Unearthing the struggle: Navigating Sediment Challenges in the Tropical Landscape

Water bodies comprise 70% of the Earth’s surface and are vital in shaping life and the global economy. They are essential for biological cycles and the survival of life, with sediments playing a significant role in influencing these bodies. These sediments cover two-thirds of continents and nearly the entire ocean floor, with 89% of Earth’s surface sediments supporting the biosphere and forming rocks. Human activities substantially impact sedimentation and erosion, underscoring the importance of a comprehensive understanding of our environmental impact and the interconnected relationship between the environment and humans. This holds, especially in the case of the Indian Ocean, which is a critical route for global trade, particularly in energy. The extensive and densely populated coastal areas surrounding the Indian Ocean include some of the fastest-growing regions in the world.

Globally, Asian rivers are major contributors to sediment in the world’s seas, transporting around 6300 million tonnes of silt to coastal waters annually. Between 20 and 30% of the world’s ocean sediment enters the Bay of Bengal annually, constituting 15 to 20% of the total global sediment flux. The Ganga–Brahmaputra and Indus rivers contribute about 70% of this, while the remainder originates from peninsula rivers. The Deccan Traps, prevalent in the Indian peninsula, contribute debris to these rivers. The Ganges-Brahmaputra River system experiences significant variations in silt movement daily, seasonally, and throughout the year. Notably, the Alaknanda River, a Ganga headstream, exhibits five times the global average for physical weathering and six times the global average for chemical erosion.

The flow patterns of Himalayan rivers are altered by melted snow originating from ice and glaciers, coursing through deep valleys and gorges. These swift-flowing rivers carry large sediment pieces, such as rocks, pebbles, and finer materials like sand and clay. The dynamic environment they traverse leads to substantial changes in water and silt content. Himalayan rivers are distinctive due to their ever-changing paths, scouring of beds and banks, and transportation of substantial sand-sized sediment. These unique characteristics result from hydro-climatic and morpho-tectonic conditions. As these rivers reach the Ganges plain, the reduced slope slows the flow, facilitating sediment settlement. In India, 90% of the Himalayan silt comprises quartz.

Indian rivers undergo significant seasonal variations due to the region’s diverse weather patterns. During the monsoon season, lasting four to five months, rivers experience 80–95% of their annual flow and sediment load, with heavy rains causing intense flooding. This period, marked by increased river activity, is crucial in erosion and sediment transport. The geomorphic impact of monsoonal rivers is evident during these events. India’s unique rainfall patterns have shaped its rivers’ courses to accommodate diverse flows. For instance, about 95% of the Ganges’ silt load occurs during the monsoons, with nearly half of its annual water flow happening in just one week. Interestingly, over 70% of the river’s sediment reaches the delta as silt, while only 10% is sand.

Severe storms in Indian rivers are crucial in erosion and sediment transport, affecting approximately 53% of the country’s land area with soil runoff. Periodic large floods, occurring every few years to decades, result from sediment bursts from upstream, tributaries, channel edges, and floodplains. The gradual accumulation of sediment diminishes water storage in reservoirs, as the slowed water speed complicates sediment particle movement.