Q.What do you understand by ground water? Describe the causes for its depletion and remedies.

Ground water = subsurface water stored in aquifers. It is being depleted by over-pumping, deforestation, reduced recharge and pollution; remedies are rain-water harvesting, artificial recharge, afforestation and efficient/economical water use.

Ground water:

Ground water is the water that lies beneath the surface of the earth, occupying the pore spaces and cracks of soil, sand and rock. The layer of water-saturated rock that stores and yields this water is called an aquifer, and the upper limit of the saturated zone is the water table. Ground water is our chief source of drinking and irrigation water and is drawn out through wells, tube-wells and hand pumps.

Causes of depletion:

1. Over-extraction: Excessive pumping of ground water for irrigation, industry and drinking (especially by tube-wells) withdraws water faster than it is naturally replenished, so the water table keeps falling.
2. Reduced recharge due to deforestation and urbanisation: Cutting of forests and covering the land with concrete/roads (loss of open, vegetated ground) reduces percolation of rain water into the soil.
3. Increasing population and rapid industrial/agricultural demand.
4. Poor/erratic rainfall and low natural recharge.
5. Pollution of aquifers by sewage, fertilisers, pesticides and industrial effluents, which spoils the usable ground water.

Remedies:

1. Rain-water harvesting: collect and store rain water and let it percolate to recharge the ground water.
2. Artificial recharge of aquifers through recharge pits, check dams and percolation tanks. …

(a) Rainwater harvesting conserves and recharges water to relieve crisis; (b) hydrophytes are grouped by their position relative to the water surface, from free-floating to amphibious.

(a) Solution to Water Crisis: Rainwater Harvesting

One effective solution to the growing water crisis is rainwater harvesting -- the collection and storage of rainwater, either in surface tanks/ponds or by directing it to recharge underground aquifers, instead of allowing it to run off and be lost.

Rainwater harvesting can be practised at the household level (roof-top collection systems directing water to storage tanks or recharge pits) or at a larger community/watershed level (check dams, percolation ponds).

Its advantages include: conservation of a valuable natural resource that would otherwise be lost as runoff; recharging of depleting groundwater tables, ensuring a more reliable water supply for drinking and irrigation; reduced dependence on, and cost of, externally supplied water; reduced urban flooding, since collected rainwater does not overload stormwater drains; and reduced soil erosion, since less water runs uncontrolled over land surfaces. (Other valid solutions include watershed management, drip irrigation to minimise agricultural water wastage, and treated wastewater recycling and reuse.)

(b) Types of Hydrophytes

Hydrophytes are plants specially adapted to grow in or on water, and are classified based on their position relative to the water surface:

1. Free-floating hydrophytes: roots are not attached to the substratum; the plant floats freely on the water surface, e.g., Eichhornia (water hyacinth), Pistia (water lettuce), and Lemna (duckweed).
2. Rooted-floating hydrophytes: rooted in the mud at the bottom, but the leaves float on the water surface, e.g., Nymphaea (water lily) and Nelumbo (lotus). …