Research Of Movable-bed Resistance And Hydraulic Geometry In Alluvial Channels Based On Extreme Hypotheses

The extreme hypotheses is common law followed the self-adjusting mechanism of alluvial channels in riverbed evolution presently. So far, there have been many extreme hypotheses to be put forward and to be used to explain the self-adjusting of alluvial channels. Hydraulic geometry and movable-bed resistance are staple of alluvial channels, so this paper uses extreme hypotheses to study hydraulic geometry and movable- bed resistance in alluvial channels. Primary contents of research are as follows:1. Compare and analysis of the extreme hypotheses. In this paper , source and basic relations of the extreme hypotheses are compared and analyzed, and their shortages and correlation of the extreme hypotheses are found. Based on the extreme hypotheses, common models of hydraulic geometry and movable-bed resistance are established.2., The research of stable channel shape on the condition of bedload discharge equals zero by use the extreme hypotheses. Based on the principle of minimum stream power, a model of functional extreme of stable channel shape is established, and it is derived that the shape of stable channel is a circular curve by use of calculus of variation. This circular curve shape is actually the extension of the hydraulic optimum section in hydraulics to the situation of considering ban stability. Combined with resistance equation of channel and critical incipient shear stress, the method of designing hydraulic geometry of stable channel is set up in this paper. It is shown that present model approximates to the model of Diplas and Vigilar. Also the hydraulic geometry of stable channel proposed by this paper agrees well with measured data.3. Perfection and betterment of the extreme hypotheses on the problem of hydraulic geometry. Based on the model of hydraulic geometry established by this paper, hydraulic geometry on the condition of various bedload discharges (including the condition that bedload discharge equals zero) is educed by use of maximum sediment transporting capacity and minimum stream power separately. Also the hydraulic geometry proposed by this paper agrees well with measured data and can be used for the calculation of actual problem.4. Perfection and betterment of the extreme hypotheses on the problem of...