A comprehensive list of pipe coefficients of friction for the Hazen-Williams and Manning formulae derived from the Darcy-Weisbach formula and Colebrook-White transition law for roughness values (k) A comprehensive list of pipe coefficients of friction for the Hazen-Williams and Manning formulae derived from the Darcy-Weisbach formula and Colebrook-White transition law for roughness values (k) Posted in .