1839.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



107 



befoie-nientioned at abovit every ten yards, and a regular register and 

 jonrnal is kept of the whole proceeding-, so tliat the actual slate of 

 the work at any one period can be ascertained with accuracy. 



The work h is now been in operation nearly twenty-six years, but 

 the great bulk or mass of the work, whicli renders the Sound a well 

 protected roadstead, was completed ten or twelve years ago. The 

 o|)erations are now cluetl}' confined to tlie west end, where they are 

 employed upon making' the solid masonry foundation for tlie light- 

 house, wliich is a work requiring a good deal of nicety and time to 

 complete, particularly the foundation courses, which are to be laid by 

 tlie diving-bell ; but on account of tiie swell which so frequently pre- 

 vails there, many days elapse when it cannot be useil, so that the 

 Breakwater, with the exception of this ])art, may be said to be almost 

 completed. The original estimate of tlie late Mr. Rennie for the rub- 

 ble alone, witliout the masonry, casing, or lighthouse, was, I think, 

 1,150,000/., and these two latter works have been estimated at from 

 250 to 300,000/. more, so that the whole will not exceed l,.'i0O,O00i'. ; 

 which I trust will be allowed as coming very near to the original cal- 

 culations, considering the difficulty of works of this nature, exposed as 

 they necessarily are to the vicissitudes of the elements, which render 

 them peculiarly liable to casualties. 



For the above short account, I trust that I have fully com])lied 

 with your wishes as far as the short period of notice you have given 

 would allow. I believe that I have not omitted any very material 

 point, although you are fully aware that there is a great deal of detail 

 which could not be included in such a necessarily confined account — 

 it is of less importance now, as it will be included in my work 

 previously referred to. The accompanying drawings, from which the 

 work has been executed with some slight modifications according to 

 circumstances combined with the above descriptions, will, I think, 

 render the whole subject sufficiently intelligible. 



Uelieve me very sincerely, 



Luiiilon, April 6, 1839. John Rennie. 



A TREATISE ON RESERVOIR LOCKS. 



ISV ,1. A. ROEBLrNO, CIVIL ENGINEER. 



(From the American Railroad Jonrnal.) 



By the term reservoir locks, is understood locks connected with 

 reservoirs which receive and reserve a certain portion of the lockage 

 water for the purpose of floating a vessel fiom one level to another, 

 and which reserved portion of water is let into the lock-chamber again 

 when another boat is passing the lock. As the reservoirs are alter- 

 nately drawing and discharging a certain portion of the water, it is 

 obvious that tliey may be so located as to use a far less (piantity of 

 water for passing vessels through the lock than is commonly wanted. 



These preceding remarks will be sufficient to attract the attention of 

 engineer's, and lead to the suggestion that this kind of lock is of the 

 greatest importance in a country where the summer season is generally 

 dry, and where the want of a sufficient supply of water for lockage often 

 interfcr-es with navigation ; furtliei-, that by means of these locks expense 

 will he saved, and that a canal may be constructed, and kept navigable, 

 where iir the other ca;e sufficient water could not be furnished for sup- 

 plying common locks of ordinary lifts. An eminent engineer in Eng- 

 land, where this subject is at present treated with much irrtcrest, lately 

 ckiimed to be the inventor of these locks, but without any right. As 

 far as the writer of this is informed, but one lock of the kind in ques- 

 tion has ever been constructed itirtil this day. This lock was built iir 

 France, under the reign of King Louis XIV., by an eminent engineer 

 at that time. M. Bclidor, in his " Architectura Hydraulica," gives a 

 brief account, and a crosssection of that lock, which has abontlwenty 

 feet lift, and stands at the point of junction of two canals. The level 

 of one canal lies twerrty feet above the level of tlie other, and the 

 lower canal is supplied with the necessary water by the upper one. 

 The grouird at the jiiiirtion, in the dircctioir of the lower canal, di'ops 

 down at once, and ottered a favourable opportunity for the construc- 

 tion of a high lift-lock, with reservoirs. Tlie head of that lock is con- 

 structed in two ofl>els, with two upper gates to divide the pressure of 

 the water against the gates. Tliis lock answers the purpose in every 

 respect, arrd draws irot quite seven feet water frour the irpper level, for 

 passing a boat throrr^h the clranrber. About three minutes of time 

 moi'e are required, when the two reservoirs are used, than when not, 

 far the passing of a boat, and there is rro more stamping of the boats 

 during the passage than in a lock of seven feet lift, as the head of the 

 water-pressure is never above seven feet. 



The first locks of this kind, in this country, are now being con- 

 structed on the Sandy and Beaver Canal, under the directiorr of Mr-. 

 E. H. Gill, Chief Engineer on that line, who bv this improvement will 

 considerably add to the already well establislied credit which that work 

 greatly deserves, for the superior construction of its spleirdid locks and 



No. 19 — Vol. II — ksmt, 1839. 



dams, and, in fact, for lire solidity of all the works. Mr-. E. H. (iiU 

 occasioned the writer to examine into the natirr-e of this object to es 

 tablisir its theory, and demonstrate formula" for compirting the best 

 dimensions of the r-eservoirs, the location of the commurricating culverts 

 and valves, arrd the water saved. He afterwards experimented with a 

 model, to see how the theory agreeil with the reality, arrd satisfied 

 hinrself in every respect as to the practicability and the utility of 

 r'cservoir's. 



As the saving of water depends on the number of leservoir-s attached 

 to a lock, their ai'eal extension, and on the placing of the culverts and 

 valves, this matter nrtrst be rightly understood, arrd all dimerrsions 

 nrnst be fairly calculated, which cah'ulations, however', are vei-y easily 

 performed. I otIi?r here a general demoirstratioir of the theory of this 

 object, which for its plainness will easily be understood. 



The nrrmher of reservoirs attached to one lock, may be one, two, 

 three, four, and cveir inor-e ; a gr-eater number than four seldom will be 

 required, and found applicable : in nrost cases two reservoir-s will an- 

 swer tire purpose. But there may be locations fourrd where the grourrd 

 off. 'IS sufficient i-oom, and sirits well for the construction of four reser- 

 voirs, two on each side of the lock, and where by these means a ver-y 

 great saving of water will be obtained. 



The annexed drawing, fig. 4, shows tire cross-section of a lock of 

 fourteen feet lift, with a reservoir of 5,400 superficial square feet, on 

 each side. The diagrams 1 , 2, and 3, are likewise to represent cross - 

 sections of the lock-chamber and reservoirs on each side. By the linear 

 shadings are represented the different stages which the water will alter- 

 nately occupy in the chamber, and in the reservoirs. Tlie lirres A B 

 and S M r-epresent the irpper level, and the lower level, in all the dia- 

 grams ; and by the lift of the lock, is to be understood the elevation of 

 iire upper level A li above tlie lower level S I\I. These two levels 

 are supposed to be always permanent, and not to be altered. 



Fig. 1. 



To make the case mor-e simple, it is supposed that each reservoir is 

 to be as long as the lock-chamber is in the clear, and twice as wide, 

 so that the ar-ea of each reservoir be equal to twice the area of the 

 chamber. Let the required height which the water will occupy in the 

 upper reservoir, be denoted by the letter x ; the height of water in tha 

 lower reservoir-, be denoted by y. 



By examining the fiist diagr-arn, any one will admit the following 

 srrppositions : — 



1. Ulien the valve of the upper reservoir is opened a quantity of 

 water A BC 1' of the chamber will enter the reservoir and will flow in 

 till the water surface in the chamber and reservoir, C P and P I), form 

 one level. Now, suppose this reservoir shut, and the valve of the 

 lower reservoir opened, the quantity of water marked by tJPQH will 

 escape and enter the lower reserv..ir, till the water surface is sunk to 

 an equal level (i (J H. After the lower reservoir is shut, ther.' remains 

 a quantify of water in the chamber, marked by the letter's 1,JI1SM, 

 which lies above the lower level, and of coui'se must be drawn oft' into 

 the lower canal, in order to clear out the boat. 



2. Now, take the case reversed : when a boat is to pass from the 

 lower level to the upper level. After the boat has entered the chamber 

 and the lower gates arc shut, open the paddle of the lower-reservoir, 

 and di-aw the reserved water into the chamber-. All dimensions being 

 right, this quantity of water should exactly till out the space S iNI O K, 

 so that the top water line, O K, and the bottom of the reservoir, I O, 

 be in one level, and no water remains in tlie reservoir above that level. 

 The boat will now be raised to the level of O K. After the lower 

 reservoir has discharged itself, shut it, and open the paddle of the upper 

 reseivoir-, and dr-aw oH'its r-eserved content of water. This qirantity of 

 water should exactly occupy that space in the lock chamber marked ln-_ 

 E N O K, so that no water remains in the reservoir above the level ot 

 N F, repr-esenting the bottom of the upper reservoir. To raise the 

 boat to the level of the upper canal, a quantity of water A B F. N is yet 

 reqrrired, which mirst be drawn from the upper level into the chamber, 

 after the valve of the upper reservoir is shut up. 



In the first case, that quantity of water whidr has actually been 

 drawn from the upper level, is maikwl by the litres S M O K, the 

 quatititv of water saved is marked by A B Q H. 



