Book III. 



CHANGING THE COURSE OF RIVERS. 



653 



to pour them down, until the bank be secured, at least from minor floods, and then 

 slope back the upper part, to give freedom to floods of higher magnitude. 



4042. When the channel of a rapid river is narrow and the banks undermined and 

 washed away by the torrents, what Marshal terms the land-guard is to be used. 



4043. Informing a land-guard for this purpose, he says, the foundation should be laid 

 pretty deep, to guard against any accidental scoopings from the floods. The wall ought 

 to be carried up dry, or without mortar, the stones being laid with their ends outward, 

 their inner ends pointing to the same centre, like those of an arch, and to be backed with 

 gravel, or earth, rammed in firmly behind, as the facing is carried up. The coping or 

 uppermost course of the stones is to be securely bound, with thick tough sods (8 or 10 

 inches deep), whose surfaces, when beaten down, ought to lie even with that of the stone- 

 work; and similar sods require to belaid, with a gently rising slope, until they unite 

 smoothly with the natural turf of the land to be defended ; so that the waters of floods, 

 when they rise above the stonework, may have no abruptness to lay hold of, but may pass 

 away smoothly over the surface of the land, as they commonly do over smooth greensward, 

 without injury. Finally, the stones are to be beaten forcibly into the bank, with a ram- 

 mer, a mallet, or a small battering-ram, adapted to the purpose ; thus rendering the whole 

 compact and firm, to resist the current. Where vacancies or fissures still appear, long splin- 

 ters of stone are to be driven in, as wedges, to increase the firmness, and prevent the cur- 

 rent from tearing out an unguarded stone. It follows, in course, that the largest and 

 longest of the stones ought to be used where the greatest resistance is known to be required. 



4044. The repairs of a bulwark of this sort, like every other species of river fence, re- 

 quire to be attended to from time to time, especially after great floods. If the found- 

 ation be laid bare, it requires to be re-covered with rough gravel, or with stones thrown 

 loosely against it. If any of the facing stones be displaced or loosened, they are to be 

 replaced with others, or to be wedged in afresh. Or, if the turf which binds them at the 

 top be disturbed, the torn part should be cut out square, and be firmly and completely 

 filled up with fresh turves. 



SuBSECT. 2. Of Changing the Course of Rivers. 



4045. A river whose course is in a straight line, or nearly so, hardly ever makes any en- 

 croachment on its banks, unless perhaps in very large rivers, when they rise above their 

 usual level, either by an increase in their own waters, or their flow being in some degree 

 interrupted by the tides. Hence, whenever a river is narrow in its channel, and winds 

 considerably, any mischief it commonly occasions may be prevented by deepening and 

 straightening the course of the stream. {Code of Agr. p. 319.) 



4046. The alteration of the course of a river or brook is attended with diflSculty and ex- 

 pense, according to the particular circumstances belonging to it. In a simple case, in 

 which one straight cut only is required, the principal diflSculty, and that which requires the 

 best skill of the artist, lies in directing the current of the first flood, out of the old into 

 the new channel. But if a bend of the old channel can be made use of, this diflSculty 

 may be said to vanish. The mouth of the new cut receives the current with a straight 

 course; consequently, "if it be made of sufficient capacity, the river, in a flood, can have 

 no propensity left towards its old channel : and the loose materials which rise in forming 

 the mouth of the new cut, will generally be sufficient to turn the stream at low water into 

 it. But if a suitable bend cannot be approached by the new cut, a directing pier will be 

 required to bend the flood current, and give it a straightforward course into the new chan- 

 nel : a watertight dam being formed between the point of the pier and the firm bank of the 

 new channel to prevent the water from regaining its wonted course. 



4047. An entirely neio bed or 

 channel, however, is much to 

 be preferred where it can be 

 obtained; for in an altered 

 course, when the stream passes 

 alternately through new soil 

 and through a part of its oldbed, 

 its action on surfaces which 

 are so different in regard to 

 induration ends, if great care is 

 not taken, in holes and gulleys 

 in the new bank, which require 

 to be constantly filled up with 

 loose stones thrown in, and left 

 to be fixed by the pressure and 

 motion of the water. I n the case 

 of a river passing near a house 



(Jig. 521.) this is sometimes of considerable importance. 



521 



