Book III. 



GUARDING RIVER BANKS. 



19 



Sect. II. 



Guarding the Banks and othenvise 

 Streams. 



improving the Courses of Rivers and 



4358. The subject of guarding the banks of rivers is of considerable interest to the 

 proprietors of lands situated in hilly districts, where, in the valleys and on the hill sides, 

 the streams often produce ravages on the banks, and sometimes change their courses. 



4359. The natural licence of rivers, Marshal observes, is not only destructive of 

 landed property, frequently of lands of the first quality ; but is often the cause of dis-. 

 putes, and not unfrequently of legal contentions, between neighbouring proprietors. A 

 river is the most unfortunate boundary line of an estate. Even as a fence, unless where 

 the water is unfordable, a river, or rapid brook, which is liable to high floods, is the 

 most tormenting and inefficient. Proprietors have therefore a double interest in ac- 

 commodating each other, as circumstances may require, with the lands of river banks, 

 so as to be able to fix permanent boundary lines between theii properties. When the 

 owners of estates cannot, by reason of entails or settlements, or will not for less cogent 

 reasons accommodate each other, they have a line to tread which they cannot deviate 

 from with prudence, much less with rectitude ; namely, that of cautiously guarding 

 their own lands, without injuring those of their neighbours ; for a lawsuit may cost 

 ten times the value of the sand banks and islets of gravel to be gjiincd by dexterity of 

 management. 



4360. The operations for improving rivers have for their object that of preventing 

 them froin injuring their banks, of accelerating their motion, and of lessening the space 

 of ground which they occupy, or altering their site. These purposes are efitected by piers 

 or guerdes for altering the direction of the current ; works for protecting the banks j and 

 by changing or deepening the river's course. 



4361. The 2>rinciples on which these operations are founded are chiefly two ; first, that 

 water, like every other body when it impinges on any surface, is reflected from it at a 

 similar angle to that at which it approached it ; and, secondly, that the current of water, 

 other circumstances alike, is as the slope of the surface on which it runs. On the first 

 of these principles is founded the application of piers for reflecting currents j and on 

 the second, that of straightening rivers, by which more slope is obtained in a given 

 length of stream, and of course greater rapidity of motion obtained. 



SuBSECT. 1. Guarding River Banks. 



4362. A common cause of injury to the banks of rivers is produced during floods. A 

 tree or branch carried down by a stream, and deposited, or accidentally fixed or retained, 

 in its banks, will repel that part of the stream which strikes against it, and the impulse 

 (counteracted more or less by the general currentj will direct a substream against the 

 opposite bank. The effect of this continual action against one point of the opposite 

 bank is, to wear out a hole or breach ; and immediately above this breach it is customary 

 to place a protecting pier to receive the impulse of the substream, and reverberate it to 

 the middle of the general stream. But if this pier is not placed very obliquely to the 

 substream, as well as to the general stream, it will prove injurious to the opposite bank 

 by dii ecting a subcurrent there as great as the first ; and, indeed, it is next to impossible 

 to avoid this ; so much so, that Smeaton, in almost every instance in which he was con- 

 sulted in cases of this sort, recommended removing the obstacle where that could be done, 

 and then throwing loose stones into the breach. 



4363. Injwies by floods, according to Marshal, are to be remedied in two ways ; 

 the one is to sheath the injured banks of the bays {fig, 671. a, b, c) with such materials 



^^'^mmmmmm 



as will resist the circuitous current ; and let the river remain in its crooked state. The 

 other, to erect piers (rf), to parry off the force of the current from the bank, and direct it 

 forward ; with the twofold intention of preventing further mischief, and of bringing back 

 the course of the river to its former state of straightness. It is to be observed, that the 

 operation of guarding the immediate bankof asharp river bend, against a heavy current 

 meeting with great resistance, by sheatliing it with stones, is generally a work of much 



