TRANSACTIONS OF SECTION G. 691 



•of shoals and the erection of piers, and the working of Acts of Parliament, must all 

 come within the scope of the undivided control which he advocated. 



He considered such an undertaking the more worthy of Government attention, 

 "because the requisite knowledge and experience would rarely be found in one man 

 or one hody of men, and was possessed by few even in the profession of civil 

 engineers, who would necessarily have to occupy the most prominent positions 

 and take the heaviest responsibility. 



4. On Movable and Fixed Weirs, with reference to the Improvement of the 

 Navigation, Mill Poiver, and Drainage of Flood Waters of Rivers, 

 with especial Notice of the River Shannon* By J. Neville, C.E., 

 M.R.I.A., Dundalk. 



Most rivers in their natural state, even within tidal influence, are but a, succession 

 •of pools and shallows of different lengths, the conditions of each, or its regimen, 

 depending on the varying inclinations of the hed, its natural formation, the maxi- 

 mum, minimum, and average flow from the catchment-basin and tributaries at 

 different seasons, the scouring of the bed and banks, and the formation of shoals 

 or deposits. The steepest or shallowest portions, at rapids, are but the accelerated 

 flow over natural submerged weirs of rock or coarse gravel cemented with clay 

 and sand, and the pools between, long or short, or extending into lakes (those 

 natural regulators of flood waters), constitute the deeper stretches of the river. 

 Where the river alone has to be improved for a limited navigation, a sufficient 

 depth at the shallows is sometimes obtained by running out spur weirs, thereby 

 narrowing and deepening the water-way ; or, by making a part of a continuous 

 weir movable or removable, damming up the water at times of least flow, and 

 passing down the craft employed, on flushes through the open movable portions of 

 the weir which is again raised to retain the head. As, however, the application of 

 this .system of flush navigation is limited and only available for craft of suitable 

 build, for down-stream traffic, the necessity arises for constructing locks with some- 

 times lateral navigable passes, or canals, along the shallows to connect the deeper 

 portions of the navigable river channel above and below/ The gates of such locks, 

 with their sluices for working, are only movable weirs maintaining a fixed depth 

 above at seasons when the fl<5w is limited. In some states of the regimen I have 

 occasionally seen lock-gates left open for a free navigation, the head being entirely 

 maintained by the natural obstruction of adjacent submerged weirs at the shallows, 

 and by hack water from below. 



The author, after classing the sluices and gates of movable weirs into those 

 which lift in a plane, those which turn on a vertical axis, those which turn on a 

 horizontal axis, and those that act on the principle of the American bear-trap 

 sluice, used in 1818 on the Lehigh descending navigation, and having given diffe- 

 rent examples from French and Indian rivers, concluded with reference to fixed 

 long weirs as follows : — Mill weirs are generally fixed and solid. When the 

 water supply is limited and in dry seasons, a larger quantity can he stored by ex- 

 tending the weir basin or pond and lengthening the weir, at the same time the 

 head for a variable supply is better regulated for a water-engine. To pass the 

 same quantity of water over the crest, the head there can be reduced to one-half 

 by trebling the length, and reduced in the ratio of two to three by doubling it. 

 These advantages with reference to mills must have led to the misapplication of 

 long solid weirs without even a sluice on the drainage and navigation works of the 

 Shannon. Long solid weirs sloping or curved two or three times the width can 

 have no practical advantage over those of the ordinary mean width from bank to 

 bank, on long upper stretches of a river, without proportionately extending the 

 width and depth the whole way. On the Shannon the upper obstructions in the 

 bed between weir and weir were only partially removed, and the works remain in 

 every way a sad monument for the riparian proprietors of an engineering failure. 



* The paper has been printed in extenso in ' Engineering,' for Friday, August 

 23, 1878. 



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