408 



THE FARMER'S MAGAZINE. 



beads of rivers must be assimilated to the straight liiie, by 

 using the largest circular sweep that can be got, and the 

 barriers that are presented to an inpinging current must not 

 ofiFer a direct resistance, but receive the force in a shaq-) 

 divergence, and throw ofif the brunt of the violence. This 

 adoption forms an approach to the straight line ; and though 

 not straight itself, it throws the water into a straight course) 

 till it meets a similar obstacle, when it is similarly treated. 

 In making new courses for water, or improving old ones, it 

 is a great blunder to confine the current. Water spread 

 abroad is very harmless, and damage arises from large col- 

 lections that are confined in the movement, and agitated in 

 the course. A tendency must ever be manifested to widen 

 rather than contract the beds of rivers, and to straighten 

 the lines of course wherever a possibility exists. Necks of 

 land may be often cut through with advantage, in order to 

 obtain a straight course, even at a present sacrifice in the 

 land that may be used. The gradual damages of future 

 waste will reach the amount, and exceed the present ex^ 

 penditure. 



The action of floods of water over a level surface of ground 

 is not violent, nor the force very large ; the intrusion is 

 easily averted, and the direction controlled. The bank lies 

 in the direction of the course of the river, and has only to 

 support the weight of a fluidjbody that glides along its ex- 

 terior, but does not exert an action upon its constructed 

 strength. It has only to show the course to the water, and 

 not impede or obstruct it; the outspread water is restrained, 

 but not carried any prescribed course. The bank must be 

 directed along its course, bo as to avoid any abrupt turning 

 or hollows, in which water can lodge, and press with weight. 

 The exterior slope must be convex, and the line must be 

 uniformly gradual in the bendings, and afford the water an 

 easy rolling motion, without any ripple, or displacement of 

 the particles. Care must be used that the embankment 

 is continued to the first current of the overflowing, in 

 order that the water does not get behind the mound, and 

 render it of less avail. 



In alluvial countries, aa now described, the surface is flat, 

 and the currents of water are slow, and hence the means of 

 preventing damage are adapted to these qualities. Rivera of 

 greater or less magnitude, that flow from hilly countries, are 

 rapid in the course from the fall of the ground, and liable to 

 very sudden risings of water by meaus of heavy rains in the 

 mountains : the impetuous course continues till the flat coun- 

 try is reached, and before that advance much damage is done 

 by the raging waters rolling against the banks, tearing away 

 the loose soil in the narrow alluvial valleys through which the 

 river flows, which very often amounts to a total alteration of 

 the course, when a bed of gravel is left for the new channel 

 that is taken from the cultivated land. These hilly grounds 

 and narrow valleys produce more bendings than happen in 

 wide plains, and the soil being mostly alluvial in earths and 

 gravels, the waste is easy, and the demolition very quick. The 

 gravel that is rolled along by the torrent is usually heaved 

 against one side of the channel, which being obstructed, the 

 water is driven to the other side, and with the whole force and 

 weight it undermines and tears the soft deposit of which the 

 banks are formed. The power of the water is very much aug- 

 mented by the narrow channels which are formed between the 

 natural banks, and the mounds of rolled gravel, which shifts 

 with the floods and lies where deposited; 



The funous rush of these impetuous torrents requires to be 

 opposed by the strong erection of very hard materials. Solid 

 stone work is the best resistance, built of squared blocks, with 

 or without mortar, and raised beyond the highest reach of the 



waters. The form of the bulwark is square, and longer in the 

 face to the river than in the breadth to the land, and must be 

 very firmly based on the solid substratum that is reached by 

 digging through the alluvial mass of gravels and loose earths- 

 The barrier is called a jetty, and is placed to receive the cur- 

 rent of the water at a sharp angle of divergence, and to throw 

 it oflf easily, and almost without seeming to stop the direction 

 of the current. An obtuse angle of divergence will throw the 

 force of the water against the opposite bank, and if the bed o^ 

 the stream be narrow, the water will break it, and probably 

 cause a damage equal to that which is sought to be prevented. 

 The jetty must throw the current of water into a mid-channel 

 and not against either bank, and consequentlj^ the face of the 

 stone work must be in a straight line with the mid-channel 

 into which the water is wished to be directed. The force of 

 the current being broken against the jetty, the water will flow 

 for some distance before a new force is acquired, unless the 

 fall of the country is very great ; and when a fresh current is 

 formed, which threatens danger to the bank, a jetty is there 

 built, which turns the stream, as before, into a mid-channel, 

 and clear of either bank. In this way the stream is conducted 

 in a harmless current till it reaches the placid flow of the level 

 country, when it is directed by the embankments that have 

 been described. 



It is useful to protect jetties in front, when the streams of 

 water are very powerful, by placing large stones in a loose 

 position at the base of the wall, and raised to the height of the 

 ordinary quantity of water. The bottom of the heap may 

 extend three or four yards into the stream, and taper to one 

 stone at the top where the loose aggregation leans against the 

 jetty. The weight of each single block must be sufficient to 

 secure for itself an immovable bed, and defy the force of the 

 water to change the position. In the substrata of clay and 

 alluyial earths strong and lengthy timber piles may be driven 

 into the bed of the stream, as has been mentioned before, and 

 a defence formed between them and the jetty ; but in many 

 cases the driving of piles is difficult, and the loose aggregation 

 of stones will be preferred. Both ends of the jetty must taper 

 backwards into the bank with a wall like itself, in order to 

 prevent at the upper end the ingress of water behind the 

 building, and at the under end the eddying of the stream 

 into a corner, which may become the receptacle of waters that 

 may seek a new channel. The whole volume of the stream 

 must be directed into a mid-channel, and without any scatter- 

 ing of the sheet of water towards either of the banks. The 

 collected stream will wear a channel for itself by the weight 

 of the volume, and for that purpose every encouragement 

 must be given to direct it in a mass. This direction is very 

 peculiarly applicable to streams that descend an alluvial valley 

 from higher grounds, where the banks are in composition soft 

 and easy of demolition, and where the rapidity of the torrent 

 soon excavates a bed for the water. It is not here meant to 

 confine the bed of any river of water, but in certain cases to 

 direct the body of water in a mid-channel, which will keep it 

 from running against the banks and tearing away the land. 



Water-courses are beds of rivers on a small scale, that 

 traverse estates, farms, and plantations on their way to join 

 the main rivers that lead to the ocean. A surface of undu- 

 lations and sinuosities very often compel a tortuous course 

 of the waters ; and a formation of gravel or of soft alluvial 

 ground gives way to the floods and torrents that run in the 

 bended course that has been executed. These torrents arise 

 from the heavy falls of rain and melting of snows, and are 

 confined in doing harm at the bending of the course by 

 driving into the ground with heavy mallets a row or two of 

 strong stakes at one or two feet distant, and weaving a fence 



