356 WOOD TRANSPORT BY WATER. 



2. Improvement and Maintenance of Watercourses for 

 Floating Wood. 



No watercourse is constantly fit for floating without some 

 artificial improvement, but all streams are not susceptible of 

 the same amount of improvement ; in many cases the low 

 value of the timber to be floated will not allow of much 

 expenditure at a profit in this direction, and sometimes the 

 forester has to put up with the mere maintenance of the 

 natural state of a stream. Hence, the works on no two 

 streams used for floating resemble one another. In the 

 following pages the most perfect methods of improving and 

 maintaining a floating-channel are described, so that the 

 forester may select what is practicable in any particular case. 



The improvements consist of : increasing the head of 

 water in a stream according to requirements, beyond its 

 average quantity ; regulating the course of a natural stream ; 

 constructing 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, etc., 

 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 neces- 

 sary. 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 

 occurrence, especially in high mountain-ranges with masses of 

 snow and glaciers, where lakes of different sizes are frequently 

 found in the upper stages of the side-valleys. These per- 

 manent water reservoirs are very valuable, for they usually 



