THE LAW THAT GOVEKNS THE ACTIOI?- OF FLOWING STREAMS. 733 



38. On the Law that governs the Action of Flowing Streams. By 

 K. D. Oldham, Esq., A.E.S.M., F.G.S., Deputy Superintendent, 

 Geological Survey of India. (Read January 11, 1888.) 



Of all the agents which Nature employs in her great and ceaseless 

 work of change, of destruction and construction, of removal and 

 renewal, probably none have been less studied, few are less under- 

 stood, by geologists, than water in the form of streams and rivers. 



In a general way it is known that, with sufficient velocity, a stream 

 will erode its bed, and that if the velocity be reduced sufficiently it 

 will deposit part or all of what solid material it may be carrying 

 down its course. But, while mathematicians and engineers have 

 been investigating, in all their details, the laws which govern the 

 flow of water, geologists have done little to investigate the laws 

 under which it acts in shaping the surface of the world we li\'e in. 



Eain, glaciers, and the sea ; these seem almost to have limited the 

 horizon of the geological view, and, without forgetting the researches 

 of Prof. Hull, the essay of the late Mr. Greenwood, or the application 

 of the principles enunciated by him to a special case by the late Mr. 

 Eergusson, we may almost say that the intermediate link in the 

 chain — the flowing stream — has either been regarded as unworthy 

 of notice, or the vague general ideas and statements of the textbooks 

 have been regarded as a complete and satisfactory account of the 

 problem. 



Yet in the whole range of physical geology there is no subject 

 which will better repay a detailed investigation or open a wider 

 field of intricate and interesting problems than this : and it is with 

 the hope of being able to contribute something to our knowledge of 

 this almost unexplored region that this paper is laid before you. 



My attention was first drawn to this subject when at Hardwar in 

 December 1883. In course of the operations for constructing new 

 head-works to the Ganges Canal a small driblet of water began 

 to eat into sand, over which it had flowed previous to the removal 

 of a block of masonry. I noticed that only in certain parts of its 

 course did it erode its channel and that there were intermediate 

 reaches where there was no erosion, or, when it had assumed a 

 nearly permanent condition, even deposition. The areas of no 

 erosion, or deposition, gradually encroached upon the channels of 

 erosion above them and were themselves encroached upon by the 

 channels of erosion below. 



Acting on the hints obtained, I commenced an inductive investi- 

 gation into what should be the action of a stream flowing over a 

 uniform deposit, whether of its own formation or not. This, with my 

 subsequent inquiries into the truth of the deductions arrived at, will 

 be presented in the following pages. 



The fundamental principle on which all such investigations must 

 be based is one of great simplicity, though its application leads to 



Q.J.G.S. No. 176. 3 c 



