEC-ResSim stores the DSS filename and pathnames of the selected input time series in a series of files extension of .fits.  Each variant creates a copy of this file (and other required files) in the watershed's /rss/  directory, with the variant name added after the alternative name.  Other features that support variants, such as global variables, generate their own copies of their files, using a similar naming convention.  The one exception is that observed data does not support variants, but will create a file ending in Obs.fits, which contains the observed data time series pathnames.

Here is an example of a variant tabs for a ResSim alternative called “GC Only” that is used in a CWMS forecast run using a program order named “PO1”.

The ResSim Alternative Editor displays the ResSim-Default and variant tab, CWMS-PO1. The example alternative name

Note: Observed data does not currently get revised due to model linking so there is currently no variant subtabs implemented for observed data tab. KNOWN LIMITATION

How to View the Variants of an Alternative

When accessing the model though the HEC-ResSim user interface, a set of tabs for each variant may be presented to the user on the Time-Series and Global Variable tabs.  This additional row of tabs can be used to see all of the variants that have been set up for this model.  These additional variants are created when the HEC-ResSim plugin for CWMS CAVI or HEC-WAT access the model linking for the model, so they may not show up until the model is edited in the CAVI or HEC-WAT interface.

The view of the ResSim Variants has evolved since they were first implemented as part of CWMS 3.0.  Initially, variants were mostly hidden from view and only the variant needed in the current “context” (ResSim, CWMS, or HEC-WAT) was displayed (as the DSS pathname information) on the Time Series tab of the ResSim Alternative Editor.  For example, if you launched ResSim in standalone, you would only see the ResSim Default variant for each alternative.  However, if you launched ResSim from within the CAVI, the Time Series Tab of the Alternative editor would add a Variants menu to the Alternative Editor and would display, by default, the CWMS variant for the current context but you could view other variants by selecting them from the Variant menu.

After the release of CWMS 3.1.1, while addressing a few oversights in the implementation of variants in the CAVI's ResSim plugin and the CAVI’s Model linking editor, the display of the variants was made more visible.  As of CWMS 3.2.1 and ResSim 3.5, if any ResSim alternative has at least one variant, the variants are shown on subtabs of the Time Series tab in the ResSim Alternative Editor, whether ResSim is launched in standalone or from the CAVI or WAT. Each Time Series subtab displays the name of the variant as the tab label.  When possible, the current context (such as a CAVI forecast or HEC-WAT simulation) will cause the ResSim editor in those programs to select the relevant variant for that context.