FLOATING. 371 



would be prohibitive, owing to the large amount of compen- 

 sation involved, it may, nevertheless, be necessary to obtain 

 larger supplies of water for floating timber than the natural 

 course of a stream affords, and these may be secured by 

 constructing a tank. This is an artificial pond surrounded by 

 strong embankments, that is fed by underground culverts, or 

 by a canal bringing water from the upper part of the water- 

 course ; thus water may be collected in the tank to swell the 

 stream below it. 



There may be peculiarities of the locality that modify the 

 mode of construction of tanks, but in this respect they are much 

 less variable than dams. 



Figs. 241 and 242 represent a tank which has been con- 

 structed at Wilgartswiesen, in the Bavarian Palatinate. The 

 reservoir A is situated between the floating-stream t and a 

 small mill-stream m. It is surrounded by strong embank- 

 ments (d, d), 14 feet high, and is fed by the mill-stream, which 

 bifurcates from the watercourse above the reservoir and is led 

 along the hill-side with a gentle fall, so that at a it is about 

 10 feet higher than the watercourse, which it rejoins after 

 passing the mill M. There are sluice-gates at a and b, the 

 former for admitting the- water and the latter for its escape ; 

 s, s is a cart-road along which is conveyed the wood which is 

 stacked at h, and there put into the stream. This tank holds 

 280,000 cubic feet (8,000 cubic meters) of water, it can be filled 

 once daily, and takes 2 hours and 40 minutes to run dry, float- 

 ing 42,000 stacked cubic feet (1,200 cubic meters) of firewood. 

 The embankments of tanks may be of earth or masonry, or 

 half earth, half masonry, as shown in section in Fig. 242. 

 Here A represents the stone-masonry, B the earth-work, a the 

 sluice-valve, m the feeder, and t the watercourse. 



Tanks to assist floating have been constructed at several 

 places in Silesia, Franconia, the Palatinate, etc. ; they are 

 utilised in summer for irrigating meadows and cultivated 

 lands. 



v. Wt'irs. 



The works already described have for their object to increase 

 the quantity of water in a floating-channel, but as soon as the 



B B 2 



