CONCEPT OF MINIMUM SPECIFIC ENERGY AND ITS RELATION TO NATURAL FORMS

Abstract

It is proposed to show in this paper that there is a solution to the problem of non-uniform flow and this solution not only explains in detail many land forms which occur naturally, but thereby, yields a definition of 'form' loss. If a channel, in which the transverse distribution of specific energy is uniform, converges and/or diverges, and the bed changes so that the flow will be critical at all cross-sections at the same time, the channel appears to be close to being hydraulically smooth. Many natural forms, particularly estuaries, are readily explicable in this way. The most obvious one is the bar at the mouth of a river. It follows, if the river enters the sea with reasonable uniform grade, which most rivers do, the bed must rise as the flow loses the restricting influence of the banks (i.e. the width increases) if constant specific energy is to be maintained. It is possible to calculate with considerable accuracy the dimensions of useful structures based on this concept. A large number of full size but nevertheless experimental structures have been built making use of the resultant benefits which develop:- low turbulence, accurate differential water levels and a clearly defined flow pattern, allowing very considerable savings to be made by eliminating expensive protective works.