360 WATER-TRANSPORT. 



The improvements consist in : — increasing the head of water 

 in a stream accordinpf to requirements, beyond its avera^^e 

 quantity : regulating the course of a natural stream ; construct- 

 ing an artificial channel to replace it, and booms to stop and 

 collect the floated material. 



(a) Increasing the Head of Water in a Stream. 



Besides rivers such as the Inn, the Isar, the Oder, ^c, 

 which are constantly used for timber-floating, nearly all 

 German mountain-streams require arrangements for raising the 

 average height of their water. It is especially the higher parts 

 of streams, near their sources, where this is most necessary, 

 for there they contain the least amount of water, and pass 

 through forest areas where floating is most necessary. The 

 means used for increasing the water are : — lakes and ponds, 

 feeding-canals, dams and tanks. 



i. Lakes and Ponds. 



In valleys and mountain-depressions at a high elevation, 

 natural reservoirs such as lakes and ponds are of frequent occur- 

 rence, especially in high mountain-ranges with masses of snow 

 and glaciers, where lakes of difterent sizes are frequently found 

 in the upper stages of the side-valleys. These permanent water 

 reservoirs are very valuable, for they usually lie along the line of 

 floatage, and by means of a simple sluice at the outlet of a water- 

 course from a lake, the level of the latter may be maintained 

 high enough to furnish a good head of water for floating wood 

 down the stream. Many lakes are thus utilized. 



A small lake from which a side-stream passes into the line of 

 floatage, or which may be connected with it by a canal, may also 

 be similarly utilized, and in both these cases the dams to be con- 

 structed are similar to those which will be described further on. 



ii. Ff(diu<i-Canals. 



Instead of lakes and ponds, watercourses near the floating- 

 channel may be utilized to raise the water-level of the latter 

 by leading their water into it. A mountain-side, through the 

 principal valley of which the floating-channel passes, is often 



