Abstract:
Recharge zones and sources in an urban setup
(NCT of Delhi, India) were identified using environmental
isotopes (2H, 3H, 18O); they were then correlated with
hydrogeological conditions. The isotopic results showed
that groundwater is being recharged by surface water
during the dry season, while recharge associated with
local precipitation becomes prominent during the monsoon.
The effect of source-water evaporation and altitude
on the isotopic characteristics of groundwater was clearly
noted. A gradual increase in groundwater age, i.e.
decrease in tritium content, while moving away from the
river/canals/drains, suggests a degree of mixing of oldaged
groundwater with relatively young recharging water.
Further, to substantiate the findings of isotopic investigations,
surface recharge conditions were differentiated
into potential pervious (recharge prone) and impervious
(recharge resistant) surfaces through mapping of potential
recharge areas based on soil type and water-table depth, to
depict a three-dimensional illustration of hydrogeologically
mediated recharge zones of the area. The hydrogeological
evidence thus obtained about the spatial
distribution of permeable zones, slope and boundary
conditions, aptly substantiates the isotopic findings. The
study seeks its impact by correlation of the isotopic
findings with the regional groundwater flow regime which
has been altered by the urban development.
