1849.] On the Embankments of Rivers. 701 



wider or narrower stream with a momentum due to gravity, ever im- 

 pelled in the direction of the lowest level, and passing through a re- 

 sisting medium of earth, or sand or gravel. The river is first deflected 

 to one side by an obstacle on its right, and then impelled back again 

 by an obstacle on its left, but as it has also an onward motion of its 

 own, the result of these mutually influencing forces is a series of oscil- 

 lations on either side of a central line. This is illustrated by a top 

 spinning at an angle, or by a carriage swaying to and fro on an uneven 

 road, which will not always upset, although its centre of gravity may be 

 off the perpendicular. The bounding of a ball along a plain, or the 

 surface of a lake, is also to the point. It is urged upward by the resist- 

 ance of the water, it inclines downward from gravity, and it is impelled 

 forward by its original momentum, — the result being a waving line of 

 progress in a vertical plane, similar to what a river exhibits on a hori- 

 zontal plane. I do not think these deflections and windings of rivers 

 have ever been investigated analytically and reduced to formulae, but 

 their determination is of practical value, and I hope that a competent 

 mathematician, like Mr. Pratt, may be inclined to give his attention to 

 the subject. 



The proper system of embanking obviously that proposed. — These 

 characteristics of rivers being admitted as true, it is plain that the 

 country generally should be protected by embankments formed on the 

 verge of the belt of variation, and that lands within the belt should be 

 protected by inferior embankments, over which an unusual flood may 

 sweep, and so perhaps destroy them, but without reaching the summit 

 of the main lines. It is not proposed to enter into the details of the 

 construction of these dikes, which must vary according to soil, exposure, 

 &c, but it is obvious that the smaller ones should always allow a 

 moderate space, called a " free-way," on either side of the channel for 

 the time being, that neither set of embankments should form sharp 

 angles, but rather bend the current by means of a rounded trace, and 

 that for the same reason the inner sides of the " bunds" should slope 

 gradually into the country or towards the river, although the outer 

 faces may be as perpendicular as the nature of the soil will allow, or as 

 circumstances may render convenient. 



Embankments modify the tendency of rivers to raise their beds, and 

 complicate the conditions rendering remote, but total changes of course 



