RESERVOIRS. 



til liar hit oon- 

 rescuer for nuch 

 nder. Hut tin- 

 such judgment. 

 misdemeanor. 

 ' : . :':'. . 



s was rescued, the sheriff 

 t> freed him from further 

 .. hmeiit for a con- 

 Uiutitl". 



.il.-n upon a final process, 

 i a rescue, and either he or 

 e rescue is effected by the 

 he pl.mitil)'. This liability 

 .re themselves, the plain till' 



rescued cannot be assumed to hare been eon 

 vicUoa and judgment, it i* not proper to a 

 oflcooec until after judgment of 

 rescuer may be indicted for a niiademamn 

 For a rescue from lawful custody is in 

 Several statutes bare, however, varied the ol 

 the punishment 



IVerioualy to the abolition of arrest on n 

 in custody of the sheriff on meene proeei 

 might make a return to that efiY 

 responsibility ; the reamers being liable to 

 tempt, and also to an action at suit of the p 



Where a party is arrested, or goods are < 

 the sheriff cannot return that there has beei 

 the jailer is in all cases, except where th 

 king's enemies, answerable in an action by t 

 is concurrent with the liability of the rescue 

 baring the option to sue either the rescuers 



(Com., Dig., 'Kescoua;' Hale, P. C. ; Hawk.. /'. ('. . Russell, On 

 Crime* ; Matthews, On Criminal Lav.) 



RESERVOIRS. In engineering works the word raercoir is tinder- 

 stood generally to apply to the Urge collections of water which are 

 made for the purpose of feeding canals, or of supplying the head waters 

 of a mill, or of supplying the water required for municipal services. The 

 water, in almost all these cases, is obtained by storing the excess of the 

 rain-fall (which would otherwise pass off from the surface of the land, 

 by the streams or rivers, during the rainy seasons) in artificial ponds, 

 provided with sluices, feeders, or main pipes, to conduct the water to 

 the placet where it is required. Under these circumstances the 

 dimensions of reservoirs, and the modes of their construction, must 

 admit of every imaginable variation ; but the general principles con- 

 nected with their formation may be briefly stated as follows. 



The reservoirs for feeding canals, or inland navigation, may be 

 made without much reference to the quality of the water to be stored 

 in them ; but those which are designed for the purpose of a town 

 supply must be made in such places as to obviate any danger from the 

 contamination of the water. It is customary that they should be 

 formed, in either of these cases, if practicable, in the gorges of moun- 

 tainous districts, where there might exist a large area of land having a 

 natural fall towards the outlet of the gorge. Writers upon meteorology 

 calculate that upon the average \ of the total rain-fall of the whole 

 year passes off by means of the superficial natural watercourses ; that 

 another { passes off by evaporation ; and that the remaining f, descends 

 into the ground to feed the land springs and the wells. In moun- 

 tainous districts, however, these proportions do not hold good; for, 

 firstly, it happens that, as a general rule, the nucleus of mountain 

 chains consists of dense impermeable rocks, which not only oppose the 

 infiltration of water, but also from the steepness of their escarpments 

 throw off the rain-fall in greater abundance than would be the case in 

 more level districts. Secondly, on mountains the rain-fall is usually 

 more abundant than it is on plains, and it is more evenly distributed 

 over the year; so that the natural surface of the ground does not 

 become so absorbent, nor docs the evaporation from that surface take 

 place with the same rapidity, as it would do in the low lands. It 

 thus happens that the quantity of water, which may usually be 

 calculated as being likely to find its way into a reservoir placed in a 

 mountainous district, may be reckoned as being about one half of the 

 total rain-fall; but the net quantity disposable will be often very 

 inferior to the quantity |thus originally impounded, because there must 

 always be an active evaporation going on from the water surface, 

 (which, moreover, will take place to the greatest extent when the 

 water is most wanted) and there must always be a more or less active 

 infiltration through the bed of the reservoir itself. As it will be 

 necessary to discuss the effects of these conditions of evaporation and 

 infiltration under the article WATKII SITI-LY, on account of their 

 influence upon gravitation water-works, it may suffice here to say that 

 it is very rarely indeed that the engineer ,can depend upon com- 

 manding more than from \ to J of the total quantity of the rain-fall of 

 hi* drainage area ; and that it is only exceptionally that he can attain 

 the higher limit above quoted. 



Another very important consideration will be found to affect the 

 dimensions of reservoirs, which has only been cursorily noticed above, 

 namely the distribution of the rain-fall over the year. In many cases 

 it is known that rain docs not fall for months together; and even in 

 the Bagshot Heath district droughts of four and five months duration 

 have taken place. A reservoir established in such a district must then 

 contain ; 1st, the total actual quantity required for the service it is 

 intended to perform ; and it is to be observed that during droughts 

 the consumption of water must be nearly double tliat which would be 

 required under normal circumstances, whilst the reservoir must be 

 made large enough to supply the largeit consumption, not the avenge 

 one. 2nd, it must contain, in addition to this quantity, enough water 

 to compensate for the evaporation and infiltration, and to secure the 

 water from injurious chemical changes. In fact the water of Urge 

 lakes even, unle;* constantly kept in motion by streams passing 

 through them, is liable to become vapid and deficient in n. 

 whilst pond waters, in dry, hot weather, become positively nauseous, 

 unless their volume should be very great indeed ; and vegetation, and the 



lower forms of animal life, develop themselves with singular activity 

 under the same circumstances. Of course this latter consideration 

 would not materially affect canal reservoirs, but it is an all impor- 

 tant one in the case of gravitation water-works, and the singular 

 story of the introduction of the anacliarit altintutrum into our canals, 

 proves that it is expedient to watch the growth of aquatic plants even 

 in canal reservoirs. 



In all descriptions of reservoirs it is important that precautions 

 should be taken to prevent the accumulation of alluvial matters of a 

 nature to fill them up; anil, in the case of water-works rem- 

 this is essentially necessary because the waters standing for a long time 

 over them must contract impurities from those matters. The nature 

 of the surface of the drainage area will regulate the nature of the 

 precautions to be taken ; for, if the soil should be one easily moved 1 >y 

 the surface rills, it will be necessary to form depositing pits on the 

 courses of the feeding streams ; on hard limestone, slate, or plutoiiic 

 formations, it may often only be necessary to prevent large boulder* 

 from being carried into the reservoir ; and on peaty uplands, it will 

 usually be found that the surface of the country will itself suffice to 

 prevent the transport of much alluvial matter. The water obtained 

 from peaty lands, it is to be observed, is not fit for the purposes of a 

 municipal supply; aid hitherto no satisfactory mode of removing the 

 qualities communicated to the water by the peat has been discovered. 

 For canal purposes peaty water is as good as any other, inasmuch at> 

 its colour and taste are of no importance for purposes of navigation ; 

 but either for irrigation, or for town supplies, such waters are 

 Inadmissible. 



In selecting the position for a reservoir the most important con- 

 ditions to be considered are, firstly, the nature of the bed; and 

 secondly, the position of the retaining wait The bed must not only, 

 as said before, be of a nature not to communicate impurities to the 

 water, but it must be for all practical purposes, impermeable. The 

 value of a reservoir, in fact, depends on its power of storing, tliat is to 

 say, of its holding water ; but when the strata of which its bed H 

 composed are so much fissured, or are of so permeable a nature as to 

 allow the water to escape, it becomes necessary both to increase tin- 

 original volume of the water stored, and to guard against the danger of 

 the water's finding its way under the seat of the dam. The con- 

 struction of the latter is, however, the most important part of the 

 works required for the formation of a reservoir, for the depth of water 

 against iti face frequently is not less than 40, or even 70 feet, so that 

 the pressure calculated to turn the reservoir over upon its outer edge, 

 or to thrust it forward horizontally, is enormous ; and the difficulties 

 of construction increase precisely in proportion to the height and the 

 length of the dam. Its position must therefore be selected in some 

 portion of the gorge to be converted into a reservoir where the sides 

 approach one another so as to contract the opening of the valley ; the 

 foot of the dam must be carried down far enough below the surface of 

 the ground or of any subjacent permeable strata, to prevent the lateral 

 passage of the water; its thickness must be made superior to that required 

 to resist any possible dynamical effort it may be exposed to ; the materials 

 of which it is composed must be able to resist the passage of water ; 

 it must be made high enough to prevent waves, by whatever cause 

 produced, from washing over its crown ; and finally the overflows, bye 

 washes, waste weirs and accessory structures (such as the sluices, draw- 

 off pipes, &c.) must be made perfectly water tight, unless in the parts 

 especially designed for the passage of the water. To secure the 

 condition of the impermeability of the seat of a dam it is often 

 necessary to carry the foundations as far below the surface as the dam 

 itself rises, and instances of foundations fifty feet deep are by no means 

 rare. Telford even recommended that when the strata on which a 

 reservoir had to be formed were of a porous nature, the whole of the 

 valley should be puddled ; so great an importance did he attach to the 

 necessity for opposing this dangerous action. 



The'Alams of reservoirs arc either formed of earthwork, or of 

 masonry, or of a mixed system of earthwork and masonry. Local 

 circumstances must guide the engineer in his selection of the precise 

 nature of the materials he will employ; but the result of careful 

 observations on the movements of large works of this description has 

 led to the general recognition of the following practical rules for the 

 thicknesses to be given. When masonry dams are used, it is found 

 to be necessary to make the thickness of the wall, .r, equal to the 

 following proportions of the height of the dam above the surface of 

 the bottom of the reservoir near its foot : 



at the top . x = h x 0-30 

 in the middle x = h x 0'50 

 at the bottom x = h x 070 



When earthwork is used the dam should be made fiom 15 to 16 feet 

 wide at the top, with slopes of at least 14 to 1 towards the water, 

 and of 2J to 1 on the dry side; the water side must be protected 

 against the abrasion of the waves by stone pitching, and below the 

 line of agitation its face must be carefully puddled. A wide puddle 

 trench, or a thick wall of hydraulic masonry, should be carried up in 

 the heart of the bank, and every precaution must be taken to resist 

 the passage of the water through the various layers of the body i.f I li 

 work. As a general rule the materials of the bank should be deposited 

 in layers of from to 9 inches in thickness, and well and carefully 



