CHAPTER III 



CLASSIFICATION OF DEVELOPMENTS 

 LOW-HEAD DEVELOPMENTS 



WATER-POWER developments may be divided in two broad 

 classes: First, low-head and second, medium and high-head. 



To the former class belong those plants which consist of a dam 

 which creates pondage at the point where the water is to be utilized, 

 so that the water passages to the turbine units will be compara- 

 tively short while the quantity is large. The chief items com- 



FIQ. 25. Map Showing General Lay-out of Pennsylvania Water and Power 

 Companies, Development at Holtwood, Pa. 



prising the head works of such a development are: The dam with 

 its spillway, the forebay, the intake and the tailrace. 



Typical plants of this kind are shown in Figs. 25 and 26. 

 A dam extends across the river and impounds a large body of 

 water above it. It is built with a spillway section for the entire 

 length, this being necessary on account of the large flood dis- 



70 



