Environmental Flow for the Yamuna River in Delhi as an Example of Monsoon Rivers in India

With an eye on all the natural functions of a river, the present article considers the flow of the river Yamuna in Delhi as an example of monsoon rivers in India. About 80% of the total virgin flow of Indian rivers is during the monsoon period and the remaining 20% is during the non-monsoon period. In case of the river Yamuna in Delhi, we find that at least 50% of the vir-gin monsoon (July to September) flow is required for transport of the full spectrum of soil particles in the river sediment. A similar flow is needed for adequate recharge of the floodplain aquifers along the river. For the non-monsoon period (October to June), at least 60% of the virgin flow is necessary to avoid growth of still-water algae and to support river biodi-versity. We conclude that about 50-60% of the virgin flow is necessary throughout the year to maintain the health of the river system.