GS1 PYQ 2018 (Mains Answer Writing): Ground Water Resources | Geography for UPSC CSE PDF Download

“The ideal solution of depleting ground water resources in India is water harvesting system.” How can it be made effective in urban areas?  (UPSC GS1 Mains)

Excess extraction of groundwater is to blame for the 61% decline in groundwater level in wells in India between 2007 and 2017; according to the Central Ground Water Board (CGWB) .Urban centres in India are specifically facing an ironical situation today. On one hand there is the acute water scarcity and on the other, the streets are often flooded during the monsoons. This has led to serious problems with quality and quantityof groundwater. Because of short duration of heavy rain, most of the rain falling on the surface tends to flow away rapidly leaving very little for recharge of groundwater. Most of the traditional water harvesting systems in cities have been neglected and fallen into disuse, worsening the urban water scenario. One of the solutions to the urban water crisis is rainwater harvesting - capturing the runoff.
Water harvesting as solution to depleting ground water resources in India: 

• Rain water available from rooftop of building, paved and unpaved areas needs to be harvested. 
• Water spreading: Means diverting or collecting runoff from natural channels, gullies, or streams with a system of dams, dikes, ditches, or other means, and spreading it over a relatively flat area. 
• Rooftop collection of rainwater: Rooftop Rain Water Harvesting is the technique through which rain water is captured from the roof catchments and stored in reservoirs. Harvested rain water can be stored in sub-surface ground water reservoir by adopting artificial recharge techniques to meet the household needs through storage in tanks. 
• Applying the Sponge City concept: It indicates a particular type of city that does not act like an impermeable system not allowing any water to filter through the ground, but, more like a sponge actually absorbs the rain water, which is then naturally filtered by the soil and allowed to reach into the urban aquifers. This allows for the extraction of water from the ground through urban or peri-urban wells. This water can be easily treated and used for the city water supply. 
• Recharge pit: In alluvial areas where permeable rocks are exposed on the land surface or are located at very shallow depth, rain water harvesting can be done through recharge pits. The technique is suitable for buildings having a roof area of 100 sq.m. These are constructed for recharging the shallow aquifers. 
• Recharge trench: Recharge trenches are suitable for buildings having roof area of 200-300 sq. m. and where permeable strata are available at shallow depths. 
• Tube wells: In areas where the shallow aquifers have dried up and existing tubewells are tapping deeper aquifer, rain water harvesting through existing tubewell can be adopted to recharge the deeper aquifer 
• Trench with recharge well: In areas where the surface soil is impervious and large quantities of roof water or surface runoff is available within a very short period of heavy rainfall, the use of trench/ pits is made to store the water in a filter media and subsequently recharge to ground water through specially constructed recharge wells. This technique is ideally suited for area where permeable horizon is within 3m below ground level. 
• Ground water exploitation is inevitable is Urban areas. But the groundwater potential is getting reduced due to urbanisation resulting in over exploitation. Hence, a strategy to implement the groundwater recharge, in a major way need to be launched with concerted efforts by various Governmental and Non-Governmental Agencies and Public at large to build up the water table and make the groundwater resource, a reliable and sustainable source for supplementing water supply needs of the urban dwellers.

Topics covered - Groundwater in India, Water system in India