Sandipan Ghosh

Intensive sand mining has emerged as a dominant anthropogenic driver altering the geomorphic stability of alluvial rivers in the Anthropocene. According to the study, sand mining in the Lower Damodar Valley is now a significant geomorphic force that is similar to hydrological variability and significantly alters the shape of channels. Using multi‐temporal satellite imagery (1975–2025), field observations, and reach‐wise geomorphic assessment, the study evaluates two pronounced channel planform metamorphosis of Damodar River – (a) Downstream: transitioning from a relatively stable single‐thread to a progressively unstable and locally braided channel pattern; and (b) Upstream: transitioning from braiding to a deeply incised straight channel pattern. Excessive sand extraction has disrupted sediment–discharge equilibrium, resulting in channel incision, bed degradation, bank erosion, and bar destabilization. In several channel segments, thresholds have been exceeded, producing nonlinear channel responses (quasi‐equilibrium to chaos) in the Anthropocene River. A mining intensity threshold exceeding 1.5 was identified as the critical limit triggering systemic sediment starvation, evidenced by a sharp decline in sediment flux from ~282,000 to ~122,000 tons/year and a cumulative riverbed incision of 16.19 m (mean bed‐level decline: −0.62 m/year), collectively indicating a severe departure from geomorphic steady‐state equilibrium. High Shannon entropy (H > 2.0) in the lower Damodar River indicates highly responsive reaches with unstable sinuosity and braiding, whereas lower entropy reflects constrained channel forms. Grain‐size analysis shows depletion of medium sand (~30%) and increased gravel lag (> 38%), producing bed armoring, elevated Coefficient of Uniformity (C _u 13.0–16.0), and low Coefficient of Curvature (C _c < 0.5) indicate poorly graded, gap‐graded sediments and disrupted sediment continuity. Chaos analysis reveals nonlinear morphodynamics in flow velocity ( λ = 0.1473) and stronger instability in bed‐level changes ( λ = 0.1570). Positive Lyapunov exponents confirm that localized sand mining amplifies minor disturbances into large‐scale channel instability, complex response, and chaotic geomorphic evolution.

Deltas are low-lying regions developed by sediment deposition where rivers converge with the ocean. These ecosystems are extremely sensitive to a variety of challenges, including both natural and man-made ones. Because of their dynamic character, vulnerability to sea-level rise, and the influence of human activity on their natural processes, they are fragile. To preserve the sustainability of deltas and the welfare of the human populations that depend on them, it is imperative that management and adaptation methods take these vulnerabilities into account. The present study incorporates emerging risks and perceptible environmental changes in the Indian Sundarbans (world largest mangrove delta) which is a vital ecological hotspot and plays a crucial role in millions of inhabitants by supporting a vast array of species, providing ecosystem services, and acting as a natural buffer against coastal disasters. Numerous environmental threats, including habitat loss and biodiversity threats, are mostly caused by human activity and climate change in the Sundarbans. Sea-level rise, growing salinity, frequent floods and cyclones, pollution, and freshwater scarcity are some of these. To provide a comprehensive understanding of the growing risk in the Indian Sundarbans (Southern 24-Parganas, West Bengal, India), this chapter applies a selection of authenticated secondary database, remote sensing techniques and models. The present investigation advances knowledge of the fragile ecology of the Sundarbans by enabling long-term monitoring of changes in climate factors, sea-level rise, salinity, and biodiversity. For well-informed decisions on the management and conservation of this priceless ecosystem, this knowledge is essential.

Deltas remain a key environment for human development and support. Alongside, deltas are key drivers of the global economy and the destination of the largest migration of humans in history. Thus, humid tropical deltas offer a vast scope for researchers to deal with the dynamics of delta building in the Anthropocene, including special insights into socioeconomic heterogeneity and environmental hazards or crises. A succinct overview of these deltas comprises their geomorphic structure, historical progression, ecological and economic values, challenges and the livelihood of people chronicled in this chapter. This work contributes to a better understanding of the entangled constellation of climate change and geo-environmental dynamics together with the diverse socioeconomic aspirations and ecological fragility. Therefore, the definition and contextualization of the term delta crisis, as well as the worldwide relevance of deltas in terms of geography, ecology, and socioeconomics, are widely noted. This chapter begins with the exploration of the environmental implications of delta’s fragility and vulnerability, looking at aspects like changes in sedimentation patterns, saline intrusion, climate change, and rising sea levels. The outline of human aspects is examined here, which will look into how industrialization, urbanization, and population increase have affected the delta environment. Subsequent sections explore the socioeconomic repercussions of deltaic issues, taking into account problems such as displaced people, jobs lost, resources depleted, and the wider effects on communities reliant on deltaic resources for better deltaic sustainability. The main objective of this chapter is to build “Inventories of Tropical Deltas” by conducting an extensive review of the literature. The broad overview of the delta fragility is sketched out in the global context with an emphasis on tropical deltas because of their huge population pressures, alteration of delta building forms and processes, and socio-ecological transformation with time and space. Thus, this chapter highlights an integrated perspective on the delta from delta fragility to suitability through a structured pathway. The next chapters are connected with this goal for a better and common future of the global tropical deltas.

Tropical deltas of the world are in decline and are threatened by climate change, geo-environmental dynamics, natural hazards, and disasters. This book is a

The analysis of fluvial system anomalies is crucial for understanding the topographic evolution of the Darjeeling Sikkim Himalaya (DSH) orogen, due to the propensity of bedrock river networks to gradually shape mountain surfaces and retain evidence of landscape changes. In this study, the quantitative dimension of tectonic geomorphology has been applied utilizing the MATLAB-based Topo Toolbox 2. Chi plot, knickpoint finder, stream power incision model, stream-length gradient index, and hypsometric integral functions of Topo Toolbox 2 were used. Results revealed that geomorphic markers and fluvial anomalies provide distinct insights into the active tectonic regime, influencing (1) deviations in equilibrium channel form, (2) the sensitivity of equilibrium channel gradient to uplift rate, and (3) equilibrium fluvial relief in active collision zones. Potential areas of significant tectonic stress on stream profiles and prospective epicentres of major earthquakes are delineated as three distinct windows of the DSH: (1) the Rangit Window encompassing Jorethang and the Darjeeling Klippe in the southwest; (2) the eastern and northeastern regions of Kalimpong and the Tista Half Window; and (3) the eastern section of Gangtok and the Nathang Valley. This study additionally identified the potential zone of Holocene deformation in the piedmont fans surrounding the Matiali, Chalsa, Nagrakata, and Taljhora faults, including fault scarps, deformed sedimentary layers, triangular facets, and elevated terraces. The tectonically active DSH landscapes face a seismic risk of a significant earthquake, with a magnitude greater than 8.0, occurring after a seismic interval exceeding 200 years.