The River Revival Puzzle
India has spent decades tackling river pollution, with growing investments in sewage treatment plants (STPs) and waste infrastructure. But a less understood and often overlooked component of river rejuvenation is environmental flow, or e-flow—the minimum flow of water that must be maintained in a river to sustain its ecological and hydrological integrity.
Even if every drop of sewage is treated, a river without natural flow is a dead channel. E-flow acts as the life force, ensuring that treated water moves, dilutes pollutants, oxygenates ecosystems, and sustains biodiversity.
What Is E-Flow?
E-flow refers to the quantity, quality, and timing of water flows required to maintain a river’s health.
According to the Central Water Commission (CWC), e-flow is the regulated release of water from dams, barrages, and reservoirs to mimic natural flow patterns. It supports:
Dilution of treated waste
E-flows can be seasonal, allowing more water during monsoons and less during lean seasons, replicating nature’s rhythm.
Why Treated Sewage Isn’t Enough
Delhi’s Yamuna stretch, especially between Wazirabad and Okhla, remains heavily polluted even after the establishment of STPs. Why?
No significant flow exists to carry treated sewage downstream
River becomes stagnant, with limited dilution or self-cleaning
Oxygen-depleted stretches harm aquatic life
Algal blooms and toxic foam form in the absence of moving water
Even treated water, if it sits in low-flow conditions, gets re-polluted by silt and industrial runoff
The Science Behind E-Flow
Rivers naturally cleanse themselves through re-aeration, dilution, and sedimentation. For these processes to function:
Minimum velocity is needed to push water forward
Depth supports fish habitats and aquatic species
Flow must fluctuate to mimic seasonal changes for breeding cycles
Without e-flow, a river becomes a stagnant canal, unable to support life or degrade pollutants effectively.
Global Examples of E-Flow in Action
Australia’s Murray-Darling Basin:
Introduced e-flow releases from dams to revive wetlands and support fisheries
E-flow legally mandated as part of national water legislation
Strategic flow management combined with sewage treatment brought the once-polluted river back to life
India’s Progress on E-Flow
The National Mission for Clean Ganga (NMCG) has mandated minimum e-flows for the Ganga under the Ganga River (Rejuvenation, Protection and Management) Authorities Order, 2016.
For the Yamuna:
A 2019 report by the CPCB stressed a minimum e-flow of 23 cubic meters per second (cumecs) between Wazirabad and Okhla
Yet, much of this is not met during the non-monsoon seasons
E-Flow After Optimal Sewage Treatment: A Synergistic Model
Optimal sewage treatment provides cleaner water, but e-flow gives that water life and mobility. Here’s how they work together:
| Component | Role |
|---|---|
| STPs | Remove harmful contaminants from sewage |
| E-flow | Dilutes, oxygenates, and disperses treated water |
| Combined Impact | Prevents stagnation, restores ecology, and supports downstream users |
This synergy can:
Revive aquatic biodiversity
Reconnect disconnected floodplains
Improve urban microclimates and aesthetics
Barriers to Implementing E-Flow
Irrigation and drinking water often prioritized over river health
Releases are based on human needs, not ecological schedules
No penalty for failing to release mandated flows
Lack of seasonal ecological benchmarks
Policy Recommendations
Legal Framework for enforcing minimum e-flows across all major rivers
Incentives for states that release and monitor ecological flows
Technological interventions like automated gates for flow regulation
Public awareness and community watchdogs for accountability
Did You Know?
India’s Rig Veda, written over 3,000 years ago, described rivers as living goddesses with a “flowing spirit.” In modern terms, e-flows can be seen as reviving this spirit by restoring the river’s natural breath and rhythm.
Conclusion: Reimagining River Rejuvenation
India’s river restoration cannot succeed by focusing solely on treating waste. E-flow is the circulatory system that enables a river to breathe, cleanse, and thrive.
As climate change alters rainfall patterns and urbanization squeezes water resources, smart water governance must prioritize ecological needs alongside human ones.
Treated sewage is a start—but e-flow is the finishing stroke that turns cleaned drains into living rivers.
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