FLASHBOARDS 93 



The ends of the different sections overlap each other, as seen 

 in the illustration, and a fairly water-tight joint is thus provided by 

 utilizing the water pressure itself. For sealing the joint between 

 the lower edge of the boards and the masonry it has been found 

 that a composition of cinders and straw, well mixed before appli- 

 cation, is very satisfactory. In it the cinders form the body, while 

 the straw is the elastic tightening medium. 



While the pins are ordinarily removed once a year, the flash- 

 boards are likely to be taken up a number of times each season, 

 and speed and economy in their handling is, therefore, of impor- 

 tance. For wide streams the usual method of handling them is by 

 means of a scow provided with a steam-driven derrick, while for 

 narrower streams specially designed cableways with chain hoist 

 have been used with very great success. 



Sliding Gates. These may be either of the plain friction type 

 or they may be provided with roller guides to make their operation 

 easier. 



The gates used by the Mississippi River Power Company at 

 Keokuk, Iowa, shown in Fig. 44, indicate probably the maximum 



FIG. 44. Spillway Gates. Mississippi River Power Company, 

 Keokuk, Iowa. 



size to which the friction type can be built. They are 11 feet 

 high and 32 feet long over all. Each gate consists of a frame- 

 work of 18-inch I-beams, covered with f-inch steel plate on the 

 upstream side. The edges are milled to make a water-tight joint 

 with the iron sill plates against which they fit, and the gates are 



