An Experimental Study of the Effect of Boundary Roughness in Rectangular Open Channels

In order to precise design, the determination of flow behavior in open channels have always been subjected by the hydraulic researchers. The traditional Manning-Strickler, Keulegan, and Colebrook-White equations provide inaccurate estimations for resistance coefficients in roughened rectangular channels. In this research, flow resistance coefficients both in smooth and rough rectangular channel sections were investigated by using experimental models and three types of river materials. The results show that the revised Strickler formula estimates Manning's n with an average error about 2.56%; and the revised Keulegan equation for smooth and Colebrook-White equation for roughened channels give some good agreements with the experimental measurements by an error of less than 4.91% and a correlation coefficient of 0.983. Some empirical derived equations are also presented which gives the value of Nikuradse sand equivalent roughness, ks, as a function of roughness diameter size. A new explicit formula presented for friction factor, f, using gene expression programming (GEP) for uniformly roughened rectangular channels with an average relative error 5.1% and the corresponding correlation coefficient, 0.981.