Groundwater Flow Modelling Using Visual MODFLOW Flex- A Case Study of
Thuthapuzha sub-basin, Kerala, India
India is the largest user of groundwater in the world, accounting for a
quarter of the world’s annual groundwater extraction. In Kerala, a state
in Southern India, groundwater is the drinking water source for 62% of
the population. Groundwater management is vital to ensure the
sustainable availability of water. However, it is complex due to
uncertainties in subsurface parameters. Groundwater modeling can be used
as an efficient tool to understand the regional flow as well as the
hydrogeological condition of the groundwater system. The modular
finite-difference groundwater flow model (MODFLOW) developed by the U.S.
Geological Survey (USGS) is a widely used modular three-dimensional
block-centered finite difference code used for simulating dynamic
features and scenarios in groundwater systems. In this study, the Visual
MODFLOW Flex 7.0 is used to simulate the flow of groundwater through
aquifers in the Thuthapuzha sub-basin, a sixth-order sub-basin of the
Bharathapuzha river basin Kerala’s second-largest river basin. A
four-layer model covering an area of 940 km2 has been
prepared using Visual MODFLOW Flex 7.0. Groundwater level data of 37
wells spread over the study area has been used for the model simulation.
Model design, calibration, and validation have been carried out.
Boundary conditions including recharge and evapotranspiration are
derived from the Soil and Water Assessment Tool (SWAT) hydrologic model.
The model calibration is performed in two stages, which include
steady-state calibration and transient state calibration using observed
groundwater levels from 2000 - 2016. The validation is done by using
observed groundwater levels from 2017 - 2019. The spatial distribution
of hydraulic conductivity and storage properties are optimized using a
combination of the trial-and-error method. Model performance evaluation
is done using Standard Error of the Estimate, Root Mean Squared and
Normalized RMS, found to be in the optimum range. The results of the
model are found in good agreement with the observed groundwater level
data. Therefore, the model is suitable for studying the groundwater
level changes in the study area. In addition, the model can be extended
to study the groundwater flow dynamics of the whole Bharathapuzha river
basin and similar subbasins for the sustainable planning and management
of groundwater resources.