It must be emphasized that the full application of the above and other
more sophisticated equations requires further reading (e.g. Ackers, 1983;
Garde and Ranga Raju, 1985; Graf, 1984; Vanoni, 1975), and the equa-
tions are quoted here only to demonstrate the correlation and trend.
Thus, although the relationship between the transport of bed sedi-
ment and the flow and even the relationship between the hydraulic resis-
tance and channel sedimentary features, particularly the bed configuration
(which in turn is a function of sediment characteristics and discharge), are
broadly known, the third required equation for alluvial channel computa-
tion, relating the flow parameters and the erosive resistance of the banks,
still by and large eludes a physically based formulation. Nevertheless, the
minimum stream power concept or other optimization methods show most
promise in this area, where we otherwise fall back on régime equations
(Section 8.3) which synthesize the physical functions into groups of formu-
lae describing the channel geometry (Ackers, 1983).
8.3 River morphology and régime
River morphology is concerned with channel configuration and geometry,
and with longitudinal profile; it is time dependent and varies particularly
with discharge, sediment input and characteristics, and with bank material.
River morphology can be substantially influenced by engineering works,
although this influence is not necessarily beneficial. Natural river channels
are straight (usually only very short reaches), meandering, i.e. consisting of
a series of bends of alternate curvature connected by short, straight
reaches (crossings), or braided, i.e. the river divides into several channels
which continuously join and separate. The various stages of a schematized
river (de Vries, 1985) are shown in Fig. 8.1.
RIVER MORPHOLOGY AND RÉGIME 327
Fig. 8.1 Schematized river (after de Vries, 1985)