GANGA 45th Issue | Page 8

an extent of area of more than 2000 ha

circular) or fern shaped (elongated). The

(20 sq. km.).

shape of the watershed controls the time

2. Watersheds based on drainage:

taken for the run-off to concentrate near

Drainage characteristics of a watershed

the outlet point. This time is known as

can broadly be related to its drainage

the time of concentration (tc). A fan-

pattern, stream density and drainage

shaped watershed provides greater flood

density. Drainage pattern is interpreted

intensity at the outlet, as all the

from the drainage map of the watershed.

tributaries are nearly the same. But in an

It depends upon the regional geology

elongated

and pre and post structural control over

concentration for each tributary is

the catchment area. Stream density is the

different, and the discharge at the outlet

number of streams in the watershed per

is distributed over a long period and as

unit area (sq. km.). High stream density

such probability of inundation in the

is an indication of high inundation of the

catchment area is remote.

terrain. Drainage density, on the other

4. Watersheds based on other criteria

hand, is the total length of all the stream

From

channels per unit area (sq. km.).

watersheds may be categorized into

Drainage density indicates the drainage

several types like, (i) hills or flat

efficiency of the basin. A higher value of

watershed

drainage

well-

gradient, (ii) humid or arid watershed

developed network and high run-off

depending upon overall climate of the

causing intense flood, while a long value

area, (iii) red soil or black soil watershed

(less than 4km/ 1sq. km.) indicates

based on general soil character and type

relatively moderate to low run-off and

of the area etc.

density

indicates

a

watershed,

management

based

the

point

on

time

of

of

view,

topographical

higher permeability of the terrain and
less chances of inundation due to flood.
3. Watersheds based on shape :-

Editor- Sujit Choudhury, Published by
IRBMS (© Integrated River Basin
Management Society)

Watershed are broadly categorised in
two groups, either fan shaped (nearly
8

Integrated River Basin Management Society