For a long time the energy contained in water runoff has been beneficially exploited. Initially this was accomplished by direct conversion into mechanical energy, but with the advent of electricity about a century ago, conversion has shifted predominantly to electricity generation to take advantage of this flexible and versatile energy form. Early hydropower schemes were small in size to conform to the relatively small power markets available. It was soon realized, however, that considerable economies of scale could be achieved by exploiting larger river flows. This realization went hand in hand with the development of electric power transmission, which permitted large and dispersed power markets to be supplied from a single scheme. Smaller schemes tended to fall out of favor because their relatively minor contribution to the demand coverage did not seem to justify the financial and infrastructural efforts involved to bring them to fruition.