Book III. EMBANKMENTS. 715 



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. 



4333. 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. 



4 84. The best construction of tkejiood-yate 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 bit it) ; but not so closely or tight as to stick when swelled by moisture. 

 To prevent this, as well as to give it additional tightness, its edges should not be square, but should bevel 

 somewhat inward in 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. The floodgates or self-acting sluices, at Bar Loch embankment fall against a flat 



surface. (fig.6Si.) A writer in the Perth Miscellany states, (vol. i. p. 41.) 

 664 that many of the tunnels in the embankments of the Tay have only 



p-r/W/ss'/vv /t,. t h/'jmi.j - wooden valves with iron hinges, and a lid of lead or iron nailed on for 

 J : weight to keep them down. These, he says, are not to be depended on, 



and he has accordingly had some tunnels made of two inch plank with the 

 end cut at an angle of 4"i° for the valve, and placed on a slope of 8 inches 

 in 18 feet, the water being discharged on a broad piece of pavement. He 

 had an iron plate " cast the exact size of the mouth of the tunnel, and 

 about half an inch thick, with holes drilled two inches apart, and three- 

 fourths from the edge of the plate, for riveting a piece of saddler's leather, 

 or shoemaker's brown sole, which extended at least two inches beyond the plate, and covered the whole 

 end of the tunnel, the upper end of the leather nailed to the wood serving as hinges, and the edges of 

 the mouth previously lined with the same material. Thus the strength of the tide never raises the 

 valves, and completely prevents the water from getting in." (p. 42.) 



4335. 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 water from every dip and hollow place as 

 it collects, and thus free the surface effectually from stagnant water ; saving such only as may be wanted 

 for the use of pasturing stock. 



4336. If alien waters have a natural and accustomed channel through the embanked 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 time of floods. Where it is found that an outlet cannot be had low 

 enough to free 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. 



4337. Jin 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, may be 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 rapidly discharged ; by which 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. Where 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. 



Subsect. 2. Different Descriptions of Banks in general Use for excluding Waters. 



4338. Mounds or banks for excluding rivers or the sea are generally formed of earth, but 

 sometimes also of masonry and even of wood. Embankments of common earth are 

 sufficient fcr resisting occasional floods : if this earth be loose, the bank will require to 

 be spread out at the base, at the rate of one foot and a half or two feet horizontal for 

 every foot in height ; that is to say, a bank of loose earth three feet high will require to 

 be nine feet or twelve feet broad. If the earth to be made use of is a compact clay, or if 

 turf of a solid and compact body can be procured, the slope of the bank may be much 

 steeper, according to its height and the depth of water which may be expected to press 

 against it. 



4339. The earthen wall (Jig. 665.) is the simplest description of embankment, and is 



frequently erected by temporary occupiers of 



f 65 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, bat 

 rarely, overflowed or inundated ; and is set out 

 z&T in a direction generally parallel to the river or 



'" "~ shore. Its base is commenced on the sur- 

 '''^MmM&M^^^i^^^™^^''-''^ face, from two to five feet wide, regularly built 

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

 tilled up with loose earth. The wall is carried up with the sides bevelled towardb the 



