Assessment of the Impact of Sand Mining on the Morphology of the Severely Affected Reach of Bharathapuzha River between Pattambi and Kuttippuram Using Remote Sensing and GIS

Abstract

Rivers have been a subject of study by engineers and scientists who have been fascinated by their self-formed geometric shapes and their responses to changes in nature and human interference. Among various types of human interventions, indiscriminate extraction of sand and gravel is the most disastrous one, as it threatens the very existence of the riverine ecosystem. Bharatapuzha River in Kerala is a great victim of illegal sand mining. The effect of over exploitation of instream sand on the river morphology is very important for quantifying its effect and for exploring alternatives. The mining activity is particularly very high in the stretch between Pattambi and Kuttippuram of Bharathapuzha river. Use of remote sensing technology coupled with Geographical Information System (GIS) is a quick means of gathering latest accurate information, economically. The study was undertaken to assess the morphological changes as well as the spatial and temporal variations along the reach due to sand mining. The study utilised DEM imageries to evaluate the effect of sand mining on the morphology of the river reach by analysing the cross-sectional details. LANDSAT imageries were used to analyse the spatial and temporal variations of channel in the reach. The analysis and assessment of satellite imageries were carried out using the ArcGIS 10.5 software. The Elevation Profile add-in toolbar was utilised to create profile graphs by taking sections across the river course in ArcGIS and the morphological changes of the river were calculated by comparing the cross-section profiles. The spatial and temporal variations in river morphology were analysed by extracting the bank lines using Normalized Difference Water Index (NDWI) and overlaying the extracted bank lines. The study revealed that the impact of sand mining was high at areas closer to Kuttippuram. Channel enlargement in the reach was found to be varying from 0.52 - 8.43 m/year. The reach experienced an average rate of change in width of 0.28 m/ year. The shift in bank lines indicated the drifting of the river direction towards the north. From the study, it can be concluded that remote sensing and GIS techniques provided realistic information about the impacts of sand mining on the riverine ecosystem and have sufficient accuracy for use in morphological analysis of rivers.