Assessment of saline water intrusion from Ponnani to Tavanur along the course of river Bharathapuzha

Abstract

The study on „Assessment of saline water intrusion from Ponnani to Tavanur along the course of river Bharathapuzha‟ was done with the objectives to prepare the base map and landuse map of the study area, to develop a groundwater flow model, and to understand the saline water intrusion in coastal aquifers of Ponnani region. The study area involves part of Tavanur and Ponnani regions of Bharathapuzha river basin having geographical location of 10.76° to 10.85° North latitude and 75.88° to 76° East longitude, which comprises of about 50 km2 area.For modelling groundwater resources and salt movement, visual MODFLOW is recognized as a useful tool. In this study, Visual MODFLOW 2.8.1 integrated with MT3D software was used for ground water modelling and modelling saline water intrusion.The land use map of the area was prepared in ERDAS Imagine software using supervised classification. The area was divided into 50 columns and 50 rows (2500 cells).Water level and water quality data of observation wells were measured from the field and secondary data obtained from the wells of Central Water Commission in the study area were used as input to the model. In Ponnani and Purathur regions, salinity and electrical conductivity was also found to be higher than the standard limits for drinking water. The salinity level in the pre-monsoon period is even higher (1500 ppm) than the recommended limits for irrigation. Data on hydrogeological parameters and aquifer properties needed as the input for the modelwere also collected from different sources. In subsurface research, the use of contaminant transport models was fully supported in the context of ground water quality.The model was developed and calibrated with 7 years data (2012 to 2018) and validated with 3 years data (2019 to 2021). After validation, the model was used for prediction. Prediction was done for 10 years by increasing the pumping rate by 5, 10 and 15 per cent of pumping rate during the validation period (2021). It was observed that the saline water intrusion is present in the coastal stretch of Padinjarekkara,Purathur and Ponnani regions of Bharathapuzha river basinwhich extends along the coast from the northern boundary of Bharathapuzha river basin. It was also predicted from the model study that the saline water intrusion reaches to a lateral distance of 4.8 km to 5.5 km from the coast along the course of river. In the current climate change scenario, global warming and the related sea level rise pose a serious concern and are a major contributor to saline water intrusion into coastal freshwater aquifers. The activities carried out in the river basin that damage the area and facilitate the movement of contaminants including sand mining from Bharathapuzha and various types of developmental activity like construction, small-scale industry, and agriculture along the coast accelerates the saline water intrusion in this area.To minimize salt water intrusion, groundwater pumping in coastal areas (up to 5.5 km from the coast) need to be restricted