: Developed based on data collected from 50 measurements on 11 gravel-bed streams in California and generally considered applicable to high in-bank flows in straight, gravel-bed channels. Both bed material sizes and relative roughness were incorporated into Limerinos's equations. It is stated in the report that the investigation was confined to channels with coarse bed materials, to be as free as possible from the flow-retarding effects that are not associated with particle size. All discharges tested had Froude numbers less than 1 to avoid the complication of bed-form roughness that is associated with the alluvial channels composed of fine bed materials.
Limerinos presented two characteristic bed-particle sizes in his analysis, d84 and dw, but allowed users to make their own choice. The weighted composite size, dw, was calculated using a weight of 0.6 for d84 , a weight of 0.3 for d50 and a weight of 0.1 for d16 . He recommended the use of dw rather than d84 because the use of d84 implies that the distribution of bed material sizes is irrelevant. If users prefer to use dw in the equation in place of d84, the constant 1.16 in the denominator needs to be replaced by 0.90.
Limerinos J T, 1970, Determination of the Manning coefficient from measured bed roughness in natural channels: US Geological Survey, Water Supply Paper 1898-B, 47 p.