THE TORRENTS OF SWITZERLAND. 51 



the water of a stream is turned from its old channel into the new one 

 that has been prepared for it, the operation is generally very gradu- 

 ally performed, so as to enable the water to fill up the old bed as 

 much as possible by depositing its silt. 



A plan pursued with much success is that of building out from 

 the high bank of a stream (which it is desired to confine into a nar- 

 rower channel) insubmersible spurs, stopping at the points where the 

 new bank is to be situated. The water flowing in between these 

 spurs deposits its dirt and gravel, and gradually builds up the new 

 bank. In many cases the ends of the spurs are connected by low 

 artificial banks of masonry over which the water flows. These banks 

 retain and protect the deposits, and, when the latter have attained a 

 sufficient depth, the artificial banks are raised to their permanent 

 height. Still another method pursued with the same object in view 

 is that of starting up stream and building the banks to their per- 

 manent height until a point is reached where it is desired to " fill." 

 Here the artificial banks are left temporarily very low. The water 

 overflows them, and the reduction of its velocity entails the deposit 

 of its silt. When this has continued as long as necessary or prac- 

 ticable, the walls are raised to their permanent height along the 

 section and the same process is repeated below. This gradual process 

 is also very advantageous from a financial point of view. When the 

 engineer finally reaches the mouth of the stream at one of the lakes, 

 we should expect to find his difficulties at an end, as the lakes are 

 usually so deep that the alluvion makes little impression on them, 

 and their areas are such that floods are not much to be feared. But 

 he is confronted here with a new difficulty, that of anchoring or 

 securing the foundation of his artificial river bank. The soil is 

 generally alluvial over a large area, and is very damp. He generally 

 has to terminate the masonry before he reaches the less stable alluvial 

 soil and continue the structure by means of wooden material, which 

 retains its position much better under such circumstances and is 

 more cheaply replaced. It would be natural to imagine that man's 

 control of the water problem stops at this point. But not so with the 

 Swiss; he even controls its exit from some of the lakes. This is 

 notably the case at Geneva, where by means of ingenious dams the 

 lake is maintained at what is deemed a proper level. When it is 

 remembered that this lake is fifty miles long by ten broad, an idea is 

 gained of the amount of water controlled. Every few years the 

 level is lowered for a given period, so that repairs may be made to the 

 walls and structures along the shores. 



