1D river simulations - backward compatibility tab

Updated on 05 Aug 2022
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These options are utilised when you need to re-run an old model under the exact same conditions as the original simulations (which have used an older version of the 1D solver).

A number of updates to the calculation engines included in the recent versions to enhance performance or address known bugs will mean that using the latest version to re-run an old model may yield different results. In some cases it may be desirable to retain the older functionality, e.g. where calibrations have worked around problems to account for their inclusion. Thus a series of 'backward compatibility' options have been included in Flood Modeller to enable modellers to 'rollback' selected updates to their previous state and then incorporate these changes in subsequent simulations. The 'rollback' options are detailed in the table below:

Option	Description
Logical rules math library	Enables functions such as MABS (absolute value), SQRT, SIN, etc to be used in rules functions (from v2.4).
Solve dh=0 for reservoirs at start time	Option that can prevent the adding of spurious volume for spilling reservoirs on initial timestep (from v2.4).
Use correct perimeter for Preissmann slot	Corrects an error in calculating the perimeter for the automated Preissmann slot (from v2.4).
Evaluate rules at t0	Option to evaluate rules on the initial timestep (time zero). The default in v2.5 was false.
Evaluate rules on first iteration	Evaluate rules defined in the model based on conditions at the first iteration (the alternative is after the last iteration. The default in v2.5 was for this option to active.
Reset sample count after position instruction	This option should always be set to true, but in v2.5 it was set to false.
Constrain d/s FPS area correctly	This is a bug fix for floodplain sections (FPS) that was available from v3.0 and later. The old behaviour can be retained using this option to enable backwards compatibility with older models.
Use flow from culvert outlet node	Versions up to v3.4 used the combination of culvert flow and area of remote node (i.e. node receiving culvert outflow such as river section) to calculate culvert outlet velocity. This could be inaccurate as the remote node area could be affected by multiple culverts (or other inflows). In v3.5 this was improved to use the velocity calculated for the remote node (e.g. river flow / river cross section area). Leave this option unchecked to apply the previous methodology for back compatibility.
1D Engine Version	Default setting is 'current version' but can be rolled back to previous versions to maintain back compatibility with recent simulations. Alternatively, you can run the double precision version. This may reduce performance, but may be required to obtain a correct solution, e.g. large area reservoirs at high elevations running in a small timestep model may require the double precision version to compute small changes in water level (that may otherwise register as no change).
Direct Method iterations	These settings used to be fixed. They can now be adjusted to help users maintain back compatibility. In more recent versions the default settings have been changed and so using these it may not be possible to recreate old runs. Hence settings can be adjusted, e.g. max. iterations default previously was 20. However, it is thought that these settings will have a negligible affect and so can usually be left as current defaults.
Use Defaults from version	Provides option to revert all default settings to those used in an earlier version of Flood Modeller. Default (i.e. do nothing) setting is to use current version defaults – this option will not write anything to your ief file.

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1D river simulations - updating tab