86 BULLETIN 126, U. S. DEPARTMENT OF AGRICULTURE. 



in the discussion cited. The greater the surface width of the water 

 in the channel at the time the ice is formed the greater will be the 

 tendency for the ice sheet to bulge upward and thus relieve the side 

 thrust. Again, the flatter the side slopes of the channel the greater 

 will be the upward component of force parallel to the lining surface 

 and accordingly the less will be the thrust normal to its surface. Of 

 course there are many reasons for limiting the flatness of the side 

 slopes, but in the design of concrete-lined canals for use in localities 

 subject to low temperatures, and particularly where winter operation 

 is necessary, the benefits resulting from flattened side slopes should 

 not be overlooked. 



ACKNOWLEDGMENT. 



The grateful acknowledgment of the writer is hereby tendered 

 to the engineers and managers of irrigation enterprises and to the 

 field members of this division who have assisted in collecting reliable 

 information pertaining to the subject treated. He is especially 

 indebted to S. T. Harding and Justin T. Kingdon for able assistance 

 rendered in compiling the data and computing the tables contained 

 in this report. 



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