ON KIYERS AND ESTUARIES. 555 



On Certain Laws relating to the Regime of Rivers and Estuaries, 

 and on the Possibility of Experiments on a small scale. By 

 Professor Osborne Reynolds, F.R.S. 



[A communication ordered by the General Committee to be printed in extenso 

 among the Reports.] 



1. The object of tKis communication is to bring before Section G certain 

 results and conclusions with respect to the action of water to arrange 

 loose o-ranular material over which it may be flowing. These results and 

 conclusions were in the first instance arrived at during a long-continued 

 investigation, undertaken with a view to bring the general theory of 

 hydrodynamics into accord with experience, rather than with any special 

 reference to the subject in hand, but have since been to some extent made 

 the subject of special investigation. 



2. A systematic study of the regime of rivers naturally divides itself 

 under three heads, which may be stated as follows : — 



(1.) The more general facts observed as regards the regimen of the 

 beds. 



(2.) The movements of sand consistent with these observed facts. 



(3.) The necessary actions of the water to produce these movements 

 in the material of the beds. 



Observed fads. — Amongst the most general facts to be observed as to 

 the arrangement of the material forming the beds of estuaries are — 



(1.) The general stability or steadiness of these beds, so far as is shown 

 by their outline or figure, while, at the same time, as is shown by the 

 obliteration of all footprints and markings casually placed upon them, 

 also by the ripple mark, the material at the surface of these beds is being 

 continually shitted. 



(2.) The almost absolute steadiness in figure of some of these beds. 



(3.) The gradual changes in the position and form of others — the 

 growth or accumulation of sand-banks in some places, and the wasting of 

 banks or removal of sand in others. 



Movement of sand. — As regards the movement of sand consistent with 

 these change?, in the first place the movement, whatever it may be, is one 

 of the surface, and not one in bulk ; and in the next place such movement 

 of the surface must be continually going on, whether it produces any 

 change in the figure of the banks or not. The invariable obliteration of 

 footprints and marks which may have been left on the sand at low water, 

 as well as the ripple marks, are absolute evidence of a general disturbance 

 of the surface, and it requires but little observation to show that this dis- 

 turbance is of the character of a drift of sand, in whatever direction the 

 water may be moving. 



Uniform drift. — Where the outline of the banks is not altered, this 

 drift or motion of the sand must be uniform, as much sand being de- 

 posited at each point as is removed from that point. Although there may 

 be a general flow of the sand in some direction, if the drift is uniform this 

 movement will not alter the figure of the bed, which, like the balance in 

 another kind of bank, does not depend on the rate of deposit and with- 

 drawal, but on the excess of one of these over the other. The gradual 

 accumulation or diminution of sand at any point is clearly not due to a 



