The quantity and seasonality of water flow in a river may greatly change from its normal condition between a major storage and downstream, thus paving the way for drastic changes in the riverine ecosystem. ‘Environmental flow’ refers to the amount of water considered sufficient for protecting the structure and function of an ecosystem and its dependent species.

The paper goes on to describe the case of river Bhadra, which is the site of a dam that has significantly altered the natural flow of the river and describes the study that aimed at conducting the environment flow analysis of the river.

This study was based on both, field investigations and desk study. The study aimed at estimating:

• The present environmental flow rates in the river
• The ideal/optimal environmental flows to be maintained in the river
• The potential benefits of these flows.

For assessing the environmental flow in the river, the Tenant method was adopted and the analysis included:

• A situation analysis
• Water utilisation patterns
• Ecology of the river
• Ecosystem services in the river basin
• Current flow regime

The study found that the present flow rates were inadequate and could have a negative effect on the river ecosystem, if the same situation prevailed. Attempts needed to be made at maintaining these flows, which would lead to long term advantages for the river ecosystem.

The paper argues that  way forward can  include implementing environmental flows that require either an active management of infrastructure such as dams, or a restrictive management, for example, through reducing the abstractions for irrigation.

However, both types of interventions depend on a change in the behaviour of people and need to be based on an informed decision that has broad societal support.