Arunachal Pradesh chief minister Pema Khandu’s defence of the proposed Siang Upper Multipurpose Project has shifted attention from headline-generating power capacity to a less visible but more consequential measure: how much water a reservoir can actually retain and regulate. The argument comes as public debate and protests continue in Upper Siang over pre-feasibility survey activities for the 11,000-megawatt project.
Khandu said the comparison between India’s proposed project and China’s reported 60,000-megawatt Medog dam on the Yarlung Tsangpo River is being misunderstood when it is framed only through installed generation capacity. According to figures cited by him, the Medog project has around 5.5 billion cubic metres of estimated storage, while the Siang Upper Multipurpose Project, or SUMP, has around 9.2 billion cubic metres of live storage.
His central point is that megawatts and water storage measure different things. Installed capacity indicates the maximum rate at which a hydropower facility can generate electricity under designed operating conditions. Live storage refers to the volume of water available for operational management. A project can therefore have a very high power rating without holding a proportionately large volume of water, or a lower power rating with greater storage.
That distinction matters because the public debate around SUMP has been driven partly by the apparent imbalance between the two projects. If the Chinese project is described as nearly six times larger in installed capacity, the immediate assumption may be that it would also control a far greater volume of water. Khandu’s argument is that the storage figures cited do not support that conclusion. On the numbers he presented, SUMP’s live storage would be higher than the Medog project’s estimated storage despite its lower generation capacity.
The technical explanation rests on hydraulic head, or the elevation difference through which water falls before reaching the turbines. Khandu said the steep elevation decline at the Great Bend of the Yarlung Tsangpo in Tibet enables China to generate substantial power without requiring an equivalent volume of impounded water. In practical terms, the amount of electricity a hydropower project can produce depends not only on the amount of water available but also on the height through which that water moves and the efficiency and design of the generating system.
This is why capacity cannot be treated as a direct proxy for downstream water control. A power project designed around a significant elevation drop may produce large amounts of electricity from a comparatively smaller reservoir. A multipurpose project with a larger live-storage component may have a different operating logic, balancing electricity generation with water retention and release management. The figures cited by the chief minister describe that difference, although they do not by themselves establish how either project would operate during every possible hydrological event.
Khandu used two Arunachal Pradesh projects in Dibang Valley to illustrate the same point. The proposed 3,097-megawatt Etalin Hydroelectric Project was cited as having only 7.5 million cubic metres of storage, while the 2,880-megawatt Dibang Multipurpose Project was described as having around 4 billion cubic metres of reservoir storage. The comparison places a much smaller storage figure alongside a higher installed capacity in one case, and a substantially larger storage figure alongside a lower capacity in the other.
The comparison is useful because it brings an abstract engineering distinction into the geography of Arunachal Pradesh itself. It shows that even within the same state, projects with similar broad purposes can have sharply different relationships between generation capacity and storage. The numbers also demonstrate why a single power figure cannot answer questions about flood moderation, seasonal water management or the ability to regulate downstream flows.
At the same time, the storage argument does not settle the wider dispute over SUMP. The chief minister’s statement responds to concerns about the hydrological implications of upstream Chinese projects and the ability of an Indian project to act as a downstream buffer. But the supplied account does not provide the project’s full operating rules, reservoir design, release schedules, environmental assessment findings, land requirements or details of how communities in Upper Siang would be affected.
That distinction is important for the public debate. Storage capacity is one part of a project’s physical and institutional design. Whether storage can be used as a buffer depends on how much of it is live storage, how the reservoir is operated, what inflows are expected, how quickly water can be released, and which agency controls decisions. The available account identifies the live-storage figures cited by Khandu but does not establish the proposed project’s complete operating framework.
The controversy also highlights the different stages of infrastructure decision-making. The immediate trigger for protests in Upper Siang is reported to be pre-feasibility survey activity. A survey is not the same as completed construction, but it can be experienced by local residents as the first visible step towards a major intervention in land, rivers and settlements. That makes the process surrounding surveys—notice, access, communication and consultation—part of the project’s political and administrative viability, even before final approvals are considered.
For a project of this scale, the institutional question is therefore as significant as the engineering comparison. The state government is presenting SUMP as a strategic and hydrological buffer, while residents and other critics are contesting the implications of survey activity. The supplied report does not include the protesters’ detailed demands or the government’s response to those demands. It does, however, show that the project is being debated simultaneously as an energy scheme, a water-management asset and a response to upstream infrastructure beyond India’s control.
The numbers cited by Khandu clarify one narrow but important issue: a 60,000-megawatt facility is not automatically a 60,000-megawatt water-storage system, and an 11,000-megawatt project may have greater live storage than a much larger generating facility. That is a technically meaningful correction to a common comparison. It should not, however, be mistaken for a complete assessment of downstream safety or project feasibility.
The next phase of the debate will depend on information that is not contained in the chief minister’s statement: the project’s detailed design, the basis for its storage estimates, its proposed operating protocols and the process governing pre-feasibility surveys in Upper Siang. Until those details are publicly examined, the storage comparison can explain the physics of the proposal, but cannot by itself resolve the larger question of how the project would affect the river and the people living along it.