FLOATING. 



379 



or vertical banks of a stream, if not of hard rock, get under- 

 mined and fall in, holes being formed in which the wood 

 sticks ; or the material of the bank may be carried away and 

 form an obstruction lower down the stream. Wood wiiich 

 lodges against the bank becomes at length waterlogged, and may 

 be lost. Hence, all bad banks require facing. Wherever the 

 bank is composed of mere earth, a slope of 25° to 30' 

 should be given to it, and it should be sodded or planted with 

 willow-cuttings to give it firmness. If a current sets in 

 against such banks they may be protected by wattle-work, a 



Fig. 220 



trench being dug along the bank, and a wattle-work fence 

 constructed, and the interval then refilled with earth well 

 rammed-in. The earth bank may also be faced with ordinary 

 stone-masonry, or merely with large dry stones, and the trench 

 filled with broken stones or gravel. Where stones are scarce, 

 fascines may be laid parallel to the bank, secured by means of 

 stakes, and covered alternately with stones or earth. 



Other modes of protecting banks consist in a row of piles 

 which are driven -in, in front of the place to be protected, 

 and either bound with wattle-work, or planks or fascines 

 fastened on inside them (fig. 220). Where wood is plentiful 

 the w^alls may be of logs 4 to 6 inches thick (fig. 222), supported 

 by stakes (a), and nailed together with long iron nails. It is, 

 however, always better to employ stone-masonry for the purpose 

 wherever stone is procurable ; both to economise timber, and 

 because the latter is not durable. Where stone is used for the 



