Management of Natural Resources

RAINWATER HARVESTING

• It is an age-old practice in India, where rainwater is collected when it falls on the earth, stored and utilized at a later point.
• Water is stored in artificially designed systems like artificially repaired impervious or semi-pervious land surface, natural or man-made catchment areas like rooftops, compounds, rock surface and hill slopes.
• Water harvesting are various process followed in different parts of the country (and world) for conserving water and aimed at its sustainable use.

Factors affecting rainwater harvesting

The various factors affecting rainwater harvesting are:

• Frequency and quantity of rainfall
• Characteristics of catchments
• Demand of water
• Quantum of runoff
• Speed and ease with which rainwater percolates through the subsoil to recharge the groundwater.

ALTERNATE NAMES FOR WATER HARVESTING SYSTEM

There are many names given to the water harvesting system, like:

• Khadins, tanks and nadis in Rajasthan,
• Bandharas and talsin in Maharashtra,
• bundhisin in Madhya Pradesh and Uttar Pradesh,
• aharsand pynes in Bihar,
• kulhs in Himachal Pradesh,
• ponds in the Kandi belt of Jammu region,
• and eris(tanks) in Tamil Nadu,
• surangams in Kerala, and
• katas in Karnataka

WATER HARVESTING SYSTEM

In level terrain, the water harvesting structures are mainly crescent shaped earthen embankments or low, straight concrete and rubble “check dams” built across seasonally flooded gullies. Monsoon rains fill ponds behind the structures. Only the largest structures hold water year round; most dry up six months or less after the monsoons. Their main purpose, however, is not to hold surface water but to recharge the groundwater beneath.

Advantages

The various advantages of water stored in the ground are as follows:

• It utilises natural resources and reduces the need for imported water, flooding, storm water runoff, erosion and contamination of surface water with pesticides, sediment, metals and fertilizers.
• Home systems are relatively simple to install and operate; it could reduce water bill and promote both water and energy conservation.
• It does not require a filtration system for landscape irrigation since no chemicals such as fluoride and chlorine and no dissolved salts and minerals from the soi are involved.
• It does not evaporate.
• It spreads out to recharge wells and provides moisture for crops over a wide area.
• It does not promote breeding of mosquitoes (unlike stagnant water collected in ponds or artificial lakes).
• It is protected from contamination by human and animal wastes.
• It is utilised for the benefit of local population.

Disadvantages of Rainwater Harvesting

• Rainfall is limited and unpredictable.
• The installation, storage and delivery systems may be costly and the return or payback period depends on the size and complexity of the system.
• It requires technical knowhow for installation, else it may attract mosquitoes and other waterborne diseases.
• Chemiocals, pesticides and other pollutants may seep in through certain systems, contaminating water and affecting plants

RAINWATER HARVESTING IN URBAN AREAS (CITY AREAS)

In urban areas (city areas), however, most of the ground is covered with buildings, concrete pavements and metalled roads due to which only very little rainwater seeps into the ground naturally.

The rainwater harvesting from open spaces around the buildings in a city is done by constructing percolation pits covered with concrete slabs having holes in them, and connected to a recharge well through a pipe.