Manning's N parameterization

[rogerlew]

[From Scott]

I have been looking into what Manning’s n is assigned to stream channels generated on WEPPcloud. It appears that n=0.3 is the default value assigned to all channels.

Something in the range of 0.04 – 0.08 would be a good estimate for Manning’s n in most of the streams where we work, so I plotted runs using that range of values for comparison.

The hydrographs below were generated from runs in the Black Hollow watershed which was impacted by the Cameron Peak fire. It is about 2500ha and has 60 modeled reaches. The single storm hydrographs were generated using the storm characteristics from day 11219 of the 50 year simulation.

[rogerlew]

Potential option from Scott

• Short term- use the chnbnbr value on line 12b instead of chnn on 13a in the pw0.chn input file.
• Long term- have an input similar to the CS input in the advanced WEPP Channel Input menu where this value can be determined/assigned.

[rogerlew]

[rogerlew]

https://github.com/rogerlew/wepppy/blob/master/wepppy/wepp/management/data/channels.defs

[rogerlew]

chnnbr = 0.04 is bare channel

chnn is more sensitive

chnn must be greater than chnnbr add note to advanced options

[rogerlew]