PhD

A study on ‘Ground water resources flow modelling and mapping of a
watershed using MODFLOW’, was carried out for Kadalundi river basin of
Malappuram District in Kerala. The objectives of the research were 1. to study the
aquifer characteristics of the study area, 2. to study the spatial and temporal
ground water variations in the study area, 3. to identify the potential ground water
zones within the study area using earth resistivity studies and 4. to develop a
ground water flow model for the river basin using Visual MODFLOW.
Kadalundi river basin has a drainage area of 1122 km 2 with a main stream
length of 130 km, originating from the Western Ghats at the western boundary of
Silent Valley. River flows through the district of Malappuram and downstream
reach of the river falls into Arabian Sea. In order to evaluate the aquifer
characteristics of the study area, spatial and temporal variations of ground water
level of dug wells and bores wells were analyzed separately. Monthly water table
data from 16 bore wells and 14 dug wells during the period from 2008 to 2013
were used for the study. From the p re and post monsoon water table and
piezometric water level variations and from the water table and piezometric water
level hydrograph studies, it was observed that the water table and piezometric
level fluctuation in low land, mid land and high land area were correlated with
rainfall except at some locations like Kottakkal, Marakkara and Tanur.
Hydraulic continuity studies were carried out with the help of statistical
analysis and it indicated that the hydraulic continuity of ground water and surface
water exists between aquifers of dug wells and bore wells in major part of study
area. Areas like Thirurangadi, Kottakkal and Some part of Perinthalmanna,
variation of piezometric water level was poorly correlated with rainfall, which
indicated that hydraulic continuity does not exist in that areas and these areas are
suitable for deep bore wells.Vertical Electrical Sounding (VES) method was carried out using Signal
Stacking Resistivity Meter (MODEL-SSR-MP-ATS) at 22 locations. The
apparent resistivity values obtained from the resistivity meter were interpreted
with the help of ‘IPI2WIN’ software to obtain the layer parameters. The sounding
curves are of A,H,K,Q,HK and KH types reulting in 3 to 4 layer sequence. The
curves are prominently of H, Q, K and A type indicating the presence of three
layer and combination of curves like HK and KH indicating the four sub surface
layers. Most parts of the study area are dominated by H type curve which
indicates the presence of good quantity groundwater.
Visual MODFLOW software version 2.8.1 developed by Waterloo
Hydrogeologic Inc. was used for the flow modelling of the study area. The
conceptual model for the study area was developed based on the base map of
Kadalundi river basin, topo sheet of the area, well logs at 30 sites and the data
obtained from the geophysical studies conducted in the study area. Discretization
was done by dividing it into 62 rows and 136 columns with a grid spacing of 500
m x 500 m throughout the area and the cells outside the boundary of the study
area were made as inactive.
Monthly pumping rate from 35 pumping wells and monthly water level data
from thirty head observation wells of
Ground Water Department (GWD),
Government of Kerala were used as well inputs of Visual MODFLOW.
Hydrogeological parameters such as hydraulic conductivity, specific storage,
specific yield, porosity and initial heads and boundary conditions of the model
domain including constant head, rivers, drains, recharge and evapotranspiration
were used as input of Visual MODFLOW. After uploading input parameters, the
model was run for steady state and transient state subsequently. Model was
developed and calibrated using four years data from 2008 to 2011 and a
reasonably good agreement was obtained between computed and observed water
levels. After calibration, the model was validated for t w o years data of 2012
and 2013. The root mean square error (RMSE) for almost all the wells during
validation were reasonably low and within acceptable limits except a few wellsvery close to the river which are most likely to be influenced by the interflow of
river.
After the model development and validation, it was used to predict the
flow head for
the next 15 years assuming five per cent yearly decrease in
recharge and also to predict the ground water condition by increasing the pumping
rate by 10, 25 and 50 per cent of pumping rate of the validation period (2013).
From the modelling studies, it can be concluded that the Kadalundi river basin
will remain safe for next five years from the point of
future ground water
development and subsequently the water table may reach the bed rock. This
necessitates artificial ground water recharge techniques to supplement the
recharge of rainfall to the ground water.