700 On the Embankments of Rivers . [July* 



formed of an alluvium deposited by themselves and their affluents, which 

 has but little coherence. The resistance offered by the soil is no longer 

 nearly equal to the impetus of the main current, and hence all symme- 

 try of channel is lost, and the rivers resume some of the characteristics 

 of their upper courses, wandering over sand banks from one low shore 

 to the other, or during floods covering the whole country with a slow 

 moving inundation. Still the mutual action, and reaction of the stream 

 and banks tends to establish a variation within limits, and the breadth 

 of the belt of change can always be ascertained, and will usually be 

 found to exceed its measure in the central plains. But disregard must 

 be had to such alterations as that which may take the Ganges into the 

 Nattore Jheels between Bauleah, and Dacca,* and which would corre- 

 spond in cause and character with those changes of the Bansli and More 

 above described. Again, after rivers begin to form deltas, the principal 

 streams mostly continue to move onwards in their irregular courses, 

 but the smaller outlets having necessarily a diminished current, may 

 perhaps meet with so much resistance as to cause them to wind, as is 

 the case with the Bhagiruttee, Jellinghee, and other effluents of the 

 Ganges, f 



Some rivers do not exhibit all of the characteristics above described. 

 The Ganges is a good type, but the Indus and Sutlej nowhere become 

 regularly winding, as neither does the Damooda, the proper embank- 

 ment of which is an object of so much concern. The Jumna again 

 merges in the Ganges after passing through two, and the Soane after 

 apparently passing through one only, of the distinguishing conditions. 



The limits of the variation of rivers dependent on dynamical princi- 

 ples.— The limits of the deflections or windings of rivers can be deter- 

 mined on dynamical principles. The elements of calculation are, a 



* Rennell's Memoir of a Map of Hindostan. Appendix, p. 345. 



f Branchings off must always take place at an angle to the direction of the stream, 

 although sometimes they may almost form a continuation of the adjoining, or pro- 

 ducing each of the parent river. Hence the water enters the branch with a reduced 

 initial velocity, or occasionally with little more than with what is due to its height 

 as a column of fluid, and being unable to carry forward the whole of the detritus 

 with which it is charged, the coarser portions are deposited and the head of the 

 effluent becomes raised above the bed of the principal stream. Thus the head of 

 the Bhagiruttee is always, as we say, " choked with sand." 



