THE TRANSPORTATION OF DEBRIS BY RUNNING WATER. 



By GROVE KARL GILBERT. 



CHAPTER I. THE OBSERVATIONS. 



INTRODUCTION. 



GENERAL CLASSIFICATION. 



Streams of water carry forward debris in 

 various ways. The simplest is that in which 

 the particles are slidden or rolled. Sliding 

 rarely takes place except where the bed of the 

 channel is smooth. Pure rolling, in which the 

 particle is continuously in contact with the 

 bed, is also of small relative importance. If 

 the bed is uneven, the particle usually does not 

 retain continuous contact but makes leaps, and 

 the process is then called saltation, an expres- 

 sive name introduced by McGee. 1 With swifter 

 current leaps are extended, and if a particle 

 thus freed from the bed be caught by an 

 ascending portion of a swirling current its 

 excursion may be indefinitely prolonged. Thus 

 borne it is said to be suspended, and the process 

 by which it is transported is called suspension. 

 There is no sharp line between saltation and 

 suspension, but the distinction is nevertheless 

 important, for it serves to delimit two methods 

 of hydraulic transportation which follow differ- 

 ent laws. In suspension the efficient factor is 

 the upward component of motion in parts of a 

 complex current. In other transportation, 

 including saltation, rolling, and sliding, the 

 efficient factor is the motion parallel with the 

 bed and close to it. This second division of 

 current transportation is called by certain 

 French engineers entrainement but has received 

 no name in English. Being in need of a suc- 

 cinct title, I translate the French designation, 

 which indicates a sweeping or dragging along, 

 by the word traction, thus classifying hydraulic 

 transportation as (1) hydraulic suspension and 

 (2) hydraulic traction. 



i McGee, W J, Oeol. Soc. America Bull., vol. 19, p. 199, 1908. 



The bed of a natural stream which carries a 

 large load of debris is composed of loose grains 

 identical in character with those transported. 

 The material of the load is derived from and 

 returned to the bed, and the surface of the bed 

 is molded by the current. When debris is 

 transported through artificial channels, such as 

 flumes and pipes, the bed is usually rigid and 

 unyielding. Trifling as this difference appears, 

 it yet occasions a marked contrast in the quan- 

 titative laws of transportation, and in the labo- 

 ratory the two kinds of transportation were the 

 subjects of separate courses of experimentation. 

 It is necessary, therefore, for present purposes, 

 to base a second classification of hydraulic 

 transportation on the nature of the bottom. 

 As the bed is typically plastic in stream chan- 

 nels and typically rigid in flumes and other 

 artificial channels, it is convenient to call the 

 two classes stream transportation and flume 

 transportation . 



The second classification traverses the first 

 and their combination gives four divisions 

 stream suspension, stream traction, flume sus- 

 pension, and flume traction. This report 

 treats of stream traction and flume traction. 

 It contains the record . and discussion of a 

 series of experiments made hi a specially 

 equipped laboratory at the University of Cali- 

 fornia, Berkeley, in the years 1907-1909. 



STREAM TRACTION. 



Previous to the Berkeley work little was 

 known of the quantitative laws of stream 

 traction. The quantity of material trans- 

 ported has sometimes been said to be propor- 

 tional to the square of the slope, but I have 

 failed to discover that the statement has a re- 

 corded basis in theory or observation. A state- 



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