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Samir A

Storage width and Effective flow width

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Hi Samir,

Effective Flow Width differs from Storage Flow Width in that it takes into consideration the effects of varying manning's 'n' across the cross-section. Effective Flow Width is only going to be different from Storage Flow Width when considering channel types such as open channels where Manning’s n varies across the channel.

For open channels, the Effective Flow Width is used to extend the cross-section conveyance properties if the water level exceeds the highest elevation in the cross-section, and similarly, the Storage Flow Width is used to extend the surface area (storage) of the connected nodes for water levels above the top of the cross-section (providing the 1d_nwk UCS – Use Channel Storage – flag is true).  Hydraulically, cross-sections and nodal area tables are extended indefinitely on this basis.

The Depth Limit Factor’s primary role is to set the maximum depth in a channel for detecting an instability – it plays no role in the hydraulic computations. Some modellers use it for quality control to stop a simulation should the water level in a channel or node exceed the highest elevation in the channel cross-section or nodal area table by triggering a forced instability.  This is done by specifying “Depth Limit Factor == 1” and is useful if the modeller wants to make sure that the calculated water levels never exceed the data input for cross-sections and any nodal area tables.  If it does exceed then this would indicate the need to obtain/extract/extend the data for the exceeded locations.

Please read Section 5.10 and Appendix B page 6 - 7 of the 2016 TUFLOW manual for more details. 

Thanks, Ellis

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