Formation of delta-shaped river basin

__NOTOC__The formation of a river basin at the mouth of the river is usually characterised by the shape of a delta, the triangular Greek letter. The cause of this shape of the river basin may be explained by the theory of colloids.

Introduction

The river basin does form due to the formation of bottom-set beds, consisting of finer materials carried farthest seaward and laid down on the floor of the embayment, on which the delta is formed. Fore-set beds are somewhat coarser and they represent the advancing front of the delta and the greater part of its bulk. They usually have a distinctly steeper dip than the bottom-set beds and are in reality a continuation of the alluvial plain of which the delta is the terminal position.

Application of Colloidal theory to delta–shaped river basins

Colloids are such substances, which basically possess an outward force which expands in two ways: -1. Ordinal (vertical pressure)2. Abscissal (horizontal)

The lattice spread around those s controls these forces. In the ordinal force the pressure is maximum at the two apexes of the particle. In the case of abscissal pressure, the maximum pressure is at the vertex which depends upon the lattice.(fig 1) In the formation of delta-shaped river basin, the abscissal pressure is much more than the ordinal pressure(fig 2)Therefore the delta shaped river basin is produced.

Colloids are present in the river system due to the presence of suspended alluvial silt as well as silica deposits from the seawater, which act as the lattice for the colloidal bed.

Examples of delta shaped river basins

The Delta (shaded area) of the St. Clair River in Lake St. Clair has the classic shape of the delta (see fig 3)

ee also

* River delta