Groundwater Flow and Transport Modelling Around Gurupura Wetlands, Karnataka, India

The water demand in the world is rapidly increasing due to population growth, extensive industrialization and agricultural practices. Groundwater plays an important role in the supplying of this ever increasing water demand. Therefore, accurate estimation of groundwater resources is a prerequisite for any sustainable water management especially in water scarce (semi-arid) areas. India has been blessed with a vast stretch of coastline. Many urban centres of the country are located on the coastal tract apart from thousands of villages and industrial settlements. Water resources in these coastal areas and wetlands take up a special significance since any developmental activity will largely depend upon availability of fresh water to meet domestic, industrial and agricultural requirements. Groundwater withdrawals in excess of safe yields and reduced recharges to groundwater due to rapidly changing land use pattern along the coasts have increased the incidences of seawater intrusions into the coastal aquifers. Groundwater modelling is an essential tool in the groundwater system in response to future stresses due to abstractions and land cover changes. Numerical groundwater flow models solve the distribution of hydraulic head and describe flow whereas numerical transport models solve the distribution of solute concentration due to advection, dispersion and chemical reactions. In the present study an attempt is made to formulate groundwater flow and transport modelling in and around wetlands of Gurupura basin in Karnataka state of India. The study intended to simulate the response of an unconfined, shallow, tropical coastal aquifer comprising of wetlands using SEAWAT. The numerical simulation of groundwater flow was carried out by building a MODFLOW model of the basin and the transport parameters are assigned to execute the MT3DMS model. Finally, the SEAWAT model which is a coupled version of MODFLOW and MT3DMS designed to simulate three dimensional, variability density groundwater flow and multi-species transport, is developed. The model is calibrated from August 2011 to August 2013 using observed groundwater heads and TDS data obtained from 27 observation wells. The data from VES (Vertical Electrical Sounding) and pumping tests conducted in the study area are used for aquifer characterization. The model is validated for 2013-2015. The model performance is encouraging except for monsoon months (June to September), while evaluating with three techniques R², RMSE and NSE. Overall the model performance is satisfactory with NSE≥0.5.The spatial distribution of simulated groundwater map shows presence of groundwater at a higher level in the areas around wetlands in the study area, even during peak summer months (April and May). The sensitivity analysis conducted shows that the aquifer is sensitive to specific yield, hydraulic conductivity and recharge rate. The simulation of solute transport model reveals the presence of TDS concentrations in and around the wetland regions during winter and summer seasons, but within safe range. The groundwater budget was estimated for the aquifer using groundwater mass balance simulation package ‘ZONEBUDGET’. This analysis shows that during the period of maximum potential position (August), the component of groundwater contributing to wetland is 4.5% of total budget. During dry season with minimum potential head, the groundwater contribution to wetland is 1.4%. Hence, the presence of water in the wetland during the non-monsoon months is established by the contribution of only groundwater, in the study area.