EFFECT OF BAKKIKAYAM REGULATOR ON GROUNDWATER USING GEOPHYSICAL TECHNIQUES AND VISUAL MODFLOW

Abstract

A study on ‘Effect of Bakkikayam Regulator on groundwater using Geophysical Techniques and Visual MODFLOW’ was conducted at the ayacut areas of Bakkikayam regulaor, situated across the Kadalundi River at Pandikasala, Vengara, Malappuram district. The objectives of the research work were to study the aquifer characteristics of the area using earth resistivity studies, to assess the groundwater flow variation due to the presence of Bakkikayam Regulator, to develop ground water resource map of the study area using Visual MODFLOW and to identify the potential ground water zones of the study area. In order to analyze the aquifer characteristics of the study area, Vertical Electrical Sounding (VES) survey was carried out using Signal Stacking Resistivity Meter (MODEL-SSR-MP-ATS at 18 locations and were interpreted using IPI2WIN software. The sounding curve obtained from the interpretation of resistivity studies revealed that most part of the study area showed H and HK type curve indicating the presence of good to moderate quality ground water. From the VES studies it could be concluded that, top soil of the study area is either laterite soil or hydromorphic soil of thickness 0.75 to 4 m, followed by laterites with varying hardness to a depth of 4 m to 17 m. Lithomargic clay of thickness less than 2 m is seen below the laterites in some places. These layers are overlying weathered rock of 2 to 14 m thickness followed by hard rock with or without fractures. Major aquifer formations in the study area are identified as laterite, clay and weathered rock. Effect of bakkikayam regulator on ground water variation was analyzed based on pre and post monsoon water table data. The ground water level during pre and post monsoon from dug wells located in upstream and downstream side of the Bakkikayam regulator were observed and the difference between pre and post monsoon water table (water table fluctuations) were noted .It was observed that the water table fluctuation in the wells located in downstream side ranged from 5.41 to 5.62 m.Visual MODFLOW software version 2.8.1 was used for the groundwater modeling of the study area. A base map was prepared and imported in to the model as bmp format. The conceptual model for the study area was developed using base map, well logs and the data collected by conducting geophysical survey of the study area and the study area was discretized by dividing into 50 rows and 50 columns with a grid spacing of 530 m x 520 m. By comparing the water table contour map obtained from the validated model before and after the implementation of Bakkikayam Regulator, it could be seen that the light blue color is changed to green color, indicating that there was a decline of 3 to 4 m water table in the downstream side of the regulator. The validated model was used to predict the water table contour map of the study area for the next five years by increasing the recharge rate 10, 20 and 30 percent of the recharge rate of the validated period (2019). An increase in water table of 2m was observed during the predicted period due to 20% increase of ground water recharge rate. Beyond that there was no significant change in water table and remained more or less constant. This is due to the reason that topography of the downstream area of the Bakkikayam regulator especially parts of Nannambra and Tirurangadi Panchayaths comes under low land. The ground water flow from this area is towards the river and from where water drains into Arabian Sea. This necessitates some obstructions to check the flow of river or any other water conservation measures at downstream side. From the velocity vector map obtained using the Visual MODFLOW model, it was observed that the flow direction and magnitude were maximum in two water bodies locally named ‘Morya Kappu’ and ‘Venchali Kappu’, which can be identified as high ground water potential area. At present these water bodies and their drainage channels of around 10,000 m are filled with sediment deposits. Hence it is recommended that the deepening of two water bodies upto 3 m and their drainage channels upto 1.6 m, is essential to solve the problems encountered for paddy cultivation in Nannambra Panchayath to a large extent.