274 



SCIENCE. 



[X. S. Vol. XX. No. 504. 



years so well defended by revetments that 

 the course has here remained practically 

 unchanged for thirteen years. It is above 

 this point, in that part of the river 's course 

 which has not been so completely re- 

 strained artificially, that significant results 

 must be looked for. Before presenting the 

 results of my map studies, it is desirable to 

 explain certain terms as illustrated in 

 Fig. 1. 



By 'bend' (Fig. 1, B) in a river channel 

 is meant a curve whose lateral changes in- 

 volve a decrease of radius; by 'meander' 

 (Fig. 1, A) a. curve whose lateral changes 

 involve a steady increase of radius until a 

 cut-off occurs or changes elsewhere in the 

 channel induce a disturbance here. • This 

 distinction grew out of the difference in 

 kinds and amounts of cutting at the two 

 sets of curves. It is evident from an exam- 

 ination of the maps and the generalized 

 conditions represented in Fig. 1 that as 

 meanders develop, the relatively straight 

 stretches in the river's course will be con- 

 tinuously shortened and there will be a 

 corresponding increase in the length of 

 that part of the course included within the 

 meanders. As this change progresses the 

 radius of curvature is reduced from in- 

 finity to a finite quantity, the reduction 



continuing until the neck is as small as any 

 other part of the lobe. From this time on 

 the same tendency which ultimately pro- 

 duces a cut-off between alternate meanders 

 operates to the enlargement of the radius 

 of curvature, not only throughout the 

 meander between them, but at the place 

 where a cut-off occurs as well. The ox- 

 bow lakes have for this reason a longer 

 average radius of curvature than an equal 

 number of present meanders. The reaches 

 (Fig. 1, C) include those wavering parts 

 of the river's course the further develop- 

 ment of which can not be accurately fore- 

 told, although it can be shown that the 

 reaches usually develop into bends and the 

 bends grow into meanders. It is in the 

 reaches that there is the greatest difficulty 

 of navigation, islands and bars occurring 

 irregularly, for, lacking a dominant tend- 

 ency, the energies of the stream are not 

 bent in a relatively permanent and definite 

 direction which would result in a pai't of 

 the channel being maintained at a somewhat 

 constant depth, as is the case where in con- 

 sequence of the development of bends and 

 meanders, the threads of the stream pursue 

 a less erratic course. 



The following tables contain a detailed 

 list of areas of lateral cutting expressed 



TABLE I. 



Classified Measuhements of Areas Cut on the Eight Side and on the Left Expressed in 

 250THS OP A Sq. M. Sheets 13 to 17 Inclusive. 



