64 THE IMPROVE.MKXT (>/' KIVERS. 



and brush of all sorts are utilized for dike-building and bank protection. In some 

 localities wood or brush is formed into gabions or baskets which are filled with heav\ 

 material, such as gravel or stone, or an envelope of poles is bound together and similarly 

 filled. Dikes are also built of solid stone masonry on some of the rivers of Eurojx;, 

 and concrete has been used for similar purposes in America. 



Sections. The front and back faces and also the coping of a dike should be so 

 constructed as to withstand the erosive action of the current. A simple ridge of broken 

 stone, wide at the bottom and decreasing in width as it rises, with its top paved with 

 stone of large size and irregular shape, is widely used. In another form, when the 

 water is not deep, the river-bed is excavated to the desired depth in two parallel trenches, 

 and these are filled with broken stone carried up to or above low-water level. This 

 leaves a core of river-bed material between the two walls, and this is paved with heavy 

 stone as are also the walls themselves. This paving is sometimes made in the form 

 of a curve rising some distance above low water. Where the water has considerable 

 depth the two parallel ridges of stone are placed on the natural bed so that their inner 

 slopes will meet at the bottom. The V-shaped space between them is filled with a 

 cheaper material, such as gravel. On top of this, as a base, additional stone is placed 

 to bring the structure to the proper height. 



There are several forms of dikes composed of timber and stone, in addition to the 

 crib-dike heretofore mentioned. Sometimes a single row, sometimes a double row of 

 piles is driven into the bed and the piles connected by wales, and stone is piled 

 around them, generally up to low water. The portion of the dike standing above 

 low water is then planked up. When there is a considerable tendency to undermining, 

 which takes place more or less along the faces of ah 1 dikes, and especially where their 

 orientation approaches a direction normal to the current, sheet-piles are frequently 

 used, and these are also protected below the water-line by broken stone. 



Construction. The general process of constructing broken-stone dikes is to dump 

 the stones loosely into the water from barges, the line of the dike being indicated by 

 piles driven at intervals into the river-bed. These piles serve also to afford convenient 

 moorings for the barges. The stones are left with a natural slope. When the river- 

 bed is soft the action of the current will cut part of it away, causing the riprap to sink. 

 In the course of time, however, it will become stable and the dike will take a curvilinear 

 form with a wide base. To prevent any after-movement the foundation is sometimes 

 prepared in advance of the construction by dredging out the material to a desired depth. 



The settlement which takes place renders it advisable that the coping be loosely 

 put down, so that it may accommodate itself to the movements of the dike. If it is 

 closely placed and the dike should sink, the paving may fall in irregular piles leaving 

 portions of the dike exposed to the current where they cannot be seen and repaired 

 until the low-water season comes. This coping or paving should be of very heavy 

 stones, not only in order to withstand the force of the current but also to successfully 

 resist the pressure from ice-gorges. The main body of the dike may be made up of 



