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-HY10 OCTOBER 1973 OCTOBER 1973 v = kinematic viscosity of water; mass density of water, in slugs per cubic foot; submerged mass density; critical tractive force, in pounds per square foot; -'".''' dimensionless critical shear stress; 'tJ" tractive force, in pounds per square foot; <-fa dimensionless bed shear stress; )1 angle of repose; ,;~ angle subtended by successive tapping points to center of cylinde;:' and -,- coefficient of White's equation allowing for eccentricity. JOURNAL OF THE HYDRAULICS DIVISION p p' T, T' , To T' o cr .y INCIPIENT MOTION AND SEDIMENT TRANSPORT By Chih Ted Yang, I A. M. ASCE " .;trn.ooucnoN i l I l I ~ I Most sediment transport equations are derived under the assumption that --6crc is always a determinate relationship, at least statistically speaking, between .,tcdimentdischarge and a dominant independent variable, such as water discharge, :~ewcrage water velocity, energy slope. or shear stress. A study of all reliable ,~;""avai1abte to the writer (40) raises doubts as to the existence of the uniqueness '~.huch functional relationships. These relationships exist only under some special . conditions, and should not be accepted as being the general rule. A massive ~~ analysis (40) reveals that the unit stream power is the dominant factor '< Ie the determination of total sediment concentration. Because of the importance of unit stream power to the study of sediment >:ransport, the concept of unit stream power is further explored in this paper. ~'$pecial attention is given to the problem of incipient motion, and the possibility 5,,'ff obtaining a dimensionless equation that can be used to predict the total ~diment concentration for a given sediment and flow condition. This study is limited to noncohesive natural sand with a median sieve diameter ~.l/letween 0.062 mm and 2 mm, a specific gravity of 2.65, and a shape factor }tl about 0.7, transported by 'Yater in an alluvial channel under equilibrium ;:_tonditions. It is assumed that the energy slope can be approximated by water _'1IUface slope. Laboratory and field data collected by different investigators ;-~M'e used to verify the proposed theories. , Sote.-Discussion open until March 1, 1974. To extend the closing date one month, .. trriuen request must be filed with the Editor of Technical Publications. ASCE. This . fllptr is part of the copyrighted Journal of the Hydraulics Division, Proceedings of the ".bxrican Society of Civil Engineers, Vol. 99, No. HYIO, October, 1973. Manuscript ~.u submitted for review for possible publication on March 29, 1973. 'Assoc. Professional Sci., Illinois State Water Survey, and Water Resources Center ',.~dUniv. of Illinois, Urbana, Ill. , ,I ..I ,1 ! 1679 ;fl ,4lI