A review of empirical equations for estimating stream roughness and their application to four streams in Victoria

Abstract

Measured Manning’s n values at four sites in Victoria, Australia, the Acheron River at Taggerty, the Merrimans Creek at Stradbroke West, the Mitta Mitta River at Hinnomunjie Bridge and the Tambo River downstream of Ramrod Creek were compared to n values given by empirical equations found in the literature. For the Merrimans Creek, the empirical equations underestimated the measured n values for all discharges. For the Mitta Mitta and Tambo Rivers, equations suggested by Dingman and Sharma1 and Riggs2 provided good estimates of n.Where information on substrate size was used equations suggested by Limerinos3, Froehlich (in Coon4), Bray (1979, in Phillips and Ingersoll5) and Griffiths6 provided reasonable estimates of n for some discharges for the Acheron River and Mitta Mitta River, but these same equations did not perform well for the Tambo River.The procedure suggested by Stewardson7,8 for predicting Manning’s n at a range of discharges, given one measured value of n at a known discharge, was also tested. It was found that this approach, although based on a large international data set7,8 was not useful for these streams. In fact, Manning’s n values showed little variation with discharge.