Public conversation around the Siang has narrowed to a single structure, the proposed Siang Upper Multipurpose Project (SUMP), and to how best to take it forward.
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“Whatever is finally decided about the dam, the catchment above it needs attention now”
Much of the public conversation around the Siang has narrowed to a single structure, the proposed Siang Upper Multipurpose Project (SUMP), and to how best to take it forward. But it has tended to crowd out a quieter question, one that does not depend on its outcome: what is the condition of the catchment above the river, and what would it take to strengthen the basin's resilience to flood, landslide and sediment risks in a changing climate, so that any investment in the region rests on stable ground? In a young and fragile Himalayan system, resilience is shaped as much by the slopes, forests and springs of the upper catchment as by any engineering at the valley floor. This is where nature-based solutions belong in the discussion, not as a slogan, and not as a rival to build infrastructure, but as a part of the resilience portfolio we can begin on now, at lower cost and with far less regret.
The physical setting leaves little margin for error. The Siang (known as the Yarlung Tsangpo before it crosses into India) and the Brahmaputra are some of the youngest, most tectonically active, and most erosion-prone terrain on Earth. Several parts of the northeast receive roughly between 2,000 and 4,000 millimetres of rain in a year, and when that volume falls on steep, seismically stressed slopes, the river carries an extraordinary load of sediment. Although precise calculation methods differ, the Brahmaputra consistently ranks among the world’s most significant sediment-transporting river systems, carrying an estimated 402 to 710 million tons of suspended load annually (Goswami, 1985; Subramanian & Ramanathan, 1996). Climate change is accelerating these hydrological dynamics simultaneously. According to the most recent Intergovernmental Panel on Climate Change (IPCC) assessment, the region faces heavier and more erratic monsoon rains, accelerating glacial retreat, and an increased risk of Glacial Lake Outburst Floods (GLOFs) across the Hindu Kush Himalayas, representing the exact combination of environmental pressures that a degraded catchment is least equipped to absorb.
Catchment studies offer an old and well-tested response to exactly this situation: treatment should begin upstream and move downstream, because that is the direction in which damage travels. The upper areas control infiltration, the generation of sediment, and the timing of flow. When forest cover is lost on the slopes, flood peaks become larger downstream. Accelerated erosion in the headwaters leads to increased sedimentation and instability in the river channels on the plains. The most lasting results come from treating the catchment as a whole, from the upper slopes down to the valley floor, rather than from work in the lower reaches alone. A more sustainable approach moves from the ridge down toward the river.
In practice, this requires a series of interventions that are neither new nor complex. These include afforestation and assisted natural regeneration on degraded upper slopes; management of spring sheds to recharge the small mountain aquifers that supply villages and sustain rivers during dry months. an approach detailed by ICIMOD and India’s initiatives to revive Himalayan springs; bioengineering techniques for stabilising unstable slopes and gullies, including bamboo-based methods promoted under the National Bamboo Mission; and the protection and restoration of wetlands and floodplains, which help store floodwater and trap sediments before it enters the river channel. Additionally, establishing riparian buffers along riverbanks is essential. Each of these actions can be measured, implemented gradually, and importantly, each delivers benefits in its own right while helping to safeguard the larger infrastructure planned for the region.
None of these counters the importance of storage infrastructure. In many ways, it is essential for the proper functioning of such systems. The primary threat to the effective operation and lifespan of any large reservoir on a Himalayan River is sediment, the very sediment that well-maintained upper catchments help to stabilise. A reservoir in a catchment that is rapidly shedding soil will fill with sediment more quickly, lose capacity sooner, and provide less flood moderation and dry-season regulation than it was designed to offer. Therefore, catchment treatment is not in competition with a project like SUMP; rather, it is nearly a prerequisite for achieving the expected lifespan outlined in the engineering studies. Additionally, if the project does not move forward or faces significant delays, as has been the case, the investment in catchment treatment will still yield benefits, including reduced flood damage, improved groundwater recharge, more consistent lean-season flow, and enhanced livelihoods from restored forests and springs.
Nature-based solutions work best alongside large-scale storage, not in place of it. A project on the scale of SUMP brings what catchment measures alone cannot: firm power of around eleven thousand megawatts and large-scale flood-moderation capacity for the basin. These are essential functions. However, the figures involved - the modelled reductions in lean-season flow, and the projected flood benefits will be firmed up as the project's detailed technical studies are completed, which is the normal course at this stage and the step that gives the basin's communities well-grounded numbers to rely on.
The honest perspective is that flood control and water security in this basin will be achieved through a combination of approaches: catchment restoration, wetlands and floodplain management, early-warning systems for glacial and flash floods, demand-side water management, and, where evidence truly supports it, engineered storage solutions. Each of these strategies should be evaluated on its own merits, and the entire process should involve transparent studies on environmental, social, sedimentation, and GLOF impacts, with the findings made publicly available.
There is one more important reason to prioritise the catchment area, and it relates to both people and hydrology. Nature-based projects are inherently local and participatory. These initiatives are built around local participation, giving communities a direct stake in the basin's future. They provide visible benefits such as improved water in springs, greater slope stability, and income generated from the work itself, directly benefiting the villages that would otherwise bear the risks of any large-scale development. In a region, where earning and keeping local confidence is central to getting any large project right, this consideration is significant.
While we should continue to debate the dam, it’s essential to recognise that the river won’t wait for that discussion to conclude. The work of strengthening the landscape through which the river flows must begin without delay. In a delicate, transboundary Himalayan catchment area, the most sustainable resilience is developed from the ridgeline downward, not only at the dam site but throughout the entire living environment that nourishes the Siang River.
Ananya Bhatia
Climate and Development Policy Consultant)