Centripetal drainage pattern

Topic: Drainage System of India: Rivers, Basins and Patterns · NCERT: Class 11, Ch 3 "Drainage System"

Meaning

A centripetal drainage pattern is a pattern in which streams flow inward from all sides into a central lake or depression (a low-lying hollow in the land). It is the opposite of radial drainage. It matters because the shape of the streams shows the shape of the land. Such basins are also fragile: silt and pollutants have no way out, so they collect in the central lake.

Explanation

How it forms

• The land slopes inward
• The land slopes down toward one central low point.
• Rain falling on any side runs downhill toward that centre.

• So all the water collects in the middle.

• Streams meet at a single point

• The streams come together at a single outlet or sink (a low spot where water gathers and has no easy way out) [3].

• On a map, the streams look like the spokes of a wheel pointing inward.

• Result: a lake, swamp or salt pan forms at the centre. Examples are Loktak Lake (freshwater) and Sambhar Lake (salt water).

Conditions it needs

• A basin-shaped surface: high land on the edges and low land in the middle.
• No easy outlet: the central low point keeps the water. It does not pass the water on to a bigger river.
• Typical settings around the world [3]:
• Craters: bowl-shaped hollows, for example at the top of an old volcano.
• Eroded domes with weak cores: the soft rock in the centre of a dome wears away faster than the edges, which leaves a hollow.
• Limestone country: rock that dissolves in water and forms sinks.
• Enclosed desert depressions: low basins in dry lands with no river flowing out.

What happens in the central basin

• Everything flows to the centre
• Silt (fine soil carried by water), nutrients and pollutants all flow to the lake.

• With no outlet, they settle there and build up.

• In dry climates the lake turns salty

• Water evaporates from the lake, but the salts stay behind.
• This is why Sambhar is a saline (salt) lake.

Where it occurs

• India: Loktak Lake, Manipur
• It is a large freshwater lake with swamps, fed by several streams [4].
• It was named a Ramsar site on 23 March 1990 and covers 26,600 ha [4]. (A Ramsar site is a wetland of international importance under the Ramsar Convention of 1971.)
• Its special feature is the phumdis: thick, floating mats of weeds covered with soil [4].

• It was put on the Montreux Record in 1993 because of catchment deforestation, water hyacinth and pollution [4]. (The Montreux Record is the Ramsar list of sites whose ecology is under threat.)

• India: Sambhar Lake basin, Rajasthan

• It is a large saline lake fed by four streams, a clear case of inward drainage [5].
• It was named a Ramsar site on 23 March 1990 and covers 24,000 ha [5].

• It is an important site for the Dalmatian pelican, the greylag goose and the common crane [5].

• World: some craters, eroded domes with weak cores, parts of limestone country and enclosed desert depressions [3].

Don't confuse with

• Radial drainage: the flow goes outward from a high centre, such as the Amarkantak plateau (Narmada to the west, Son to the north, Mahanadi headwaters to the east and south). Centripetal flow goes inward to a low centre (Loktak, Sambhar).
• Annular drainage: the streams curve in rings around an eroded dome [2]. In centripetal drainage, the streams run straight inward to one central sink.
• Deranged drainage: this is a disordered pattern with channels broken up by lakes and swamps. It forms on land from which continental ice has recently melted [2]. It has many scattered lakes, while centripetal drainage has one central lake or depression.
• Dendritic drainage: this is a tree-like pattern in which tributaries join a main river at acute angles on uniform rock, as on the northern plain. The water leaves through the main river. In centripetal drainage, the water ends up in a central basin.

Prelims Hooks

• Centripetal = streams flow inward into a central lake or depression. Radial = streams flow outward from a high centre. This is NCERT Exercise pair 2(iii).
• Indian examples: Loktak Lake (Manipur) and Sambhar Lake (Rajasthan). Amarkantak is radial, not centripetal. It is a common trap.
• Loktak and Sambhar both became Ramsar sites on 23 March 1990. Loktak covers 26,600 ha [4] and Sambhar covers 24,000 ha [5].
• Phumdis (floating mats of weeds and soil) are found in Loktak [4]. Loktak has been on the Montreux Record since 1993 [4].
• Sambhar is a saline lake fed by four streams [5].
• World settings: craters, eroded domes with weak cores, limestone country and enclosed desert depressions [3]. Volcanic cones usually give radial drainage, not centripetal [2].

Mains Points

• Centripetal basins are fragile (GS-III, environment)
• They have no outlet, so silt, nutrients and pollutants collect in the central lake.
• Loktak faces catchment deforestation, water hyacinth and pollution, which is why it is on the Montreux Record [4]. Sambhar is saline and is under pressure from salt mining.

• Answer: protect and manage the whole catchment (all the land that drains into the lake), not only the lake itself.

• Drainage patterns show the landform (GS-I)

• A centripetal pattern on a map tells you there is a closed basin, a crater, an eroded dome or a desert depression underneath.

• This helps in reading topographical sheets and in understanding how the land formed.

• Planning use

• All the water gathers at one point, so floodwater collects in the central lake.
• Planners must allow for this when they choose where to build homes, farms and drainage works around such lakes.

Related concepts

• Drainage pattern
• Dendritic drainage pattern
• Radial drainage pattern
• Trellis drainage pattern
• Amarkantak plateau

Read more

• Drainage patterns