DRAINING 



retically speaking, Ix 1 i-nlucrd to nothing ; for, ns it ex- 

 ceeds tlic bright of tin- water, it tin^ nothing to rcsi-l. 

 Hut it is frequently used as a foot-putti. and on the 

 slightest bank* cannot well be less than two feet. Six 

 fret is n more advisable hrcudth lor the h.mks of small 

 rivers. The dike* of Holland are 18 ells at top, and 

 an- used as roods. 



The inside slope of a li;>nk is of less importance. 

 About one foot of Ivi-e to one of pcrjx'ndicular is a pret- 

 ty natural slope for most earth ; but where faced with 

 sods, it may be much ^tt-i-jier. Some advantage is 

 thought to arise from making the fare of the bank con- 

 cave, as the settlement of the earth will l>o thereby les- 

 sened \\'e shall hereafter take an opportunity of gi- 

 ving the reader tin investigation of the principle^ on 

 which the form and thickness of dikes depend ; it is 

 n particular case of retaining Wall* for supporting 

 earth, running sand, or water. In the mean time, we 

 offer him the following from Silberschlag Theorit tics 

 Fteuvet, p. 72. 



Table of the Dimension* of Embankments. 



It is proper at all times to turf over the surface of an 

 embankment ; and should the exterior side be exposed 

 to waves or rapid currents, additional precautions be- 

 come necessary, as piles and planks of timber, or walls 

 of masonry. In the latter ease, it is highly useful to 

 Stop the open joints with heath :>nd moss, which col- 

 lect the silt, and lighten the dike ; but in most situa- 

 tions where these embankments are made, stones and 

 timber are of doubtful benefit, and the turf, being form- 

 ed on sandy soil, has little adhesion. 



Dutch me- The Dutch, our great masters in this art, were led, 

 thod of co- by many fatal accidents, to adopt a method of covering 

 the front of their sea-dikes in particular, which may be 

 called thatching them, with straw. The men employ- 

 ed for this purpose, kneel down on the bank, with their 

 backs to the sea, and have beside them bundles of straw, 

 of which they make ropes of an inch or two in thick- 

 ness. \Vhen they have twi-ted about a foot of this, 

 they press the middle into the snnd of the dike, by 

 means of a forked stick. The straw rope is then pro- 

 longed, and at the distance of about five or six inches 

 it i- pressed again into the dike; and thus they conti- 

 nue from the top of the dike to the bottom. Another 

 ro]K- is then worked in alongside of the first, and so on 

 long the bank, the ropes being laid as regularly and 

 rlose as in a Ix'e-hive. 



The quantity of straw consumed in this operation of 

 thatching the dikes ig, as may well be judged, \ery 

 great ; and magazines of it are everywhere kept in rea- 

 dinest, and regidar overseers are iii constant employ- 



to look after those structures on which Holland r> 

 dc|M-ii.l- for existence. 'The grass spring* up hctwi > n .TJJ" 1 



r.iw rope-, and after some time entirely conceals ^"JJ 

 them ; but they require frequent examination, and 

 whenever they are rotten must be immediately renew- 

 ed. A man covers alm.it S') feet per day. 



Bulwarks of stone are frequently employed as a fa- 

 cing for dikes, but very injudiciously, Ix'ing soon gul- 

 lied out and thrown down ( our.-cs of brick are em- 

 ployed with better effect, or a smooth covering of gra- 

 vel, the slope of the bank being made so gentle a^ to 

 admit the gravel to lie steadily. A \ITV ellectual facing 

 is also made by fascines, or faggots of brushwood. 

 Small osiers and aquatic brushwood planted along the 

 foot of the slope, are a good defence against ice. 



Where embankments are made on mossy soil, bog, 

 or soft fen, they should have a base sufficiently wide 

 between the ditches ; as we have -ecu for want of this 

 precaution, great lengths of dike overset or buried at 

 once, by the ditches bursting in. In such cases, tin- 

 soil, if possible, should be tinned by attrition, or warp- 

 ing by alluvial silt ; the counterd itches cut shallow and 

 at a CCKK! distance asunder, and if possible, they should 

 be allowed to run for sometime, so a*, in -omc cl, 

 to drain the ground ere the bank he completed. Should 

 this be impracticable, a thin wall of turf between a 

 double row of plank piling may do, until the interior 

 area be dry, and firm enough to" bear a stouter embank- 

 ment. 



The drainage of the embanked land is now to be 

 provided for : it is conducted upon the principles aj- 

 ready set forth. When an outfall sufficiently low can 

 be found, a back drain runs along the inside of the 

 embankment, until a proper opportunity occur of dis- 

 charging it. For that purpose it is sometimes necessa- 

 rv to convey the channel under the bed of the river it- 

 self, or some embanked branch of it, which is done by 

 means of a pipe of stone or timber, called a fox, or 

 culvert The form of these will be described in the ar- 

 ticle IM.\M) NAVIGATION. 



Where the embankment is only against floods or the 

 tide, an opening is made through the bank itself to 

 shut with a valve or floodgate against the exterior high 

 waters, and which being opened when they havr sub- 

 sided, permits the internal waters to escape. In cases 

 where this j* not practicable, the waters must be lilt- 

 ed by artificial means over the bank. 



Flood-gates are variously constructed : the simplest Floodgate* 

 for our purpose is a valve or clapper, hanging by the 

 top, and falling against the end of a pipe, or against a 

 sluice frame; at other times sluices or paddles are 

 made to slide up and down in a grooved frame ; and in 

 greater cases, butting gates are hung so as to shut 

 against each other in the middle like folding doors, or 

 to turn on a horizontal or vertical axis, by some of 

 which a body of water is at times collected and dis- 

 charged, so as to clear the month of the channel from 

 obstruction. When this outfall is situated on a shirt- 

 ing beach, it is often advisable to protect it by a 

 pier or jetty of piles, iS:c. and to remove the gravel or 

 sand which this may accumulate as often as appears 

 necessary, or to form .1 covered channel through the 

 whole line of l>each into deep water. Much may. how- 

 ever, be effected by the judicious position of the out- 

 fall, with respect to the currents, that it may not be 

 warped up by the depositions from the river 01 

 but rather swept clean. In dangerous cases, and expo- 

 sed situations, a second valve is sometimes formed on 

 the inside of the first ; and by the admission ot'a certain 

 4 



