Geography Erosion study of Subansiri river A changing coastline Glacial Meltwater Study
Erosion study of Subansiri river

Dhrubajyoti Saharia and coworkers carry out a riverbank erosion study of the Subansiri river, located in Assam (India). Their study reveals some interesting facts about this river of this flood-prone state. This work is published in the journal Applied Geomatics.

Kusumbor Bordoloi1,2,Bhaskar Ramachandra Nikam1, S K Srivastav1, and Dhrubajyoti Sahariah
from other institution  2 also from other Department of Geography, GU

Riverbank erosion is one of the key geomorphological problems encountered in the floodplains of the alluvial rivers. Many recent studies on fluvial dynamics have indicated advantages of geospatial technology over traditional techniques in terms of time, cost, and practical usability by the end-users. This study aims to assess the riverbank erosion and erosion probability in a highly dynamic and unstable stretch of the Subansiri River in Assam (India) using geospatial approach along with the Graf’s model. Temporal Landsat datasets for a period of 29 years (1989 to 2017) in time step of 4–5 years are used for mapping the river channels (active floodplains) of the Subansiri River. These river channel datasets were then analyzed to spatially quantify the erosion/aggradation and identify the high riverbank erosion zones. Identification and analysis of the high riverbank erosion zones revealed a general westward shift of the Subansiri River during the studied period. The Graf’s model, used for estimating the riverbank erosion probability, is implemented in geographical information system (GIS). The transition probability matrices for riverbank erosion were generated for different time spans (1989–1994, 1994–1998, 1998–2002, 2002–2006, 2006–2010, and 2010–2014) using the distance to river channel and erosion/aggradation maps prepared using remote sensing data. Flood recurrence intervals of the annual floods from 1988 to 2017 were estimated using observed discharge data. The transition matrices and flood recurrence intervals were then used to calibrate the Graf’s model for estimating the probability of riverbank erosion of the Subansiri River. The results were validated with observed erosion/aggradation map of 2014–2017 time period. The study demonstrates the strength of geospatial approach for rapid assessment of riverbank erosion of alluvial channels. The calibrated Graf’s model developed in this study along with understanding of the migration behavior of the Subansiri River will be useful for taking mitigation measures and planning river management strategies.

Journal References 

How are we changing a coastline?

Ujjal Deka Baruah and his fellow researchers report the long & short time changes of the Puri Coastline due to natural and anthropogenic (human) causes using satellite imagery. This research is published in Environmental Earth Sciences.

from other institutions

The coastal regions of India are densely populated and most biological productive ecosystems which are threatened by erosion, natural disaster, and anthropogenic interferences. These threats have made priority in appraisal of shoreline dynamicity as part of sustainable management of coastal zones. The present study assessed the long- to short-term dynamicity of shoreline positions along the coast of Puri district, Odisha, India, during the past 25 years (1990–2015) using open-source multi-temporal satellite images (Landsat TM, ETM+, and OLI) and statistical-based methods (endpoint rate, linear regression rate and weighted linear regression). The long-term assessment during 1990–2015 shows that shoreline accredited at the rate of 0.3 m a−1 with estimated mean accretion and erosional rate of 1.18 m a−1 and 0.64 m a−1, respectively. A significant trend of coastal erosion is primarily observed on the northern side of Puri district coast. A cyclic pattern of accretion (during 1990–1995 and 2000–2004) and erosion (during 1995–2000 and 2009–2015) was observed during the assessment of short-term shoreline change. It exhibited significant correlation with the landfall of severe cyclones and identified cyclic phases after severe cyclonic storms, i.e., phase of erosion, phase of accretion and phase of stabilisation. Overall, the natural processes specifically the landfall of tropical cyclones and anthropogenic activities such as the construction of coastal structures, encroachment and recent construction in the coastal regulatory zone, and construction of dams in upper catchment areas are the major factors accountable for shoreline changes. The output of the research undertaken is not only crucial for monitoring the dynamism of coastal ecosystem boundaries but to enable long- to short-term coastal zone management planning in response to recently reported high erosion along the Puri coast. Moreover, the usage of open-source satellite imageries and statistical-based method provides an opportunity in developing cost-effective spatial data infrastructure for shoreline monitoring and vulnerability mapping along the coastal region. 

Hydrogeochemical study on glacial meltwater of Manimahesh Glacier in Himachal Pradesh

Ujjal Deka Baruah and his research collaborators have found some interesting facts about glacier meltwater in the Manimahesh Glacier in the Himachal Pradesh region of India. The research findings of this study is published in Proceedings of the National Academy of Sciences, India in the Physical Sciences Section (Section A).

Virendra Bahadur Singh1, Pritam Chand1, Milap Chand Sharma1, Ujjal Deka Baruah, Manoj Kumar1, Naveen Kumar1, and AL Ramanathan1
1 from other institutions

The hydrogeochemical study on glacial meltwater gives important information about the quality of meltwater and weathering processes controlling dissolved ions chemistry in the glacierized area. Anionic abundance in the Manimahesh Glacier meltwater shows a trend of HCO3- > SO42- > Cl- = NO3-, whereas cationic abundance in the meltwater shows a trend of Ca2+ > Mg2+ > K+ > Na+. On the basis of high equivalent ratios of (Ca + Mg) versus (Na + K) and (Ca + Mg) versus TZ+ (total cations) and low equivalent ratio of (Na + K) versus TZ+, carbonate-type weathering has been identified as a major hydrogeochemical process regulating solute chemistry of the Manimahesh Glacier meltwater followed by silicate weathering. About 80% of bicarbonate in the meltwater of investigation area was mainly generated from carbonate weathering, whereas 20% of bicarbonate was produced from silicate weathering. The result of statistical methods (correlation, principal component and cluster analysis) shows that meltwater quality of the Manimahesh Glacier is mainly governed by carbonate and silicate-type weathering, oxidation of pyrite, dissolution of sulphate minerals and atmospheric input. The average value of suspended sediment concentration (SSC) in the glacier meltwater was calculated to be 46 mg/l and 63 mg/l during the month of June and July 2014, respectively, showing higher concentration of SSC during the month of July (peak-flow period) followed by June (low-flow period).