Waterlogging

Topic: Soils of India: Types, Degradation and Conservation · NCERT: Class 10, Ch 1 "Resources and Development"; Class 12, Ch 3 "Land Resources and Agriculture"; Class 12, Ch 6 "Planning and Sustainable Development in Indian Context"; Class 12, Ch 9 "Geographical Perspective on Selected Issues and Problems"

Meaning

Waterlogging happens when the water table (the top level of the groundwater) rises into the root zone (the top layer of soil where plant roots grow), so the soil around the roots stays soaked with water. It matters because crops in such soil become weak or die. It is also the first step towards salty and alkaline land, which has become a major hidden cost of canal irrigation in north-west India.

Explanation

How it forms: cause → process → result

• Cause 1, over-irrigation:
• Farmers give their fields more water than the crops need.

• The extra water sinks down and adds to the groundwater.

• Cause 2, seepage from unlined canals:

• In an unlined canal, the bed and sides are bare earth, not concrete or brick.

• Water leaks out of the canal and raises the water table on both sides of it.

• Process: water is added from above year after year. If it cannot drain away, the water table keeps rising.

• Result: the water table reaches the roots. The soil pores fill with water, the roots cannot get air, and crop yields fall.

Conditions that make it worse

• Poor natural drainage:
• In flat land, water does not run off.

• Heavy black and alluvial soils drain slowly, so irrigation water collects in them.

• Hard layers under the soil:

• In parts of the Thar Desert, the sandy soil sits on hard layers.

• Water cannot sink past these layers, so it builds up near the surface.

• Heavy irrigation in a water-hungry cropping system: the rice–wheat system of the Punjab–Haryana plains uses large amounts of canal and tube-well water.

The next stage: salinisation and alkalisation

• Salinisation means salts build up in the topsoil. Alkalisation means sodium carbonate builds up, the soil's pH goes up, and the soil turns alkaline. Such soil is also called sodic soil.

• Step by step: 1. Waterlogging brings the water table close to the surface. 2. Capillary action pulls groundwater up through tiny pores in the soil, the way oil climbs up a lamp wick. 3. In the hot, dry climate of north-west India, this water evaporates from the surface. 4. The salts dissolved in the water stay behind and form a white crust. 5. If the salt is mostly sodium carbonate, the soil also becomes alkaline. It turns hard and sticky, and water cannot pass through it.

• Local names for these salty, barren soils are reh, kallar and usar.

Remedies

• Canal lining: the canal bed and sides are covered with concrete or brick, so less water leaks out.
• Drip irrigation: water is given drop by drop at the roots. Little extra water sinks into the ground.
• Sub-surface drainage (SSD): perforated pipes (pipes with small holes) are laid underground. They collect the extra salty water and carry it away from the field.
• In waterlogged and saline areas of Haryana, SSD brought fallow land (land left unused) back under farming. Crop yields and farm incomes went up, and farmers moved to more profitable crops [2].

• SSD works only when there is a safe way to get rid of the salty drainage water and enough fresh water to wash the salts out of the soil [2].

• Gypsum (calcium sulphate): the calcium in gypsum takes the place of sodium on the soil particles. Irrigation water then washes the freed sodium below the root zone. This is the main way to reclaim alkaline (usar) soils.

• Salt-tolerant crop varieties: crops bred to grow even in somewhat salty soil.

Where it occurs

• Punjab, Haryana and western Uttar Pradesh: over-irrigation is the main cause of land degradation here. It leads to waterlogging and then to salinity and alkalinity.
• Indira Gandhi Canal command area, western Rajasthan (Thar Desert):
• A command area is the land that a canal or dam project can irrigate.
• The canal starts at the Harike Barrage in Punjab, where the Sutlej and Beas rivers meet, and carries water deep into the desert.

• The desert soil sits on hard layers, so the extra water cannot drain away and the water table rises.

• Punjab–Haryana plains (north-west alluvial plain): heavy canal and tube-well irrigation for the rice–wheat cropping system. Alluvial soil is soil laid down by rivers.

• Sharda Sahayak command, central and eastern Uttar Pradesh: the canal system takes water from the Sharda river. Canal seepage and flat, poorly drained land raise the water table.
• Chambal command, the Kota region of Rajasthan and the Chambal area of Madhya Pradesh: heavy black and alluvial soils drain slowly, so irrigation water collects in them.
• Elsewhere in the world: the same canal-irrigation problem is seen in the Indus basin of Pakistan and the Aral Sea basin of Central Asia.

Don't confuse with

• Salinisation: waterlogging is a water problem, where soaked roots get no air. Salinisation is a salt problem: salts build up in the topsoil after capillary rise and evaporation. Waterlogging usually comes first.
• Alkalisation (sodic soil): this is caused by sodium carbonate and raises soil pH. It is fixed with gypsum. Waterlogging is fixed by draining water away, through canal lining, drip irrigation and sub-surface drainage.
• Flooding: a flood is surface water that covers the land for a short time. Waterlogging comes from below, when the groundwater table rises into the root zone, and it can last for years.
• Desertification: this is land degradation in drylands (arid, semi-arid and dry sub-humid areas). Waterlogging is the opposite problem, too much water, but it can happen inside a desert, as in the Indira Gandhi Canal command.

Prelims Hooks

• Over-irrigation, not mining or overgrazing, is the main cause of land degradation in Punjab. It is also the main cause in Haryana and western Uttar Pradesh.
• Order of processes: waterlogging → capillary rise → evaporation → salinisation.
• Sodium carbonate causes alkalisation. Gypsum is the remedy for alkaline (usar) soil.
• Indira Gandhi Canal: it starts at the Harike Barrage (Sutlej–Beas confluence, Punjab) and waterlogs parts of western Rajasthan.
• Local names for salty or alkaline barren soils are reh, kallar and usar.
• Command–state matches: Sharda Sahayak is in Uttar Pradesh. Chambal command covers Kota (Rajasthan) and the Chambal area of Madhya Pradesh. The Indira Gandhi Canal command is in western Rajasthan.

Mains Points

• A cost of the Green Revolution (GS-III):
• Free or cheap power and water, unlined canals and the rice–wheat cropping system in Punjab–Haryana made the water table rise.

• This led to waterlogging, then to salinity and alkalinity, and productive land became barren reh and kallar land.

• A package of remedies:

• Canal lining and drip or sprinkler irrigation cut the extra water going into the ground.
• Sub-surface drainage brought land back into farming in Haryana and raised farm incomes [2]. It needs a safe way to dispose of the salty drainage water [2].

• Gypsum reclaims alkaline soils. Crop diversification and water-pricing reform address the root cause.

• Regional lesson: irrigation-induced degradation is concentrated in the north-west plains and in canal command areas such as the Indira Gandhi, Sharda Sahayak and Chambal commands. Here the answer is water management. Mining areas need mine reclamation, and dry overgrazed states need grazing control. The same problem in the Indus and Aral Sea basins shows that it is a global risk of large canal projects.

Related concepts

• Soil degradation
• Soil salinisation and alkalisation
• UN Convention to Combat Desertification

Read more

• Land degradation: waterlogging, salinity and desertification