Determination of friction factor for corrugated drains

This paper describes two approaches for evaluating the resistance factor of corrugated drains. The first employs a monomial formula and is based on dimensional analysis while the second uses a physically-based formula that incorporates the relationships among hydraulic parameters measured for a set of corrugated pipes. The latter depends on an evolutionary modelling technique that renders a superior description of the hydraulics of the tested corrugated pipes, outperforming the classical monomial formula for rough pipes. The formulae derived herein accurately reproduce experimental data and highlight the influence of dimensionless factors on roughness values. Three differently sized corrugated plastic pipes with slopes ranging be-tween 3.50 and 17.50% were considered. The tests were directed at measuring open channel flow hydraulic parameters in order to ascertain the role of friction factors when wake-interference occurs. This hydrodynamic phenomenon, observed in the tested pipes, is situated in the rough fully turbulent flow region of the Moody diagram. From a technical standpoint, wake-interference is interesting because the abnormal turbulence experienced along the channel’s wall-roughness elements generates additional energy dissipation, entailing potentially significant implications for sewer networks installed on steep slopes.