Abstract:
Groundwater recharge is an important metric
for sustainable water management, particularly in semiarid
regions. Hard-rock aquifers underlie two-thirds of
India and appropriate techniques for estimating groundwater
recharge are needed, but the accuracy of such values
is highly uncertain. The chloride mass balance (CMB)
method was employed to estimate annual groundwater
recharge rates in a monsoon-dependent area of Jaisamand
Lake basin in Rajasthan, which contains the Gangeshwar
watershed. A monitoring program was established within
the watershed during summer 2009, with local participation
for the collection of rainfall and groundwater
samples. Groundwater recharge was estimated spatially
over a 3-year period with pre-monsoon and post-monsoon
datasets. Recharge rates estimated using the CMB method
were then compared to those estimated using the watertable
fluctuation (WTF) method. Specific yield was
0.63 % and assumed to be homogenous across the
watershed. The average recharge rate derived from the
WTF method (31 mm/year) was higher than that derived
from the CMB method (24.3 mm/year). CMB recharge
rates were also applied to obtain a water balance for the
watershed. CMB recharge rates were used to estimate
annual groundwater replenishment and were compared
with estimates of groundwater withdrawal using Landsat
imagery. Over the 2009–2011 study period, groundwater
demand was about seven times greater than the estimated
groundwater renewal of 5.6 million cubic meters. This
analysis highlights the challenges associated with estimating
groundwater recharge in fractured hard-rock aquifers,
and how renewable groundwater-resource estimates can
be used as a metric to promote sustainable water use.
