532 



ANNUAL. REPORT SMITHSONIAN INSTITUTION, 1923 



these level changes are illustrated in the diagram, while the changes 

 in effective head on the turbines is plotted immediately below. 



Full lines above show the level changes of the high-level basin; 

 dotted lines below, those of the low-level basin. Starting at low 



$ ^ S 3 2~ 



water, you will note that for 2.35 hours the level of water in the low- 

 level basin is unchanged, for the water from the tailrace is dis- 

 charging into the tidal supply direct, but during this time the head is 

 decreasing from 28y 2 feet to 13!/2 feet when it becomes expedient to 

 discharge into the low-level basin, when the head will at once rise to 

 27V2 feet. 



