Water logging: causes, effects, remedies

Water logging is the condition in which the water table rises so close to the ground surface that the root zone of crops is saturated: the soil pores are filled with water, so air cannot enter. A field is generally said to be waterlogged when the water table is within about 1.5 m of the ground surface, so that the capillary fringe reaches the root zone.

Causes

1. Seepage from unlined canals and distributaries, which recharges the groundwater continuously.
2. Over-irrigation and wasteful application of water by farmers, causing deep percolation beyond the crop need.
3. Inadequate natural drainage: flat topography, as in the Terai, with no outlet for excess water.
4. Obstruction of natural drains by canals, roads, railways and embankments built across the drainage lines.
5. Heavy rainfall and flooding over an impervious or clayey subsoil.
6. Impervious layer at a shallow depth, which holds the percolated water.
7. Absence or poor maintenance of drains, and lack of canal lining.
8. Rise of the water level in rivers/reservoirs, which raises the groundwater in the adjacent land.

Effects

• Crop yield falls: roots lack oxygen, and nutrient uptake and the activity of soil bacteria are reduced; crops may die.
• Salinity and alkalinity: capillary rise brings salts to the surface, leaving white salt crusts after evaporation.
• Soil temperature falls and tillage becomes difficult; machines cannot work on wet soil.
• Reduced cultivable area and delayed sowing.
• Health problems: mosquitoes and water-borne diseases.
• Damage to the foundations of buildings and roads; loss of land value.

Preventive and remedial (reclamation) measures

Of these, prevention (canal lining, disciplined water use) is cheaper than cure. Where the water table has already risen, a combination of surface drains with tile drains or tube wells is used for reclamation.