This table allows the user to turn the Preissmann slot option on or off for any or all of the cross sections that have lids added to them. An example of this table is shown below in Figure 5-77. Figure 577. Table Editor for Preissmann Slot Option.
As shown in the Figure above, every cross section that has a lid will show up in the table. If the user wants the Preissmann slot option to be used during unsteady flow calculations, then that cross section must be checked in the column labeled Add Preissmann Slot. An easy way to turn this option on or off for all of the cross sections is to click on the column heading of the check box column (which will highlight all of the locations in the table). Then, pressing the space bar will toggle the check mark on and off for all of the highlighted locations.
The Preissmann Slot option will instruct the computational code to treat this cross section and lid as a pressurized pipe. This option is only for unsteady flow computations. If the option is turned on, the conveyance curves for the cross section will be truncated at the maximum low chord elevation of the lid. Preissmann slot theory will be used for modeling the flow once it becomes pressurized. For more on modeling pressurized pipes in HEC-RAS, please review the section on modeling pressurized pipes in Chapter 16 of this manual, as well as the HEC-RAS Hydraulic Reference manual.
