THE DRAINAGE SYSTEM

The drainage system is an integrated system of tributaries and a trunk stream which collect and tunnel surface water to the sea, lake or some other body of water. The total area that contributes water to a single drainage system is known as a drainage basin. This is a basic spatial geomorphic unit of a river system, distinguished from a neighbouring basin by ridges and highlands that form divides. Thus, river basins are natural units of land. They are regarded as the fundamental geomorphic as well as hydrological units for a systematic study of the river basins, mainly due to the following three reasons:

(i) They can be placed in an orderly hierarchy,

(ii) They are areal units whose geomorphological and hydroloical characteristics can be measured quantitatively, and

(iii) They can be treated as working systems with energy inputs of climatological variables like temperature and rainfall and output of river discharge as runoff.

The Committee on Runoff of the American Geophysical Union treats the micro-unit within a river basin as the watershed, while the sum of all the micro, meso

and macro tributaries of a river is known as a river hasin.