Hydro-Electric Survey of India. Second Report on the Water Power Resources of India ascertained during the Season 1919-1920

The gross head in high and medium falls is the vertical difference in height between the point of application to the wheel and the water-level at the pile intake ; while for low heads the difference between the level of the head and tail waters must be taken. [...] 11 at the junction of these with the steel pressure pipes where the steep fall begins: The surge tank consists of a reservoir elevated to the level of the water where it enters the stave pipes connected by a largo pipe (or separate pipes) to the junction. [...] In the majority of cases of very low heads the power station is built across the river and the water flows directly through the strainers into the turbines. [...] " In order to prevent the channel being overfilled at the headworks a method often used is to place a diverting place in' the fairway at a point near the headworks such that any flow beyond the capacity of the channel is skimmed off and discharged-back to the stream. [...] (This of course assumes that the width of the sill is greatly in excess of the width of the channel.) The spill-way and scour valves of the reservoir should be near this point where most of the mud will collect.