Book 111. 



CHANGING THE COURSES OF RIVERS. 



721 



water, so as to render it difficult to get a proper foundation for a pier. Where the 

 foot of the injured bank is covered with a pool at low water, shelve oil' the brink of 

 the bank, and shoot down loose stones from the top of it ; suffering them to form their 

 own slope, in the action of falling, and by the operation of succeeding Hoods . continuing 

 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 greater magnitude. 



4367. Jf'/icn the channel of a rapid river is narrow, and the banks undermined and washed awav bv 

 the ton ents, what Marshal terms the land.guard is to be used. 



4368. Informing a land-guard for this purpose, lie 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 with. 

 out 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 be laid, with a gently rising slope, until thev 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 awav 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 rammer, 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 splinters 

 of stone are to be driven in, as wedges, to increase the firmness, and prevent the current from tearing out 

 an unguarded stone. It follows, of course, that the largest and longest of the stones ought to be used 

 where the greatest resistance is known to be required. 



4369. The repairs of a bulwark of this sort, like every other species of river fence, require to be 

 attended to from time to time, especially after great floods. If the foundation 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 wedged in afresh, or their place supplied by others. 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. Changing the Courses of Hirers, deepening their Beds, or raising their Waters 



to a higher Level. 



4370. A river whose course is in a straight line, or nearly so, hardly ever makes any en- 

 croachment on its banks, except perhaps very large rivers, when they rise above their usual 

 level, either by an increase in their own waters, or from 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.) 



4371. The alteration of the course of a river or brook is attended with difficulty and 

 expense, according to the particular circumstances. In a simple case, in which one 

 straight cut only is required, the principal difficulty, 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 difficulty may be said 

 to vanish. The mouth of the new cut receives the current with a straight course ; con- 

 sequently, 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 channel : 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. 



sM&xi worn 



673 



4372. An entirely new 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 old 

 bed, its action on surfaces 

 which are so different in re- 

 gard to induration ends, if 

 great care is not taken, in 

 holes and gulleys in the new 

 bank, which require to be con- 

 stantly filled up with loose 

 stones thrown in, and left to 

 be fixed by the pressure and 

 motion of the water. In the 

 case of a river passing near a bouse (fg. 673. ) this is sometimes of great importance. 



4373. Cutting the new channel is merely a work of manual labour ; being attended with no other diffi- 

 culty than what may arise from the expense, which will depend on the size of the river, the nature of 

 the ground to be cut through, and the value of labour in the given district. It is mostly to be ascertained 

 with sufficient accuracy by previous calculations. (See 3323.) 



4374. The size of the new cut, on account of its greater depth, may be small, compared with that of the 



3 A 



