Book III. 



EMBANKMENTS. 



649 



Ct 



water, will end in a breach of the bank. A similar effect is produced by a surface formed 

 of unequal degrees of hardness and durability. The banks of this description in Holland, 

 at Cuxhaven, and along the coast of Lincolnshire, are regularly watched throughout the 

 year ; the surface protection is repaired whenever it goes out of repair ; as is the body of 

 the bank in the summer season. 517 



4024. The mound with pu d- 

 dle wall {Jig. 517.) It generally 

 happens that the earth of such 

 banks is alluvial, and their 

 foundation of the same de- 

 scription ; but there are some 

 cases where the basis is sand, 

 silt, or gravel; or a mud or 

 black earth, as in some parts 

 of Cambridgeshire and Lin- 

 colnshire, which does not easily 

 become so compact. Here it 



is cornmon, before beginning " ' . 



the bank, to bring up what is called a puddle-ditch, or section 6f clay (a), in the centre 

 of the highest part of the mound in the direction of its length, and of three or five feet 

 wide, according to the depth of the stratum of silt (6), and the intended height of the bank 

 (c). When the clay of this puddle-ditch is well worked, either by men's feet or clay 

 rammers, the bank will be perfectly impervious to water, and if against a mild stream or 

 shore, need not contain such an accumulation of earth as where the imperviousness of the 

 bank to water depends chiefly on the mass of materials. As already observed, the 

 important point to attend to in this variety of mound is, to found the section, or 

 wall of clay, so deep as to be in contact with a stratum (a) either by induration ; or its 

 argillaceous nature, impervious to water. 



4025. Mounds with reversed slopes. In some cases of embanking rivers, as where they 

 pass through parks, it is desirable to conceal, as much as possible, the appearance of a 

 bank from the protected grounds. Hence the mound is simply reversed, the steepest 

 side being placed next the water. It is proper to observe, that such banks are not so 

 strong, by the difference of the weight of the triangle of water which would rest on the 

 prolonged slope, were it placed next the river, and are more liable to be deranged in 

 surface in proportion to the difference of the slopes, the water acting for a longer period 

 on every part of the slope. , 



4026. Mound faced with stones. This is the same species of mound, with a slope 

 next the water of forty-five or fifty degrees, paved or causewayed with stones or timber. 

 In Holland this pavement or causeway is often formed of planking or bricks ; but in 

 England generally with stones, and the mortar used is either some cement which will 

 set under water, or, what is better, plants of moss firmly rammed between them. The 

 objection to such banks -are their expense, and their liability to be undermined invisibly 

 by the admission of the water through crevices, &c. They are, therefore, chiefly used 

 where there is little room, or where it is desirable to narrow and deepen the course of a 

 fiver. 



4027. Mound protected by a wicker hedge. This is a Dutch practice, and, where 

 appearance is no object, has the advantage of not requiring watching. Wicker-work, 

 however, subjected to the strain of waves, will be obviously less durable, than where it 

 lies flat on the ground, and can only decay chemically. This wicker hedge is sometimes 

 a series of hurdles supported by posts and studs ; but generally in Britain it is a dead hedge 

 or row of stakes, wattled or wrought with bushes presenting their spray to the sea or river. 

 Besides placing such a hedge before a bank, others are sometimes placed in parallel rows 

 on its surface ; the object of which is to entrap sand, shells, and sea weeds, to increase 

 the mass of mound, or to collect shells for the purpose of carrying away as manure. 



4028. The sea ivall {fig. 518.) is an embankment 

 formed to protect abrupt and earthy shores or banks of 

 rivers, and consists of a wall, varying in thickness, and 

 in the inclination of its surface, according to the re- 

 iquired height, and other circumstances. Belidor, in his 

 Traite de Hydraidique, has given the exact curve which 

 the section of such a wall ought to have (a, 6), in order 

 to resist loose earth, and which is somewhat greater than . 

 where the earth behind the wall is supposed to be chiefly ~ """ 

 firm. Some fine examples of such walls, for other purposes, occur in the Caledoniax 



- Canal, and perhaps the finest in the world are the granite walls which embank the Neva 

 at Petersburgh, the construction of which may serve as an example of a river cased 

 with stone on a foundation of soft bog earth. 



