INTRODUCTION

India is country of rivers. More than 400 big and small rivers are found in India, which are further divided into 23 large and 200 small river basins. The flow of water through well-defined channels is known as drainage and the network of such channels is known as drainage system. The drainage pattern of an area is the result of the geological time period, nature, and structure of rocks, topography, slope, etc. The drainage of the Indian subcontinent has adjusted itself with the evolution of three main geomorphological entities, namely the Northern Mountains, the Northern Plains and the Peninsular Plateau. About 77% of the drainage area consisting of the Ganga, the Brahmaputra, the Mahanadi, the Krishna, etc. is oriented towards the Bay of Bengal. On the other hand, 23% comprising the Indus, the Narmada, the Tapi, the Mahi, and the Periyar systems discharge their waters in the Arabian Sea.

KEY CONCEPTS

1. A river drain is a specific area, which is known as the catchment area of that river.

2. An area drained by a river and its tributaries is known as a drainage basin.

3. The boundary line separating one drainage basin from the other is called watershed area.

MAJOR DRAINAGE PATTERNS

The drainage patterns are divided into the following ten types:

1. Trellised Drainage Pattern

2. Dendritic Drainage Pattern

3. Rectangular Drainage Pattern

4. Radial Drainage Pattern

5. Centripetal Drainage Pattern

6. Annular Drainage Pattern

7. Barbed Drainage Pattern

8. Pinnate Drainage Pattern

9. Herringbone Drainage Pattern

10. Parallel Drainage Pattern

DENDRITIC DRAINAGE PATTERN

A drainage pattern which looks like tree branches is known as Dendritic drainage pattern. For example, the rivers of northern plain. Dendritic drainage systems (from Greek dendrites, meaning - "of or parallel to a tree") are not straight and are the most common form of drainage system. In a dendritic system, there are many contributing streams (analogous to the twigs of a tree), which are then joined together into the tributaries of the main river (the branches and the trunk of the tree, respectively). They develop where the river channel follows the slope of the terrain. Dendritic systems form in V-shaped valleys; as a result, the rock types must be impervious and non-porous.

RADIAL DRAINAGE PATTERN

Radial drainage patterns form when rivers originate from a hill and flow in all directions. In a radial drainage system, the streams radiate outwards from a central high point. Volcanoes usually display excellent radial drainage. They can sometimes also be found on tops of mountains. Other geological features on which radial drainage commonly develops are domes and laccoliths. On these features the drainage may exhibit a combination of radial patterns. The radical pattern develops when streams flow in different directions from a central peak or dome like structure. In India the Amarkantak range shows the best example of radial drainage pattern.

CENTRIPETAL DRAINAGE PATTERN

Centripetal drainage pattern is formed when rivers discharge their waters from all directions into a lake or a depression. For example, Loktaklake in Manipur. Centripetal or inland drainage pattern (fig. 17.11) is opposite to the radial drainage pattern because it is characterized by the streams which converge at a point which is generally a depression or a basin. This pattern is formed by a series of streams which after emerging from surrounding uplands converge in a central low land which may be a depression, or a basin or a crater lake. The Kathmandu valley of Nepal presents an ideal example of centripetal drainage pattern wherein the tributary streams of the Baghmati converge in the tectonically formed circular basin. The depression formed at the top of Raigarh Dome in the Lower Chambal Basin has given birth to centripetal drainage pattern.

TRELLIS DRAINAGE PATTERN

Trellis drainage pattern is formed when the primary tributaries of main rivers flow parallel to each other and secondary tributaries join them at right angles. For example, rivers in the upper part of the Himalayan region. Trellis drainage is characteristic of folded mountains, such as the Appalachian Mountains in North America and in the north part of Trinidad.

RECTANGULAR DRAINAGE PATTERN

Rectangular pattern is generally developed in the regions where the rock joints form rectangular pattern. The rocks are weathered and eroded along the interfaces of joints, fractures and faults and thus sur­face runoff collects in such long and narrow clefts (resulting from the weathering and erosion of joints) and forms numerous small rills.

These rills are further ex­tended in length and width and become channels. With the march of time a network of streams is developed wherein streams follow the lines of weakness (joints and fractures). The tributaries join their master streams al­most at right angles and thus a rectangular drainage pattern is formed

PARALLEL DRAINAGE PATTERN

Parallel drainage pattern comprises numerous rivers which are parallel to each other and follow the regional slope. This pattern is more frequently devel­oped on newly emerged coastal plains.

The west­ern coastal plains of India represent several examples of parallel drainage patterns where the streams after taking their sources from the western flanks of the Western Ghats drain in straight courses towards west to empty into the Arabian Sea. Parallel drainage pat­tern has also developed on the Eastern Coastal Plains of India. It may be pointed out that a sub-parallel pattern is, therefore, essentially an ‘initial drainage pattern’.

HERRINGBONE DRAINAGE PATTERN

Herringbone drainage pattern, also known as rib pattern, is developed in mountainous areas. The longitudinal consequent streams, as master streams, are developed in the longitudinal parallel valleys while tributaries, as lateral consequents, after originating from the hillslopes of the bordering paral­lel ridges join the longitudinal consequents almost at right angle. The term herringbone has been derived from the pattern of bones of herring fish (mainly spine bones).

PINNATE DRAINAGE PATTERN

The drainage network of the upper Son and Narmada rivers denotes the example of pinnate drainage pattern. This pattern resembles the veins of a leaf.

BARBED DRAINAGE PATTERN

Barbed drainage pattern, a rare kind of drainage pattern, is formed when the tributaries flow in opposite direction to their master streams. The tributaries join their master streams in a hook-shaped bend. Such pattern is generally developed due to river capture. Stream capture, river capture, river piracy or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighbouring stream.

ANNULAR DRAINAGE PATTERN

Annular pattern, also known as ‘circular pat­tern’ is formed when the tributaries of the master consequent streams are developed in the form of a circle. Such pattern is developed over a mature and dissected dome mountain characterised by a series of alternate bands of hard and soft rock beds.

CONCLUSION

Since the project deals with the drainage patterns, it is inherent to underline the risks and challenges associated with river drainage. Experts agree that the best approach to conserving the world's freshwater resources is through managing river basins sustainably. This means making wise choices about resource use, based on an understanding of how to maintain dynamic, living systems in the long term. River basins are important from hydrological, economic and ecological points of view. They absorb and channel the run-off from snow-melt and rainfall which, when wisely managed, can provide fresh drinking water as well as access to food, hydropower, building materials (e.g. reeds for thatching), medicines and recreational opportunities. Hence, efforts should be made to properly and sustainably maintain river drainage basins around the world.