ABSTRACT. 



11 



sary to postulate constancy in some accessory 

 condition. If slope be the constant, in which 

 case velocity changes with discharge, capacity 

 varies on the average with the 3.2 power of 

 velocity. If discharge be the constant, in 

 which case velocity changes with slope, capacity 

 varies on the average with the 4.0 power of 

 velocity. If depth be the constant, in which 

 case velocity changes with simultaneous 

 changes of slope and discharge, capacity varies 

 on the average with the 3.7 power of velocity. 

 The power expressing the sensitiveness of 

 capacity to changes of mean velocity has in 

 each case a wide range of values, being greater 

 as slope, discharge, and fineness are less. 



Mixtures. In general, debris composed of 

 particles of a single size is moved less freely 

 than debris containing particles of many sizes. 

 If fine material be added to coarse, not only is 

 the total load increased but a greater quantity 

 of the coarse material is carried. 



Modes of transportation; movement of par- 

 ticles. Some particles of the bed load slide; 

 many roll; the multitude make short skips or 

 leaps, the process being called saltation. Sal- 

 tation grades into suspension. When particles 

 of many sizes are moved together the larger 

 ones are rolled. 



Modes of transportation; collective move- 

 ment. When the conditions are such that the 

 bed load is small, the bed is molded into hills, 

 called dunes, which travel downstream. Their 

 mode of advance is like that of eolian dunes, 

 the current eroding their upstream faces and 

 depositing the eroded material on the down- 

 stream faces. With any progressive change of 

 conditions tending to increase the load, the 

 dunes eventually disappear and the de'bris sur- 

 face becomes smooth. The smooth phase is in 

 turn succeeded by a second rhythmic phase, in 

 which a system of hills travel upstream. These 

 are called antidunes, and their movement is 

 accomplished by erosion on the downstream 

 face and deposition on the upstream face. 

 Both rhythms of de'bris movement are initiated 

 by rhythms of water movement. 



Application of formulas. While the prin- 

 ciples discovered in the laboratory are neces- 

 sarily involved in the work of rivers, the labo- 

 ratory formulas are not immediately available 

 for the discussion of river problems. Being 

 both empiric and complex, they will not bear 



extensive extrapolation. Under some circum- 

 stances they may be used to compare the work 

 of one stream with that of another stream of 

 the same type, but they do not permit an esti- 

 mate of a river's capacity to be based on the 

 determined capacities of laboratory streams. 

 The investigation made an advance in the 

 direction of its primary goal, but the goal was 

 not reached. 



Load versus energy. The energy of a stream 

 is measured by the product of its discharge 

 (mass per unit tune), its slope, and the accel- 

 eration of gravity. In a stream without load 

 the energy is expended in flow resistances, 

 which are greater as velocity and viscosity are 

 greater. Load, including that carried in sus- 

 pension and that dragged along the bed, affects 

 the energy in three ways. (1) It adds its mass 

 to the mass of the water and increases the 

 stock of energy pro rata. (2) Its transporta- 

 tion involves mechanical work, and that work 

 is at the expense of the stream's energy. (3) 

 Its presence restricts the mobility of the water, 

 in effect increasing its viscosity, and thus con- 

 sumes energy. For the finest elements of load 

 the third factor is more important than the 

 second; for coarser elements the second is the 

 more important. For each element the second 

 and third together exceed the first, so that the 

 net result is a tax on the stream's energy. 

 Each element of load, by drawing on the supply 

 of energy, reduces velocity and thus reduces 

 capacity for all parts of the load. This prin- 

 ciple affords a condition by which total capacity 

 is limited. Subject to this condition a stream's 

 load at any time is determined by the supply 

 of de'bris and the fineness of the available 

 kinds. 



Flume transportation. In the experiments 

 described above experiments illustrating 

 stream transportation the load traversed a 

 plastic bed composed of its own material. 

 Other experiments were arranged in which the 

 load traversed a rigid bed, the bottom of a 

 flume. Capacities are notably larger for flume 

 transportation than for stream transportation, 

 and their laws of variation are different. 

 Rolling is an important mode of progression. 

 For rolled particles the capacity increases with 

 coarseness, for leaping particles with fineness. 

 Capacity increases with slope and usually with 

 discharge also, but the rates of increase are less 



