RIVER. 



Dope brock, the upper part, to give freedom to floods of 

 higher magnitude. But that where it is in the face of an 

 impetuous torrent, and at fome little diftance from it, a gravel 

 bed is thrown up, fo as to lie dry during low water ; yet 

 where lands, behind, are liable to the ravages of floods, as is 

 often the cafe, and efpccially where ftones are not plentiful, 

 a more frugal arrangement of them may be made, by uiing 

 them merely to cafe the expofed bank, fo as to prevent the 

 currents of floods from laying eafy hold of it, and tearing 

 away the land. However, in this cafe much depends on 

 the plan and conitruction of a fafeguard of this kind. It 

 ought to be every way convex ; fo that the itrength 

 of the current and the weight of the water may act upon 

 it, as fuperincumhent preflure acts upon an arch. It fhould 

 bulge out, horizontally, towards the known current of 

 floods, (without regard to the courfe of the ftream at 

 low water,) and the face of the wall ought to take the bar- 

 rel form. A crofs fection of the ftone-work fhould refemble 

 a femi-arch, or, in dangerous fituations, it ought, it is con- 

 ceived, to fall back flatter than the quadrant pitch. For, 

 in general, the flatter it is made to lie, the more fecure it 

 will become ; but the fteeper it is carried up, the fewer ma- 

 terials, and the lefs labour, it will require. And in forming 

 a work of this nature, the foundation fhould be laid pretty 

 deep, to guard againft any accidental fcoopings of the 

 floods. The wall ought to be carried up dry, or without 

 mortar, the ftones being laid with their ends outwards, their 

 inner ends pointing to the fame centre, like thofe of an arch, 

 and to be backed with gravel or earth, rammed in firmly 

 behind as the facing is carried up. The coping, or upper- 

 molt courfe of the ftones, fhould be fecurely bound with 

 thick tough fods (eight or ten inches deep), whofe furfaces, 

 when beaten down, ought to lie even with that of the ftone- 

 work ; and fimilar fods require to be laid, with a gentle 

 rifing flope, until they unite fmoothly with the natural turf 

 of the land to be defended : fo that the waters of floods, 

 when they rife above the ftone-work, may have no abruptnefs 

 to lay hold of, but may pafs away fmoothly over the fur- 

 face of the land, as they commonly do over fmooth green- 

 fward, without injury. And, laftly, that the ftones are to 

 be beaten forcibly into the bank with a rammer, a mallet, 

 or a fmall battering-ram adapted to the purpofe ; thus ren- 

 dering the whole compact and firm to relift the current. 

 Where vacancies or fiflures it ill appear, long fplinters of 

 ftone are to be driven in, as wedges, to increafe the firm- 

 nefs, and prevent the current from tearing out an unguarded 

 ftone. It follows, in courfe, that the largeft and longeft of 

 the ftones ought to be ufed where the greateit rcfiltance is 

 known to be neccflary, in order that the greater fecurity 

 may be attained. It is remarked that this fort of defence, 

 like that of every other fpecics of the river kind, requires 

 to be attended to from time to time, efpecially after great 

 floods. If the foundation be laid bare, it requires to be re- 

 covered with rough gravel, or with ftones thrown loofely 

 againft it. If any of the facing ftones be difplaced, or 

 loofened, they are to be replaced with others, or to be 

 wedged in afrefh. Or if the turf which binds them at the 

 top be dilturbed, the torn part fhould be cut out fquare, and 

 be firmly and completely filled up with frefh turves. It ia 

 jdded, that this method of defence againft rapid rivers ori- 

 ginated in the ingenious writer's own experience and prac- 

 tice ; and that, when compared with a wooden guard, it is 

 cheap, fightly, and durable. 



It is .noticed further, that there are cafes of other kinds, 

 js thofe which are found in the fkirts or margins in the val- 

 lies of mountainous fituations, through the plains of which 

 tire rivers are found winding with devious courfcs, or tracing 



Vol. XXX. 



the margins at the feet of the containing heights. In fome 

 inftances, they are confined in deep-funk channels, whofe 

 banks they feldom overflow ; but, much oftener, their chan- 

 nels are funk a few feet only beneath the general furfaces 

 of the lands they pafs through. Hence, in high floods, 

 they may be laid to be let loofe over the plains, to ravage 

 them at pleafuic. Their immediate banks, however, are 

 generally the victims of their rage. Thefe they tear away, 

 and ranfack off their better parts ; fubftituting beds of 

 ftones and gravel, or perhaps their own channels, in the 

 ftead of what were, a few hours before, valuable lands. 

 And that there are inftances of mountain torrents, on rufh- 

 ingout of their confined channels into flat vale diftricts, ra- 

 vaging many acres during a fingle flood. And to confine or 

 direct thefe, in, it is obferved, often a bufinefsof vait diffi- 

 culty and trouble. 



In thefe cafes, the belt endeavour of the artift is gene- 

 rally, according to Mr. Marfhall, to give the river a direft 

 or ftraight-forward courfe, on its quitting its reftraining 

 channel, at its firft entrance into the area of the plain ; and, 

 if no obltruttion lies in the way, to continue the ftraight 

 line to another retaining channel, at the lower end of the 

 area to be improved. But that where the area is winding, or 

 fome obflruction rifes within it, fo that a ftraight line can- 

 not be drawn from the entrance to the outfall, an infuperable 

 difficulty may feem to fruftrate this mode of improvement ; 

 as the current requires to be bent, not only after it has en- 

 tered the plain, but after it has acquired an increafe of velo- 

 city by moving in a ftraight courfe. By actual practice and 

 experience, he was led by another circumftance belonging to 

 it, to what may, perhaps, be confidered as a principle, in 

 conducting improvements of this nature. A ftraight cut 

 into the middle was defirable : but the point of rifing- 

 ground rendered it impracticable. Near the centre of the 

 flat, a large infulated fragment or iflet of rock rofe ten or 

 more feet above the level of the area ; and at the lower end 

 of it, near the natural outlet of the river, a bank of rock 

 had formerly been wafhed by it. It was eafy to perceive 

 that the infulated rock, whicli commanded both the extreme 

 points of the area, might be employed in uniting them ; and 

 that, by the ufe of that rock the work might be rendered 

 complete. For, by opening a ftraight courfe to the rock in 

 the middle, and another from thence to the bank of rock at 

 the outlet, the current would be directed, in another ftraight 

 line, to the outlet, and the fcite of improvement be entirely 

 freed from its injurious effects. He remarks, that it is in 

 few inftances that prominent rocks, firm enough to refiit the 

 current of an impetuous river, rife in the areas of river- 

 worn plains. But that, on the fides of mountain vallies, 

 rocks are common ; and may, doubtlefs, in many inftances, 

 be employed to throw the river from fide to fide of a crooked 

 valley, in ftraight reaches ; as rays of light may be reflected 

 in continuation by well-placed mirrors. Even where natural 

 rock is uot prefent, either in the area, or on the fides of 

 fuch a plain, or thit-bafed valley, rifing grounds may fre- 

 quently be found within the former, and are never wanting 

 on the fides of the latter. And, againft thefe, artificial 

 hutments, of fufficient ftrength, may not untrequently be 

 formed in alpine- fituations, where (lone-- are generally plen- 

 tiful, without any very great expencc. 



It is obferved, in refpect to the altering the courfe of a river 

 or brook, that the difficulties and expence depend on the,par- 

 ticular circumflances belonging to it. In a limple cafe, in 

 which one ftraight cut only ia required, the principal diffi- 

 culty, and that which requires the belt fkill of the artill, 

 lies in directing the current of the tirlt flood out of the old 

 into the new channel. But if a bend of the old channel, 



T t hkr 



