BharatNotes What is Environmental Flow (E-Flow)?
Environmental Flow (E-Flow) refers to the quantity, timing and quality of water that must keep flowing in a river to sustain its aquatic ecosystems and the human cultures, economies and livelihoods that depend on them. The widely used definition comes from the Brisbane Declaration (2007, updated 2018), which framed e-flows as the flows "necessary to sustain aquatic ecosystems which, in turn, support human cultures, economies, sustainable livelihoods, and well-being."
A river is not merely a channel for water supply; it is a living ecosystem. When dams, barrages and diversions for irrigation, hydropower and industry capture too much water, downstream stretches can dry up, harming fish, riverbed recharge and dependent communities. E-Flow is the regime designed to prevent this by guaranteeing a science-based minimum flow throughout the year.
E-Flow Norms for the Ganga (2018 Notification)
Through a Gazette Notification dated 9 October 2018, the Government of India mandated minimum e-flows for the Ganga, implemented under the Namami Gange programme. The norms cover the Upper Ganga Basin from its originating glaciers through Devaprayag up to Haridwar, and the main stem up to Unnao district (Uttar Pradesh).
For the Upper Ganga, the mandated minimum e-flow (as a percentage of the monthly average flow) is set season-wise:
| Season | Months | Minimum E-Flow |
|---|---|---|
| Dry | November – March | 20% |
| Lean | April – May (and October) | 25% |
| High flow / Monsoon | June – September | 30% |
(Source: Gazette Notification, 9 October 2018.) All existing, under-construction and future projects are covered; existing projects were given three years to modify designs to comply.
Monitoring and Governance
The Central Water Commission (CWC) is the designated authority and custodian of flow data, responsible for supervision, monitoring and regulation, submitting a quarterly compliance report to the National Mission for Clean Ganga (NMCG).
To strengthen oversight, NMCG launched the E-Flow Monitoring System on 13 June 2024 as part of the Aviral Ganga component and the PRAYAG real-time monitoring portal. The system tracks in-flow, out-flow and mandated e-flow across 11 projects along the Ganga main stem, using CWC's quarterly data.
Significance and Limitations
E-Flow operationalises the "Aviral Dhara" (continuous flow) objective alongside "Nirmal Dhara" (clean flow) for the Ganga. It balances developmental water demands with ecological survival, sediment transport, groundwater recharge and the cultural needs of riparian communities.
Critics, however, have argued that the percentages are modest and that the notification's framing leaves room for under-compliance, with monitoring data showing violations in early years. The concept also informs broader debates on river rejuvenation across India.
UPSC relevance: Foundation concept for GS3 — underpins questions on river rejuvenation, the Namami Gange programme, dam–ecology trade-offs and sustainable water-resource management. Pair it with Aviral/Nirmal Dhara and the CWC–NMCG governance split for high-value Mains answers.
