Groundwater, the lifeline of India
Over 55 percent of India’s population relies on groundwater for irrigation, water for cattle, domestic consumption, and industrial use making India the world’s greatest groundwater extractor, surpassing the USA and China combined.
This paper titled 'Assessment of traditional rainwater harvesting system in barren lands of a semi-arid region: A case study of Rajasthan (India)' published in the Journal of Hydrology, Regional Studies informs that as high as 16 percent of the aquifers in India are overexploited and an additional 3 percent are in a critical state. The declines in water levels are severe with rates of 1–2 m year-1 since 2000. These have not only affected small-scale farming, but also led to deterioration of groundwater quality in many locations.
Managed Aquifer Recharge (MAR), or Artificial Recharge, has emerged as a solution to deal with this situation since the 1960s that has been supported by governmental and civil institutions and included in the central government policies on groundwater management since the 1990s. While rainwater harvesting is not new to India, MAR takes it further by helping to store a portion of the vast runoff volume generated during the monsoon by increasing its standing time and allowing it to percolate into depleted aquifers.
The latest Master Plan for Artificial Recharge to Ground Water by the CGWB (2013) proposes the need for 11 million recharge structures with a recharge capacity of 85.5 billion cubic meters per year to deal with the 34 percent groundwater deficit due to overextraction in India.
Chaukas of Rajasthan
Many structures are used for rainwater harvesting in arid to semi-arid environments and one such example of localised solutions to catch the rainfall includes shallow infiltration ponds, namely Chaukas of Rajasthan - a system developed by a local community organisation, Gram Vikas Navuyak Mandal Lapodiya (GVNML).
The size of locally managed aquifer recharge structures is small with limited water holding capacity and their contribution to the groundwater recharge is not much. Thus they may not be very reliable on their own during drought years and may not provide additional benefits in catchments with other larger MAR structures.
However, these small structures can redistribute the harvested rainwater in the catchment by converting the excess runoff into recharge by controlling the effect of variables like evaporation, soil moisture and streamflow in the total water balance.
While various rainwater harvesting methods have been studied to understand their hydrological impacts on the surrounding aquifers, no studies exist that have looked at the recharge potential of the Chaukas. This study aimed at quantifying the recharge potential of Chaukas in barren lands of Lapodiya region in Rajasthan and their impact on vegetation cover.
Most of Rajasthan is barren and lacks vegetation coverage and has sandy, loamy, saline, alkaline, and chalky (calcareous) soil. Groundwater is the major (91 percent) source of water for drinking and 66 percent of the aquifers in Rajasthan are overexploited.
Water shortages are common including that in the Lapodiya catchment and various rainwater harvesting structures such as farm ponds, Talabs (ponds), Chauka system, Nadis (small ponds), and Anicuts (check dams) have been installed to harness rainwater in the catchment.
Rural villages in the region mainly practise agriculture and animal husbandry, which is facing challenges as uncontrolled grazing has denuded the land in the area of perennial grass cover. Gram Vikas Navuyak Mandal Lapodiya (GVNML) has implemented a Chauka and Nadi system to take on water quantity and quality problems.
What is the Chauka system
"The Chauka forms an enclosure about 2000 m2 , built across a gently sloping area by placing earthen dykes on the sides. One Chauka trench can contain up to 25–30 cm of water when it is filled are infiltration ponds developed locally to support pastoral lands in the early dry season. They are designed to hold little runoff water that slowly infiltrates in the soil and are built-in series so that when one Chauka gets filled, it will overflow to the adjoining Chaukas. The excess water from the Chaukas flows to the nearby Nadi or Talab"(pp 4) .
During the monsoon season, the excess rainwater from Chauka and ponds flows into the river. This seasonal river meets a larger dam downstream that provides water to many districts in Rajasthan. This network of ponds, check dams, and Chauka systems harness the rainwater during the monsoon season for future use. At the same time, they maintain the soil moisture at a satisfactory level for pasture growth.
While rainwater harvesting using these traditional and modern structures has been considered very useful in developing pasturelands and enhancing groundwater recharge, this has not been supported by evidence in the region. The Lapodiya catchment was identified for conducting detailed studies of the Chauka system from 2019 to 2020.
The study found that:
- In the monsoon season of 2019 and 2020, the Chauka system’s additional storage provided more water for potential groundwater recharge. The average daily water table rise in 2020 was higher (29 mm/day) than in 2019, as the larger number of rainy days permitted more recharge, even though the total rainfall was less in 2020. The rise in water levels in the wells indicated this cumulative potential recharge in both the 2019 and 2020 monsoon seasons.
- The Chauka system helped an additional 5.1 percent and 4.9 percent of the total rainfall to recharge groundwater during the monsoon season of 2019 and 2020, respectively. The ability of Chauka systems to intercept runoff and provide additional recharge was reflected in the increase in recharge from 19 percent in 2019 to 46 percent in 2020. This high interception of runoff is extremely important for this region which has significant variability in the rainfall both at spatial and temporal scales.
- The groundwater recharge in the area depended on rainfall patterns, which determined the rate and pattern of the water balance components and the groundwater resources.
- The study revealed that an additional 5 percent of the rainfall depth was being recharged into the groundwater.
- Increase in soil moisture also helped natural grass cover to develop, which could be used by the local community as pastureland.
"The Chauka system can provide a sustainable alternative to manage water resources in water stressed regions and livelihood support through development of pastures for animal husbandry. These advantages highlight their potential to be scaled up and replicated in other water stressed parts of India or the world that have barren land that is slightly sloping, together with permeable soils, which are the only necessary conditions needed for the construction of Chaukas" concludes the study.
The full paper can be accessed here
/articles/greening-barren-lands-local-way