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.
