Book III. EMBANKMENTS. 647 



materials that impound them. They cannot, by loosening the obstructing matter, as 

 nature would otherwise direct them, force their way through it ; nor by surmounting it, 

 can they wear down a channel, and thus set themselves at liberty. 



4011. In ordinary cases, the outer floodgate may be guarded by a pile fence or jetty, 

 run out from the foot of the embankment, across the known drift of the beach ; and in 

 such a manner as not to interrupt the outfall channel of the water ; the gravel, &c. which 

 such a safeguard may accumulate, being removed from time to time as occasion may 

 require. 



4012. The best construction of the floodgate for the uses now under consideration is the 

 common valve, hingeing at the top, swinging outward and falling into a rabbeted frame. 

 In forming and hanging a floodgate of this construction, there are a few particulars 

 worthy of attention. It should be made of seasoned wood, and ought to be double; the 

 boards or planks of which it is formed being made to cross each other, to prevent its 

 casting. It should fall truly, and fit neatly within a surrounding rabbet (to lessen the 

 power of the waves to lift it) ; but not so closely or tight as to stick when swelled by 

 moisture. To prevent this, as vrell as to give it additional tightness, its edges should not 

 be square, but should bevel somewhat inward iw the manner of a bung ; the rabbet in 

 the frame being made to answer it. In fixing the frame, it ought to be suffered to lean 

 or batter inward ; in which position the door will shut closer, and be less liable to the 

 action of the waves in an exposed situation than it would if it were hung perpendicularly. 

 It ought not, however, to lie so flat or heavy as to prevent the free escape of the internal 

 waters. 



4013. The internal waters which rise within or fall upon the area of the embanked 

 lands, are to be collected by a main drain, continued upward from the floodgate ; and 

 furnished with branches to spread over every part of the field of improvement, so as to 

 draw the ivater as it collects, from every dip and hollow place, and thus free tlie surface 

 effectually from stagnant water ; saving such only as may be wanted for the use of pas- 

 turing stock. 



4014. If alien waters have a natural and accustomed channel through the emfeanked 

 area, it may be found necessary to raise a suitable bank at a proper distance on each side 

 of the stream ; in order to prevent its overflowing the area in times of floods. \fTieJ'e it 

 is found that an outlet cannot be had low enough to ^ree the area entirely from surface 

 water, it is requisite (though no alien waters intrude) to form an embanked channel or 

 reservoir ; to gain the required outfall, and to throw the waters which lodge on the lower 

 grounds into this receptacle ; by a draining mill, of which there are a great variety of 

 constructions. 



4015. An embanked channel, if the banks are raised high enough, or are placed wide 

 enough asunder, so as to contain a sufficient body of water, may have a further use ; 

 which, in some cases, maybe of the highest importance to an improvement of this nature. 

 For, by the help of folding floodgates, such as are commonly seen in use for the locks of 

 navigable canals placed at the lower end of this canal or reservoir, a body of water may 

 be collected and rapidlyMischarged ; by whicli easy means, not only the channel of the 

 outer drain, but its mouth, if judiciously contracted, may, from time to time, be cleared 

 from obstructions. Whefe alien waters of a good quality pass through the field of im- 

 provement, an embanked channel may be profitably applied in watering the lands; and 

 where alien waters, which have not a natural or fortuitous passage through it can be 

 commanded, and conducted to it at a moderate expense, they may prove highly beneficial, 

 for either or both of these purposes. 



Su RSECT. 2. Of the different Descriptions of Banks in geiieral Use for exclucUng Waters. 



4016. Mounds or banks for excluding rivers or the sea are generally formed of earth, but 

 sometimes also of masonry and even of wood. 



4017. The earthen wall {fig. 514.) is the 

 simplest description of embankment, and is J^^M ^^^ 

 frequently erected by temporary occupiers of 

 lands on the general principle of enclosing and 

 Subdividing, which is sometimes made a condi- 

 tion of tenure between the landlord and tenant* 

 This wall applies to lands occasionally, but 

 rarely overflowed or inundated ; and is set out .^^ 

 in a direction generally parallel to the river cr 

 shore. Its base is commenced on the surface from two to five feet wide, regularly built 

 of turf on the outsides, with the grassy sides underneath. The middle of the wall is 

 filled up with loose earth. , The wall is carried up with the sides bevelled towards the 

 centre, so as to finish in a width of one foot or eighteen inches at five or six feet in height. 

 Collateral to such walls, and at the distance of three or four feet, a small open drain is 

 formed, as well to collect the surface water of the grounds within, as that which, in time 



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