Drainage Basin

A drainage basin is a specified land area surrounded by a divide, so called because it is a line of separation that divides the precipitation that falls on two-adjoining basin and directs the ensuing runoff into one or other river system.

Quantative study of geomorphic manifestations or morphometry is helpful in defining on basin and for a meaningful comparison with any other basin. A drainage basin may be defined by a set of its drainage characteristic, which may be grouped under 1. Linear aspects 2. Areal aspects and 3. Relief aspect. Which enables understanding of their functional relationship with runoff thus providing a scope for predicting runoff for different meteorological inputs.

LINEAR ASPECTS

Stream order

Strahler’s (1957) ordering, which was modified upon that of Horton (1945) was followed for determining the stream order. According the smallest un branched stream segments is called as of first order. The First order stream segment join together to from a second order.

Stream number

Stream number is number of stream segments of each order and it presented it graphical form

Bifurcation ratio

This is ratio between the numbers of segment of a given order to the number segment of the next higher order. The weighted bifurcation is marginally higher in inter-basin areas.

Stream length

Here the lengths of various stream segments were measured and mean lengths of each order of stream were computed.

AREAL ASPECTS

Drainage Area

This is the entire area drained by a stream.

Shape

The shape of a basin is the main factor on the discharge pattern. In general log and narrow basins are having low discharge compared to other shape.


Elongation ratio (Re)

This is ratio of the diameter of basin and the maximum length of the basin

Re = (2Au) / Lb. Max.

For a circular basin, this value is nearly one.

Infiltration number

Infiltration number of a drainage basin is defined as product of drainage density and stream frequency.

Infiltration number= drainage density ´ Stream frequency

Drainage density is the cumulative mean length of streams per unit area.

Stream frequency is the number of stream segments per unit area.

RELIEF ASPECTS

In the maximum basin relief (h) is the elevation between the basin outlet and highest point on the perimeter. The relief ratio is indicative of the intensity of the erosion processes.

Rugged number

It is defined as the product of the basin relief and its drainage density