WEIR. 



ftream and other circumftariMS may be. The height of it is 

 always equal to the depth of the ftream compared with the 

 adjacent land. 



The water of a very fmall and gentle ftream may often be 

 diverted for this ufe, by means of a few fods firmly put 

 down, with fome Hones above them : but for lands of any 

 confiderable extent, the kinds direfted below are necefTary, 

 according as the ftrength of the refpedive ftreams may hap- 

 pen to be. 



Strong wooden beams or balks thrown acrofs the Itream, 

 and made clofe by means of boards well fecured, are, m 

 many cafes, fufficiently ftrong, commodious, and conve- 

 nient, in (low moving waters, of no great power or 

 force. 



A few cart-loads of ftones thrown properly in acrofs the 

 ftream, forms alfo a bulwark, wide at thebafe, and narrow- 

 ing towards the top, the whole being puddled with clay or 

 oravelly earth, which fometimes anfwers well. Over the 

 top of this bulwark, the fuperfluous waters pafs in a free 

 manner, falling down the gentle flope, to which, if well con- 

 ftrufted, they do no fort of injury. 



A weir fuitable for a fmall river may confift too of feveral 

 rows of ftakes, firmly driven down and interlaced with the 

 branches of fir-trees, the intervals of the rows being filled 

 with Hones. The fand and mud that come down with the 

 floods fill up this fort of weir, and render it fit for effefting 

 its purpofe. In heavy rains the fuperfluous water pafles en- 

 tirely over. 



But for more powerful rivers, the weirs may be con- 

 ftru Aed of ftrong frame-works of wood, firmly and ftrongly 

 joined together, and the different compartments all paved 

 with large ftones : the weir rifing very gradually againft the 

 ftream, and being made to flope gradually away before it, 

 as it flows over it. In this way the largeli and moft power- 

 ful rivers may moftly be managed, if the weirs be well 

 fuited to them ; fo that it is but in few cafes advifeable to 

 attempt the watering lands from rivers that cannot he di- 

 verted by one or other of thefe forts of weirs, as the ex- 

 pence and hazard taken together may greatly exceed the ad- 

 vantage to be derived. It may, however, in fome cafes of 

 large rivers, be neceflary and proper to have recourfe to 

 more expenfive weirs, fuch as that defcribed below. 



In this weir, which was formed on a large, rapid, and 

 ftrong river, under the direftion of the Rev. W. H. Co- 

 ham, in Devonfhire, after the ftream had been temporarily 

 diverted, and every thing removed for a proper foundation, 

 a double row of pits was dug into a rocky fubftratum, di- 

 reftly acrofs the bottom, or bed of the river, at about five 

 feet afunder lengthways, by four feet in breadth, and about 

 two feet in depth ; and into thefe pits oak pofts of about 

 fix or feven inches fquare were fixed. The mafon then raifed 

 a perpendicular wall, without any cement, about five feet 

 and a half thick, entirely enclofing the pofts, the labourers 

 being employed in the mean time in backing up the wall on the 

 higher fide with fome of the Jliffejl clay to be had. This 

 was, however, afterwards found to be wrong ; it ftiould 

 have been done in the puddle manner, by means of mould and 

 gravelly earth. 



When the wall was raifed to fuch a height as was deemed 

 neceffary, in relation to the level required, and the preferva- 

 tion of the lands adjacent, the upper parts of the oak pofts 

 were fawn off, in order to receive crofs-pieces and joifts, the 

 front pofts being then left to ftand about fix inches higher 

 than the hinder ones ; and on thefe joifts oak planks were 

 pinned, about fix feet and a half long by three itiches 

 thick. Thefe planks were brought forward to projeft about 



one foot and a half over the perpendicular of the wall, on the 

 lower fide, forming a fort of lip, as it has been termed ; the 

 clay, together with thefe planks, conftituting an inclined 

 plane, and terminating at the diftance of about fifteen feet 

 up the ftream, on the common bed of the river. 



The entrance for the leat was cut at about thirty feet 

 above the Up of the weir, where, to regulate the quantity 

 of water to be admitted, three ftrong flood-hatches, to be 

 lifted or let down by a lever and windlafs, were placed ; 

 and through which a column of water, of about eight feet 

 in width by four feet in depth, may be introduced at any 

 time. Between the leat and the river a ftoue wall, ftrongly 

 cemented, is erefted, which is about eight feet in height, 

 and carried from the head of the leat to about thirty feet 

 below the weir, in a parallel line with the river, and at the 

 end of which wall another flood-hatch is fixed on a level with 

 the bed of the river. This latter hatch will always be of 

 great advantage when any reparations may be wanting on the 

 weir ; as on drawing it up when the water is low, the weir 

 in a few hours will be left perfeftly dry, and the workmen, 

 with the greateft convenience, may proceed in their opera- 

 tions. From the top of the fide wall, above the weir, the 

 ground is made floping to the river, and below it is covered 

 with turf, and levelled as a foot-path. 



Immediately below the weir, m this cafe, there is an out- 

 let regulated by another flood-hatch, and condufted through 

 3.JlDoot formed of oak plank, from the leat, and contrived for 

 the admiffion of falmon, which are there fometimes taken ; 

 and below the lower flood-hatch, a trap, or luilley, as it is 

 there termed, is made for the catching of fmaller fifh : this 

 part of the work does not, however, properly belong to this 

 kind of weir, therefore it need not be more noticed. 



The height of the weir is about four feet above the level 

 of the river where it is fixed ; and its length, from bank to 

 bank, direftly acrofs, or at right angles with the ftream, is 

 about forty-eight feet ; forty feet of which is carried at a 

 perfedl level, and over which the water falls precifely at the 

 fame depth, forming a beautiful cafcade. The remaining 

 portions of the length of che weir, namely, four feet on 

 each fide, are raifed, gradually afcending to the banks for 

 the purpofe of warding off the torrent from them in time of 

 floods, when the river, in this cafe, is very tunuiltuous. 



The lip part of the weir is found to anfwer perfedlly ; as 

 in proportion to the force of the water behind, fo is the dif- 

 tance which it is thrown over the weir from the foundation of 

 the perpendicular wall. 



If the writer had not been foiled, and had part of the 

 work to perform over again, in confequence of the ufe of 

 clay, as already noticed, being under the neceflity of driving 

 on the weir in a direft line with the former work, into the 

 fide of the oppofite bank, as before ; and after removing as 

 much of the clay as could be got at, which will not unite 

 completely with the foil, but become liable to be under- 

 mined by the water, by making a puddle, as ufed in canals of 

 mould and gravel, in its ftead, which fucceeded in a com- 

 plete manner ; the whole coft of the weir would not have 

 exceeded 75/. 



This weir or wear, from its prefent appearances, may 

 now, it is faid, feem to bid defiance to time ; and be fafely 

 recommended as a pattern to thofe who may have occafion to 

 conftruft any thing of a fimilar kind, either for watering 

 land, for machinery, or other ufes. See Watering 

 Land. 



In the weirs or wears which are thrown over large rivers 



for the purpofe of raifing the water for the ufe of mills, and 



in many other intentions, and which are moftly conftrufted 



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