طراحی کانالهای پایدار در بستر شنی

Over the past decades, numerous regime formulations, describing channel width, average flow depth and channel slope, have been proposed for gravel-bed rivers. Using the downstream hydraulic geometry measurements from 280 field channels, nine gravel-bed predictive formulations were compared. They are attributed to Bray, Chang, Hey and Thorne, Kellerhals, Neil, Parker and Simons, and Albertson. The comparison showed that the dominant discharge and the median grain size are not sufficient hydraulic variables to predict the channel geometry (width, depth, and especially channel slope). Seeking more complex formulations with the measured parameters, it was not possible to improve the existing formulations significantly without spurious influences of common variables. A second database is thus gathered from 19 laboratory-based boundary-layer measurements published in Kironoto and Graf (13) and Song et al. (19). In fact, the boundary-layer theory will respond to a fundamental question: are the existing available variables in literature not sufficient or the methods of their estimations are not appropriate? Based on the present study, the methods of their estimations should be changed. The second database allows proving the usefulness of the Shields parameter for the prediction of average flow depth and channel slope. Hence, using boundary-layer theory for prediction of Shields parameter and stable channel parameters is recommended.