EMBANKMENT. 



away of the banks in some places 

 and the deposition of mud in others, 

 more skill and more expensive works 

 are required to keep it within its 

 banks and to prevent the effects of a 

 rapid current in destroying them. In 

 tiiis case strong piles arc driven deep 

 into the ground, and, instead of earth- 

 en dikes, stone walls are opposed to 

 the force of the water. 



" The embanking of a considerable 

 river often requires the course of the 

 stream to be changed, and instead of 

 the winding course which rivers nat- 

 urally take through plains, straight 

 channels are artificially made for 

 them. At first sight it would seem 

 that a straight channel is the natural 

 course of a stream ; but this is far 

 from being the case : a straight course 

 can never be maintained without ar- 

 tificial means ; water never flows in 

 straight lines, but always in curves. 

 The slightest inequality in the bottom 

 or sides partially obstructs its course, 

 and produces a circular motion in the 

 water ; and this, acting on soft banks, 

 soon hollows them out, which, in- 

 creasing the eddies, accelerates the 

 change in the current. When a river 

 is turned into a new channel, the 

 banks must be strengthened with 

 piles of masonry, and the foundations 

 of the works must be laid below the 

 gravel or stones which may have ac- 

 cumulated, that they may not be un- 

 dermined by the percolation of the 

 water. 



"When the dikes are only intended 

 to check the waters at the time when 

 they flow over their natural banks, it 

 is best to raise them at some distance 

 from the river on each side, and par- 

 allel to its course ; because, in sud- 

 den floods, the water, having a great- 

 er space to flow through, will not rise 

 so high, and will sooner recede. The 

 natural banks must be carefully at- 

 tended to in this case, that they may 

 remain nearly the same, without be- 

 ing subjected to that continual change 

 which we have noticed before. Those 

 who have long attended to these 

 changes and their immediate causes 

 will find no difficulty in checking them 

 in the outset by very easy and simple 

 253 



means. Whenever a bank begins to 

 be undermined, a few piles driven in 

 judiciously, and some stones thrown 

 into the river above the place where 

 its banks begin to wear away, will 

 cause a change in the current, and 

 throw it over to the opposite side. 

 Indeed, if this is done injudiciously, 

 the banks opposite will begin to wear 

 away ; but by continued attention, 

 and prevention rather than correc- 

 tion, any river having a moderate cur- 

 rent may be kept within its proper 

 bed. 



" It sometimes happens that rivers, 

 near their mouths, form shallow es- 

 tuaries, and occupy much ground 

 which might be usefully employed. 

 In this case an entirely new outlet 

 may sometimes be made, through 

 which the river may at once dis- 

 charge itself into the sea ; and the 

 whole course will probably be soon 

 filled up by the deposition of soil and 

 mud brought in by the tides ; for it is 

 the current which clears the channel, 

 and when this is taken away the chan- 

 nel soon fills up. In the course of a 

 short time the old mouth of the river 

 will be so filled up as scarcely to ad- 

 mit the tide ; and an embankment 

 across it may lay a large fertile tract 

 of land quite dry. 



" Where embankments are made 

 against the sea, greater skill is re- 

 quired to resist the force of the waves. 

 If there are materials at hand to lay 

 a bank of stones imbedded in clay, 

 with a broad base, and the sides slo- 

 ping very gradually upward, a very 

 safe barrier may be opposed to the 

 waters. It is not the direct impulse 

 which is the most destructive : waves 

 striking against a sloping surface lose 

 their force and rise over it ; but it is 

 in returning that they draw the ma- 

 terials with them, and scoop out the 

 foundations. If the stones are well 

 joined together, the retiring wave will 

 have no effect in loosening them ; but 

 if any one of them can be singly re- 

 moved from its place, they will soon 

 disappear one after another, till a 

 breach is made ; after which a single 

 storm may destroy the whole embank- 

 ment. In various places the ingenu- 



