Ch. 10] 



SPILLWAY STRUCTURE 



183 



paters; therefore stilling basins are used extensively. Foundation re- 

 quirements are similar to those for any gravity clam. 



Side-channel spillways similar to Fig. 3 require extensive founda- 



Max. pool 

 _EL346^ 



Ma x.F.C.pool 335 



Max. power pool EI.330 

 Min. power pool EI.305 



Grout-^ ^Foundation 



curtain 



drain 



Mil] 

 I I I I I k 



Foundation^ 

 drains 



Fig. 1. Gravity spillway, Clark Hill Dam. Foundation is massive granite gneiss. 



Frequent operation. 



Max.pool EI.573 



To p power pool EI.520" 



Max.tailwater El.497.6 



Min.tailwater EI.422 5' EI.432 

 I r\ i rv 



"** ^Foundation drain Slab anchored to 



rock by tie rods 



Fig. 2. Gravity spillway, Whitney Dam. Foundation is argillaceous limestone. 



Frequent operation. 



Grout - 

 curtain 



tion investigations because their satisfactory performance depends to 

 such a great extent on the stability of the rock. Deep cuts into the 

 abutment are conducive to minor slides, and the steep side walls are 

 subject to creep and spalling during construction. These minor geo- 

 logic factors are difficult to evaluate from explorations, and as a re- 



