§ 185. _Total and Available Fall._--Let H_t be the total difference of
level from the head-water to the tail-water surface. Of this total
head a portion is expended in overcoming the resistances of the head
race, tail race, supply pipe, or other channel conveying the water.
Let [h]_p be that loss of head, which varies with the local
conditions in which the turbine is placed. Then