1844.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



51 



2. If thp cuunlry slioukl decline towards the nioutli, as it commonly 

 does, it will be necessary tliat tlie banks of the drain towards the outlet 

 should be so much elevated as to equal the height of the highest part, 

 or the water that flows down will overflow and cause inundations. 

 Hence it is 



S. That the districts which have a great declivity on the surface 

 cannot have drains with gates, without overflowing the low lands 

 when they are closed ; and therefore in such a case we ought 



4. To separate the drains of the high lands (as far, at least, as the 

 highest flood of the river) from those of the lower grounds, and to 

 make the former discharge by an open month, enclosed with banks 

 suflSciently high to support the regurgitation of the river, while the 

 latter mav be provided with a gale and banks if necessary, in the 

 manner above named. It is true that if the water of the open drain 

 should not run in such abundance as to prevent the regurgitation of 

 the high waters, during the freslies, a deposit will be formed, and 

 there mav be so small a quantity of water in the drain, that it has not 

 sufficient power to remove the impediments when they are formed : 

 in this case new and repeated excavations will be required. 



5. The flood gale may be closed when the river is swollen, until the 

 water in the drain shall be raised to the same level, and then it may 

 be opened to discharge such additional water as may flow into the 

 drain; in this way the regurgitation of the flood will be prevented, 

 and the water that comes afterwards into the drain, will be discharged 

 without inundating the country. 



6. The low grounds may be drained by the use of flood-gates either 

 in rivers or in the channel above named, but more easily by the former 

 than by the latter, because the water of the river is lower than that of 

 the drain, and also because the deposit which is formed in the channel 

 cannot be produced in the river, in which the fall must consequently 

 be greater. 



The drains which fall into marshes, stagnant waters, and similar 

 places, have generally an open discharge, and the reason is, because 

 the difference between the highest and lowest surface of the water in 

 the marshes is, for the most part, not so great as to require the appli- 

 cation of a flood-gate (which is difficult to manage) to prevent re- 

 gurgitation; and especially as the fields which are to be drained into 

 them are higher than the surface of the marshes, and it is from the 

 fields that the water comes which swells them; besides which, on 

 deposit is to be feared from the regurgitation of the waters. Some- 

 times, however, the country has so little declivity in those parts con- 

 tiguous to the marsh, that remaining dry, the great part of the year, in 

 consequence of its elevation, it only spreads the waters at the time of 

 floods. Under such circumstances it may be useful to defend the 

 liigher groun<l by surrounding it with banks, so that the water of the 

 marshes increasing, may not overflow it, and at such times to arrest 

 the rain-water in tlie fields, which, when the surface of the water in 

 the marshes begins to fall, niay be discharged into it by one or more 

 cuttings in the bank. Such localities cannot be brought into a state 

 of perfect cultivation, being by nature marshy, but they must be kept 

 for pasture or meadows to vviiich the dampness of the soil is useful. 

 When marshes are occasionally much flooded, as, for example, when 

 rivers enter them, or when rivers overflow their banks, flood-gates 

 may be used at the mouth of the drains, but before they are intro- 

 duced, it is necessary to consider the duration of the floods, the state 

 of the country, and otiier similar questions, for upon these their use- 

 fulness depends. 



Those channels which have an immediate discharge into the sea, 

 must be differently treated according to their circumstances. The 

 rise and fall of the tides, and the swell produced by winds, is some- 

 times productive of damage, and sometimes of advantage to the 

 mouths of the drains. Every one knows that the sea forms its own banks, 

 and throws up mounds of gravel upon the shore. The height of these 

 defends ihe interior low grounds from inundatiun, which would other- 

 wise be the result in time of storm, and sometimes also at the time of 

 the usual high tides. These beaches must be cut lo form an outlet, 

 but the openings must, at the same time, he |irotected by strong 

 banks, in order that when the water of a stormy sea introduces itself 

 into the drain, it may not spread into the back country, and overflow 

 it for ever, as has sometimes happened in low grounds. Therefore 

 not to run such a risk, they are usually provided with strong gates, 

 which being shut when the sea is high, keep it within its ordinary 

 limits, and lieing opened when it is low, give a free discharge to the 

 water that was retained durnig their closure. In some drams, how- 

 ever, which, on account of their length, or-for some other reason, carry 

 a large quantity of water at all times, and are equal to small rivers, it 

 may happen that gates are not necessary, the continued flow of the 

 ■water of the drain being sufflcieiit to keep back the water of the sea; 

 nor are they necessary in those places where the country rises as it 

 recedes from the shore. By comparing the elevation of the sea vvhen 



tempestuous with the level of the country, it is easy to determine 

 what drains require gates, and what kind of banks should be employed. 

 There are some drains which have outlets so large and deep that they 

 form small harbours, and give shelter to vessels of moderate size. 

 This may be occasioned bv the natural depth of the sea in that situ- 

 ation, by the abundance of the water in the drain, or bv the position 

 of the shore ; it may arise from the direction of the mouth being sucli 

 that it is not exposed to those impetuous winds which, in tempest, 

 drive sand or beach to the coast, or from the great rise and fall of the 

 sea; or it may be occasioned by the operation of other causes, whicli 

 prevent the formation of a deposit, and promote excavation, but which 

 cannot be described without a particular examination of the place. 

 On the contrarv, the outlets of some other drains are closed wdien 

 certain winds blow, and these drains must either be diverted and dis- 

 charged in other places, or the water must be penned up so that it 

 may enter the sea with velocity, and remove the deposit formed at; 

 its mouth. 



In drains not large enough to have a good outlet, it is especially 

 necessary that they should be sufficient to carry all the surface water 

 of the country, and that they should not overflow their banks. It must, 

 therefore, be borne in mind, that as they have, under ordinary circum- 

 stances, a comparatively small quantity of water, they must, wdien the 

 stream is turbid, have a considerable fall before they can establish 

 their beds. In a plain of little declivity the bed would be elevated 

 above the level of the country, and the drain be rendered incapable of 

 receiving the surface waters. In streams of this kind it is useless to 

 expect any excavation, but it is, on the other hand, necessary to form 

 the channel by manual labour, and prepare the course the waters 

 should have to their discharge. 



We must then be careful that the channels shall be excavated suf- 

 ficiently deep to receive the water in great abundance, so that it may 

 not be raised above the plane of the conntrv, and, if possible, not 

 within the drains that run into them. In addition to this, every ex- 

 cavation is su|)erfluous, as, for the drainage of the land, it is enough 

 that the private drains should remain dry after the fall of rain. Such 

 benefits, however, cannot be obtained in low places with any amount 

 of excavation ; for, the bed being horizontal at a lower level than the 

 place of its reception, where the mouth of the conduit ought to be, 

 if greater excavations were made, they would only serve to produce 

 a greater regurgitation, or to cause an eddy ; besides which, when 

 the excavations are deeper, a greater width is required, which would, 

 in such a case, be a waste of ground, without a corresponding utility. 

 It is true, that in the excavation of these channels it is better that they 

 should be made too large than too small, for, although the drains of 

 the country carry only limpid waters, they must always hold some 

 earthy compounds brought from the surface of the cultivated land, 

 particularly at the time of heavy rains, or, if from nothing else, from the 

 cashing and breaking down of the banks of the conduit, and there- 

 fore, the water having but little velocity, in consequence of the little 

 declivity of the bed, as well as the small quantity of water, the earthy 

 m.ilters being deposited, must raise the channel. The water of the 

 drain being raised by the elevation of the bed, the surface waters of 

 the country can no longer have a free discharge : hence it is, that the 

 greater the excavation, so much the longer will it be before the bed is 

 raised to that height at which further deposition will become injurious; 

 but, on the contrary, if the first excavation be too small, the defect 

 will be immediately felt, and will continually increase. Hence it is, 

 that the drains not being able to maintain a free discharge, and being 

 necessarily obstructed by the inevitable accidents above mentioned 

 (besides m.iny others which ignorance permits, and malice creates) 

 repeated excavations are required, which must, as the occasion de- 

 mands, be done according to established rules." 



OCEAN STEAM NAVIGATION. 



Mr. Macqueen's Reply io lite Chairman and D/roclors of llic Royal 

 J\lail Sltam Packtt Company. London: Blackwood, 1S41. 



On a recent occasion, we expressed our regret that the condition 

 of oceanic steam navigation is so unfavourable, and that dissensions 

 exist which so seriously impede the extension of this important 

 branch of commerce, and deteriorate the property of shareholders. 

 Considered in a commercial point of view, ocean steam navigation 

 affords the means of acquiring for this country, an extensive transit 

 trade, if not ihe monopoly of it. We well know for how long a period 

 tl'.e supremacy ol Dutch commerce was maintained from such sources, 

 and how, in the present day, we are deprived of any shure of the 

 transit trade, and beaten out of the market by the Americans, and 



