Contents preface (VII) introduction 1—37

7
HYDRAULICS OF ALLUVIAL
CHANNELS

7.1. GENERAL
Civilisation prospered in agricultural lands by the side of rivers. From the beginning of civilisation, mankind has given attention to the problems of rivers. The boundaries of many rivers consist of loose material, which may be carried by the water flowing in these rivers. Depending upon the prevailing conditions, the loose material may either get deposited or scoured. Thus, the boundaries of such a river channel are mobile and not rigid. A change in discharge of water flowing in a rigid boundary channel will cause a change only in the depth of flow. But, in case of mobile (or loose) boundary channels, a change in discharge may cause changes in cross-section, slopes, plan-form of the channel, bed forms and roughness coefficient. The application of the theory of rigid boundary channels to loose boundary channels is, therefore, not correct. Evidently, the problem of mobile boundary channels is more complicated.
The bed of a river channel generally consists of non-cohesive sediment (i.e., silt, sand, and gravel) and such rivers are called alluvial rivers.
Sediment (also known as alluvium) is defined as the loose and noncohesive material through which a river or channel flows. Sediment is also defined as fragmental material transported by, suspended in, or deposited by water or air, or accumulated in the beds by other natural agents. Ice, logs of wood, and organic materials flowing with water are excluded from the definition of sediment.
A channel (or river) flowing through sediment and transporting some of it along with the flowing water is called an alluvial channel (or river). The complex nature of alluvial channel problems stands in the way of obtaining analytical solutions, and experimental methods are generally adopted for obtaining solutions of problems to alluvial channels.