Checking conveyance plots with ISIS v3.1
Why do I need to do this?
If the conveyance does not monotonically increase with depth within a cross section, this can lead to model instabilities,
What causes such irregularities?
Usually this is caused by a relatively large increase in wetted perimeter, compared with the increase in wetted area for a small increase in water level. Typically this will be as the water goes out-of-bank. Incorrect section data can also cause problems.
How can I tell before running a simulation?
With the new conveyance plotting facility in ISIS v3.1, one can overlay the conveyance curve on a cross section plot - this gives an instant relationship between the cross section and conveyance. Any irregularities in conveyance can be matched to a section elevation point.
To display this, first plot a RIVER cross section. Then right click and select "Edit Series" (or use the Ctrl-D shortcut). Tick the Conveyance check box to display the conveyance curve on the cross section.
Note: You can also display the conveyance curve for the section immediately upstream and/or downstream on the same plot (if such sections exist).
Alternatively, you can select the "Tabulate Cross-Section Properties" option from the Tools menu to display Conveyance and other cross section properties in tabular or graphical form for one or any number of selected cross sections.
What can I do to prevent decreasing conveyance?
By inserting panel markers at the bank top, this compartmentalises the conveyance. The conveyance for each panel, delimited by panel markers, will be calculated separately, and then added together to give a total conveyance for the section. By separating out any sudden changes in geometry from the main channel section, this minimises the chances of decreasing conveyance occurring.
If the conveyance does not monotonically increase with depth within a cross section, this can lead to model instabilities,
What causes such irregularities?
Usually this is caused by a relatively large increase in wetted perimeter, compared with the increase in wetted area for a small increase in water level. Typically this will be as the water goes out-of-bank. Incorrect section data can also cause problems.
How can I tell before running a simulation?
With the new conveyance plotting facility in ISIS v3.1, one can overlay the conveyance curve on a cross section plot - this gives an instant relationship between the cross section and conveyance. Any irregularities in conveyance can be matched to a section elevation point.
To display this, first plot a RIVER cross section. Then right click and select "Edit Series" (or use the Ctrl-D shortcut). Tick the Conveyance check box to display the conveyance curve on the cross section.
Note: You can also display the conveyance curve for the section immediately upstream and/or downstream on the same plot (if such sections exist).
Alternatively, you can select the "Tabulate Cross-Section Properties" option from the Tools menu to display Conveyance and other cross section properties in tabular or graphical form for one or any number of selected cross sections.
What can I do to prevent decreasing conveyance?
By inserting panel markers at the bank top, this compartmentalises the conveyance. The conveyance for each panel, delimited by panel markers, will be calculated separately, and then added together to give a total conveyance for the section. By separating out any sudden changes in geometry from the main channel section, this minimises the chances of decreasing conveyance occurring.
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