I 



FARMERS' REGISTER. 



305 



channel is straighter than the old one (to say no- 

 thing of other obstructions) water runs much 

 taster in a straight channel than in a windh 

 although the banks might be perfectly smooth, 

 and gradually curving; tor, when water runs-in a 

 right line, the hindermost particles push the lore- 

 most ones along straight before them; but in a 

 curvilinear, or angular one, the hindermost parti- 

 cles push the ibremost ones to one side out of the 

 way, and the latter having to turn entirely round, 

 describing a circle, and then following on, are re- 

 tarded in their motion. This is the reason of those 

 little whirlpools, at the edge of the swiii. part ol 

 the stream, next to the eddy parts. In the old 

 channel there are nine large sudden curves, be- 

 sides numerous smaller ones, which are avoided 

 by straightening the channel. In the last bend, 

 the old channel runs at right angles with itself, 

 where it rushes against the j bank, which 



is fifteen feet perpendicular, which in freshets, 

 would dash the water over the land this 

 side, which of course would break over the low 

 grounds on the other side of the old channel, be- 

 tween this bend and the mouth of the ditch: 

 which is a small piece of flat squared out between 

 this part of the old bed, and a steep hill, running 

 within a few yards of the mouth of the canal, 

 which was formerly subject considerably to inun- 

 dation, and ought to have been appended to the 

 figure. The curvilinear form of every channel, 

 shows how much a current is opposed to 

 tions, for let these bends be as sudden as they 

 may, they always turn by a gradual curve, instead 

 of an angle; hence if one stream be let into ano- 

 ther at rjght angles, it will soon change itself more 

 suilable to the direction of the main stream. 



Fifthly. It is plain that the stream is freed from 

 a great many obstructions which retard the velo- 

 city, besides the bends of the channel, which 

 like so many dams, obstruct its progress, over 

 and through which, it breaks, to the injury of 

 crop and land. Hammocks, (formed by trees 

 thrown across or falling into the old channel, logs, 

 rafts of wood, sticks and trash of every descrip- 

 tion, bushes growing on the banks, &c.) are con- 

 stantly turning the stream out of a straight course, 

 which it is ever seeking. The current now runs 

 where there are neither stumps nor trees (on 

 which account too, it was more easily excavated.) 

 As to those obstructions winch belong both to 

 straight and sinuous channels, such as come un- 

 der the head of pressure, friction, &c. — these are 

 overcome in a good measure, by all those causes 

 which increase the velocity of the current in its 

 new channel. 



Thus we have shown how the velocity is accel- 

 erated in the new channel, and the reason for it; 

 from which it seems it must be more than doubly 

 increased. Now as the discharge of water is as 

 the velocity, the canal must discharge in the 

 same time, more than double the water of the 

 old channel. This rapid discharge prevents the 

 accumulation of water in the channel, out of 

 which it breaks, and inundates the land. And 

 what water is supplied by tl is drawn off 



much faster, and of course the stream is down 

 much quicker. This discharge of water is further 

 increased by enlarging the capacity of the chan- 

 nel, which is the effect also of the velocity of the 

 water, to which the washings, in depth and width, 

 and the ca.vi.il}'.- o!'{ ho sides, arc always in propor- 

 Vol. Ill— 3!) 



tion, for which there is abundant authority. "The 

 increase of velocity [in a stream,] increases the 

 action on the sides and bottom, in consequence of 

 which the width is augmented, and sometimes al- 

 so, but more rarely, the depth"." — Gregory. 



"A velocity of three inches per second, at the 

 bottom, will just begin to work upon the line clay 

 lit for pottery, and however firm and compact, 

 will tear it up." — Du Buat. 



"A velocity of six inches will lift fine sand — 

 eight incites will hit sand as coarse as linseed — 

 inches will sweep along fine gravel — twen- 

 ty-lour inches will roll along round pebbles, an 

 inch in diameter, and it requires three feet three 

 in hes per second at the bottom, to sweep along 

 shivery angular stones, of the size of an egg." — 

 on an Rivers. 

 There is no danger of a canal of this sort wash- 

 ing aqd caving too much, a notion which with 

 has obstructed this branch of draining. The. 

 laws which fix limits to channels, are as certain 

 and immoveable, as the hills themselves. The 

 current and the channel will always adapt them- 

 selves to each other, until they become permanent. 

 The effect is produced in this way. As it is the 

 ■' ,1 velocity of the water which increases 

 the depth and width of the channel, so it is the 

 dinflflfaition of this velocity which stops the wash- 

 ing and caving. The velocity of the water in the 

 canal will diminish in proportion to the enlarge- 

 ment of the area of the section of the canal, rep- 

 resented by Fig. 2; or to speak more in the style 

 of hydraulics, "when the sections of a river vary, 

 (the quantity of water remaining the same,) the 

 mean velocities are inversely as the areas of the 

 sections." — (Gregory. ,) That is. as the channel 

 widens, (the quantity of water) the depth dimin- 

 ishes, and of course the hydrostatic pressure di- 

 minishes, and the water spreading over a wide 

 bottom, the friction increases, and the velocity of 

 the stream diminishes. Now if a freshet comes, 

 a swift current is formed in the middle of the 

 stream, and the water next to the sides of the 

 ditch is more of eddy: the swift, particles of water 

 push the eddy ones to one side, and these being 

 loaded with sand and mud; and the sur- 

 face of the stream being convex, as represent 

 ed in Fig. 2, which is represented byjhe curve 

 line (t a w) they roll towards the sides, where 

 they deposite the mud and sand. The reason of 

 this convexity of the surface of streams, which 

 may be seen by putting the eye on a level with 

 the. surface, is that the water in the middle, at the 

 surface of a stream, is swifter than towards the 

 sides and bottom, bein« - farthest removed from 

 friction, and being swifter, it loses some of its 

 weight and rises, and being retarded too by the 

 eddy water on each side which it meets with, r 

 accumulates in the middle. The surface in the 

 of some rivers, is three or four feet abovr 

 the edges of the water at the sides; hence a loose 

 boat floats to the bank. The sand and mud are 

 ed, while the stream is falling. Mud is al- 

 ways deposited by eddy water, and sand by run- 

 ning water. The mud suspended in the water is 

 carried off by the swiftness of the current, while 

 the sand is let fall. But where the wafer is still, 

 the mud has time to precipitate. This is the rea- 

 son why the clay is deposited on the edges, and 

 the sand at the bottom. In long dry spells when 

 th locity of the stream is weakened, it gradu- 



