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Conservation of embankment soil along the rivers is a global challenge. The existing solutions including rigid structures and cement-based techniques pose risks to the sensitive river ecology. The trending biopolymer (Bp) based soil stabilisation technique has shown enormous potential to stabilise loose and soft soils. The rheology of such biopolymer solutions is expected to play a critical role in soil stabilisation, especially in a wet environment such as riverbanks. In this study, four different levels of xanthan gum treatment (0.5 to 1.25% by soil weight) are investigated for stabilising the soil collected from an erosion-prone bank of the Brahmaputra River basin. The rheological properties of the intended biopolymer solutions are investigated extensively prior to their application. Later, the degree of stabilisation of the biopolymer-treated soil is determined by evaluating their unconfined compressive strength (UCS) and secant modulus. The erosion characteristics of the treated samples were evaluated using an in-house built apparatus. The shear-thinning and viscoelastic parameters of the biopolymer solutions have been quantified with the rheological analysis. The UCS strength test revealed a consistent increase up to 1.6 MPa with an increase in the biopolymer treatment of 1.25%. The erosion test revealed that the biopolymer treatment delayed the erosion process. However, it did not completely cease the erosion. The microstructure analysis revealed that the strong biopolymer bridging acts as a dampener in the soil pores to delay erosion. This study unravels the critical role of rheological factors, which are essential in reproducing the desired results from the geotechnical laboratories to field-scale applications. [ABSTRACT FROM AUTHOR]

Increased frequency of extreme weather events has made the conservation of riverbanks and coastlines a global concern. Soil stabilisation via microbially induced calcite precipitation (MICP) is one of the most eco-suitable candidates for improving resilience against erosion. In this study, the erosion characteristics of soil treated with various levels of biocementation are investigated. The samples were subjected to hydraulic flow in both tangential and perpendicular directions in a flume to simulate riverbank and coastal situations. Soil mass loss, eroded volume, and cumulative erosion rates of the treated soil against the applied hydraulic energy density have been reported. Post erosion exposure, the residual soil has been assessed for its properties using needle penetration resistance, precipitated calcium carbonate content and microstructure. It was observed that soil erosion declined exponentially with the increase in calcium carbonate content against the perpendicular waves. However, biocementation leads to brittle fracture beyond a threshold, limiting its efficacy, especially against the tangential waves. Additional composite treatment with a biopolymer was found to improve the resilience of the soil specimens against erosion. The composite treatment required half of the quantity of the biocementing reagents in comparison to the equally erosion-resistant plain biocemented sample. Therefore, stoichiometrically the composite treatment is likely to yield 50% lesser ammonia than plain biocement treatment. This investigation unravels a promising soil conservation technique via the composite effect of biocement and biopolymer. [ABSTRACT FROM AUTHOR]

The Brahmaputra is a unique dynamic river in the world with intense braiding and critical bank erosion. Both erosion and deposition are continuous processes in the river in an attempt to reach a new equilibrium in channel geometry and morphology by the ever dynamic nature of flow. Erosion and deposition of the river have link to land use and land cover (LULC) as the land cover is under constant change in a dynamic landscape constantly shaped by continuous erosion and deposition. The objective of the present work is to evaluate the extent of erosion and deposition along the Brahmaputra river and change in the LULC of the Brahmaputra river in Assam, India. Remote sensing and geographic information system (GIS) techniques were utilised to extract information from Landsat images. Total area of erosion and deposition during 1973–2014 was 1557 and 204 km2, respectively. Increase in area (28%) of the Brahmaputra during 1973–2014 is not solely due to bank erosion, but also for the bifurcation of streams without the loss of land. LULC study has revealed that 29% area was occupied by active channels and 71% was occupied by bars in 2014. Maximum reaches experienced reduction of the submerged part in 2014 compared to 1994 in the post-monsoon months with an overall decrease from 37% to 29%. A reduction in natural grassland and forest has been observed with a corresponding increase in agricultural practices in different bars and islands of the Brahmaputra in Assam during 1994–2014. [ABSTRACT FROM AUTHOR]