An additional feature that has been added to HEC-RAS to help user's find model stability problems, is the "Computational Level Output" option. When performing an unsteady flow analysis the user can optionally turn on the ability to view output at the computation interval level. This is accomplished by checking the box labeled Computation Level Output on the Unsteady Flow Analysis window (In the Computations Settings area on the window). When this option is selected an additional binary file containing output at the computation interval is written out. Users can control what output is written to this file from the options called Output Options. There is a tab labeled "Computation Level Output Options" on this window that allows you to control what gets written to this file, and there is also a time window option for controlling the time period for writing this data. After the simulation the user can view computation level output by selecting either Unsteady Flow Spatial Plot or Unsteady Flow Time Series Plot from the View menu of the main HEC-RAS window.
Visualization of computation level output can be accomplished with either Spatial Plots or Time Series Plots. From the Spatial Plots the user can view either a profile plot, a spatial plot of the schematic, or tabular output. The user can select from a limited list of variables that are available at the computation level output. These are water surface elevation (XS WSEl); Flow (XS Flow); computed maximum error in the water surface elevation (XS WSEL ERROR); computed maximum error in the flow (XS FLOW ERROR); and maximum depth of water in the channel (DEPTH). Each of the plots can be animated in time by using the video player buttons at the top right of the window. This type of output can often be very useful in debugging problems within an unsteady flow run. Especially plotting the water surface error and animating it in time. An example of the computational level output spatial plot is shown in Figure 7-53.

Figure 7 53. Example Spatial Plot from Computational Level Output.
The other type of plot available at the computation interval output level is the Unsteady Flow Time Series Plot. When this option is selected the user will get a plot as shown in the Figure above. Some of the same options and variables are available for the Time Series Plots as were available for the Spatial Plots.
Once a location of an instability is determined on the profile plot, or the computational spatial plot, the cross section plot can be used to further investigate the cause of the instability. The cross section plot will show isolated problems such as incorrectly placed bank stations, poor n-values, and bad station-elevation data. In addition, scrolling through its neighboring cross sections can give you an idea of transition problems like contractions and expansions that occur to abruptly, poorly defined ineffective flow areas, or incorrectly handled levees or natural high ground spots.