Posted in Web Guide for Selecting Manning’s Roughness Coefficients for … October 9, 2021 6-20. Photographs showing flood plains having verified n values: 6. Cypress Creek near Downsville, La., Vegrf=0.0067 13 7. Bayou de Loutre near Farmerville, La., Vegd=0.0061 14 https://pubs.usgs.gov/wsp/2339/report.pdf