Soil erosion is a major issue in the Indian Himalayan region, affecting both mountainous areas and the Terai. In the Terai, significant surface soil loss is driven by factors such as sandy soils, shallow soil depth, high rainfall, and the erosive force of young rivers. Human activities, including the conversion of forests and grasslands to croplands and settlements, along with poor agricultural practices, exacerbate the problem. This pilot-scale study aimed to quantify surface soil erosion and the loss of soil organic matter and nutrients in a watershed of the eastern Himalayan Terai region of India, utilizing the Revised Universal Soil Loss Equation (RUSLE) model on a Geographic Information System (GIS) platform. The results revealed substantial soil loss (x\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{x }$$\end{document} = 32.0 Mg ha-1 yr-1), along with the removal of organic matter (x\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{x }$$\end{document} = 0.95 Mg ha-1 yr-1), available nitrogen (x\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{x }$$\end{document} = 1.49 kg ha-1 yr-1), available phosphorus (P2O5) (x\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{x }$$\end{document} = 0.50 kg ha-1 yr-1), and available potassium (K2O) (x\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{x }$$\end{document} = 5.02 kg ha-1 yr-1). Ground surveys indicated that a significant portion of the local population was directly or indirectly affected by the annual loss of fertile topsoil, with farmers, agricultural workers, and tea garden owners being the most impacted. The erosion problem of Terai region remains unheard of as it does not cause direct damage like landslides. However, loss of topsoil every year declines the land productivity and curbs the agricultural financial benefit margin. The study recommends expanding soil erosion monitoring and modelling across the entire eastern Himalayan Terai region. Being a cost and time friendly reliable method, use of RUSLE on the GIS platform can be the best option for that. With updated erosion data, comprehensive management measures can be developed involving policymakers, administrators, researchers, and local communities.

This study investigated the effect of compaction effort and soaking time on the shear strength properties of fine-grained gypsum-containing soils. The objective was to demonstrate that increasing compaction effort increases soil strength, specifically cohesion and the angle of shear strength, when subjected to soaking in freshwater. Unconsolidated undrained triaxial tests were carried out on CBR soil samples with different soaking times. The results showed a transition from brittle to ductile failure behaviour as the soaking time increased. Mohr-Coulomb failure envelopes showed reduced cohesion and angle of shear strength with increasing soak time. Regression models were developed to establish correlations between soaked and unsoaked strength parameters. Strong relationships were found between soil strength properties, compaction effort and soaking time. Empirical equations were proposed to estimate the cohesion and angle of shear strength from compaction effort and soaking time. This study highlighted the importance of considering gypsum-rich soils in civil engineering design. Gypsum dissolution during wetting significantly affected soil strength parameters. The regression models and empirical equations provide engineers with tools to assess the influence of compaction effort and soaking time on soil strength, thus aiding decision making when designing structures on gypsum-rich soils.