7w; 



PRACTICE OF AGRiruI-TlRE. 



P 



III. 



666 



centre, so as to finish in a width of one foot or eighteen inches, at five or six feet in height. 

 Collaterally with such walls, and at the distance of three or four feet, a small open drain is 

 formed, as well to collect the surface water of the grounds within, as that which in time 

 of lioods will necessarily ooze through a wall of this construction. The water so col- 

 lected is let through the wall by tubes, or tunnels of hoards, with a valve opening out- 

 wards on their exterior extremity. When the (low of water from without approaches, it 



shut', the valve, which remains in this state till the flood subsides, when, the height of the 



water within being greater than that without, it presses open the valve and escapes. 



Walls and valves of this kind are common enough in the drier parts of the fenny districts 



of Lincolnshire and Cambridgeshire. 



4340. The cart/ten mound (Jij. 666.) is the most general description of embankment, 



and, as it is executed at considerable 



expense, is only undertaken by such 



as have a permanent interest in the 



soil. This barrier applies to sea 



lands overflowed by every spring 



tide, and to alluvial plains inundated by every flood. It is set out in a direction parallel 



to the shore, and to the general turns of the river, but not to its minute windings ; and 



it is placed farther from or nearer to the latter, according to the quantity of water in time 



of floods, the rapidity of the current from the declivity of the bed, the straight course of 



the stream, and the intended height of the bank. The two sides of such a mound are 



generally formed in different slopes. That towards the land is always the most abrupt, 



but can never be secure if more so than 45° ; that towards the water varies from 45° to 



15° ; the power of the bank to resist the weight of the water, as well as to break its force 



when in motion, being inversely as its steepness. The power of water to lessen the 



gravity of bodies, or in other words, to loosen the surfaces over which they flow or stand, 



is also lessened in a ratio somewhat similar. 



43+1. The formation of the earthen mound consists merely in taking earth from the general surface of 

 the ground to be protected, or from a collateral excavation, distant at least the width of the mound from 

 its base line, and heaping it up in the desired form. The surface is then in general cases covered with 

 turf, well rolled in order to bind it to the loose earth. The earth of such mounds is generally wheeled 

 in barrows ; but sometimes it is led in carts placed on a wooden roller instead of wheels, which, with the 

 treading of the horses, serves in some degree to consolidate the bank. 



4342. The excavation serves the same purposes as the open drain in the earthen wall ; and similarly 

 constructed sluices or valves are introduced on a larger scale. Sometimes, also, the interior water is 

 drawn off by windmills, and thrown over the mound into the river. This is very common in Hunting, 

 donshire, and might be greatly improved on by employing steam engines for entire districts, one of which, 

 of a ten horse power, would do the work of twenty mills, and this in calm weather, when the latter 

 cannot move. 



4343. Embankments of this description are the most universal of any, and their sections vary from a scalene 

 triangle of ten feet in base, and three feet in height, as on the Forth near Stirling, and the Thames at 

 Fulham, to a base of 100 feet, and a height often feet, as in the great bank of the Ouse, near Wisbeach. 

 The great rivers of Germany and Holland are embanked in this way, when so far from the sea as to be 

 out of the reach of the tide; as the Vistula at Marienwerder, the banks of which, near Dantzic, are 

 above fifteen feet in height ; the Oder, the Elbe, Sec. All these banks are closely covered in every part 

 with a grassy surface, and sometimes ornamented with rows of trees. 



434+. Near the sea, where such banks are washed by every tide when the course of the wind is towards 

 the shore, and by all land floods and spring-tides, grass is only to be found on and near their summits. 

 The rest of the bank is bare, and to preserve it from the action of waves, currents, and the stones, 

 pieces of wood, and other foreign matters which they carry with them, the surface is covered with gravel, 

 reeds, or straw kept down by pieces of wood ; faggots, wicker hurdles, nets of straw ropes, straw ropes 

 laid side by side and fastened, or handfuls of straw fixed in the ground with a dibber (Scale's Travels 

 in Germany, SfC chap, i.), or any other contrivance, according to the situation, to prevent the washing 

 away of the batik. It is common to attribute to these coverings the power of breaking the force of the 

 waves ; but this power depends, as we have already stated, on the slope of the bank and its smoothness; 

 and the use of the surface covering, and of the constant attention required to remove all obstacles which 

 may lie loft on it by floods and tides, is to prevent the loosening power of the water from wearing 

 it into holes. For this purpose, a sheet of canvas or straw-netting is as good, whilst it lasts, as a covering 

 of plate iron or stone pavement. 



4345. All banks whatever require to be constantly watched in ti7>ie of floods or spring-tides, in order to 

 remove every object, except sand or mud, which may be left by the water. Such objects, put in motion 

 by the water, in a short time wear out large holes. These holes, presenting abrupt points to the stream, 

 act as obstructions, soo n become much larg er, and if not immediately filled up, turfed over, and the turfs 

 _,,,_ y ! A S. pinned down, or the new turfs ren. 



/ N. deredbysomeothermeansnoteasily 



softened and raised up by the 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 (uxhaven, and along the coast of 

 I, incolnsb ire, are regularly watched 

 throughout the year ; the surface 

 protection is repaired whenever it 

 goes out of repair ; as is the body of 

 the bank ir. the summer season. 

 4346. The mound with pvd- 

 a die watl. ! Jig. 661 .) It gene- 



■ rally happens that the earth of 



such banks is alluvial, and their foundation of the same description ; but there are some 



