436 



F A R M E RS' R E G I S T E R. 



[No. 



an iinuiediaie yiop to tlie mvuges boili of floods 

 and low waler, niighi couuleibalance thai de- 

 fect. 



But, in moa:t hilly disJtricta:, the, currents are ve- 

 ry rapn!, and, cunse(|nently, the sand-beds are so 

 liequendy renewed by the action ot the vvaier, that, 

 in many insiancef?, it is exlienicly ditficuh, and 

 dangerous lo meddle with tiiem. And miless the 

 eiie of improveuienl be of such a magnitude that 

 it will allow i-he new channel through tlie sand-bed 

 to be large and deep enough to contain the largest 

 flood without rising over its banks, it should never 

 be meddled with. The strengih required depends 

 on the weight of water, the Ibrce of tiie current, 

 and the angle of deviation from the given direc- 

 tion of the current immediately above. If the re- 

 quired direction of the barrier be nearly the same 

 as that of the current above it, as in the last dia- 

 gram, it has little more than the weight of the wa- 

 ter to withstand; whereas a jutment run out ab- 

 rupUy into the natural course of the current, as is 

 conmionly done, has not only the wei<j:ht but the 

 force of the water to sustain, and requires ten-fold 

 the strength of structure. 



The height and base of tlie barrier also require 

 particular atiention. The greatest care ought to 

 be talcen in giving it a sulficient base and height, 

 )S0 that the highest floods do not make their way 

 over the top contiguous to the hank; fiir if it be not 

 raised high enough to prevent the water of floods 

 from making its way over it, not only the founda- 

 tion may be endangered, but a large hole might be 

 scooped out behind, especially in a place where 

 the general fiill of the river is considerable; so that, 

 instead of protecting the injured part, more dam- 

 age would be done. 



The materials of a river-guide ought to be suit- 

 ed to its occasion. Where stones can be procured, 

 they make the most permanent defence; but in dis- 

 tricts where they cannot be got but at an immense 

 expense, brushwood and whins wattled together 

 with short stakes make a tolerable suostitute. In 

 most hilly districts large rough stones are plentiful. 

 A long pile of loose stones laid flatly, sloping 

 against the bank of" the river, or a flat ridge run 

 out from it, may form a cheap and durable barrier; 

 for should they be disturbed by an extraordinary 



flood, they may be readily replaced when the wa- 

 ter subsides. 



It may be proper to noticeanother casein which 

 a barrier, or river-guide, may be employed with 

 good advantage, namely, where a stream of the 

 above description falls down a crooked valley, and 

 necessarily takes, at certain points, a winding 

 course, as in flgureo. 



If the quaniity of water is considerable, its fall 

 rapid, and especially if it is. conducted to the bend, 

 as at a, down a straight unobstructed reach, scarce- 

 ly anything but substantial mason-work can resist 

 its Ibrce in that part. 



In situations of" this sort, it is not uncommon to 

 see earth banks scooped out and undei mined, un- 

 til a perpendicular precipice of twenty or thirty 

 feet high be formed. 



But if a barrier be erected at b, with an easy 

 curve fl'om the natural course above, so as to bend 

 the current without breaking it, and direct it into 

 Its natural channel in the valley below, it will have 

 nothing to contend with but the loose gravel-beds 

 c and a, which, if cut through, as in the lormer 

 case, will be gradually removed, and the principal 

 part of their materials be deposited in the bays e 

 andj^, but more especially in the latter; in this as 

 well as in that case, both sides of" the river will be 

 benefited by the alteration. 



There are cases, however, in which nothing but 

 sheathing the whole of the injured part can be 

 properly used to prevent further depredations ; as, 

 first, where the river runs through a valley whose 

 substratum is mostly gravel, as it f"requenily is in 

 mountainous districts ; and, secondly, where a deep 

 pool of water occurs in any part which may require 

 to be bent and protected to an unalterable channel. 

 In such cases, it is extremely difticnlt to get a 

 proper foundation for a barrier. In hilly situations 

 stones are generally plentiful, and they ought to be 

 applied in such a way as the given case may require. 



If the foot of the injured bank be covered with 

 a pool at low water, shelve ofi" the brink of" the 

 bank, and pour down loose stones f"rom the top of 

 it, suflering them to form their own slope in the 

 action of iidling, continuing to pour them down 

 until ihe whole spare of the injured side of the riv- 

 er form a slope of fbrly-five degrees. 



But where a built barrier cannot be avoided, as] 

 at 6 in figure 5, the foundation ought to be laid 

 pretty deep, to guard tigainst any accidental scoop- 

 ing of the Hoods. The wall ought to be carried up 

 dry, or without mortar, the stones being laid with 

 their smaller ends outwards, and their inner ends 

 pointing to the centre like those of an arch, back- 

 ed with hard materials. In forming a barrier of 

 this sort, the largest stones should be used where 

 the current strikes most forcibly against it; there, 

 likewise, the greatest elope should be given to the 

 wall. 



The coping, or uppermost course of stones, is to 

 be secured with tough sods, whose surface ought 

 to be even with that of the stone-work; and similar 

 sods require to be laid, with a gentle rising elope, 

 until they unite smoothly with the natural turf of 

 the land defended, so that the water of floods, 

 when It rises above the stone-work, may have no 

 projection to lay hold of, but may glide away 

 smoothly. 



A bulwark of this sort, like every other species 

 of river ftjnce, requires to be attended to from time 

 to time, especially after great floods, if the fbun- 



