Default Manning's N and Range Grasses

[Justin Goldstein]

Colleagues,
  Does anyone know the reasoning behind why  the default values for Ch_N1 and Ch_N2 in SWAT are 0.014?  Also, does anyone know which grasses are represented by the "range-grasses" land use class?  My watershed contains mostly native C4 grasses (little bluestem, blue grama, buffalo grass) which were identified by both the Crop Dataset Layer (CLD) and the NLCD as "range-grasses", but I just wish to confirm that SWAT's definition of "range-grasses" coincide with that in the CLD and the NLCD.  I see by looking at the SWAT crop database, for instance, that the parameters for Little Bluestem are similar to those of the "Range-Grasses" category with some exceptions in OV_N and CN2, but am just looking to confirm that that the "range-grasses" category in SWAT was designed as a generic category for the different grasses in the SWAT crop database.

  Thanks so much.
  -Justin G.

[Danielle T]

Hey Justin,
For the Manning's N, SWAT just assigns almost a lower bound to this as
it does with most parameters. I would definitely change it based on
the type of stream you have. I found that this helped my calibration a
lot and also it is a more realistic representation of the basin flows.
Here is a good reference: http://www.fsl.orst.edu/geowater/FX3/help/8_Hydraulic_Reference/Mannings_n_Tables.htm.
Good luck

Danielle