During the dry months, several rivers of Manipur tend to dry up, resulting in water scarcity in the Northeast Indian state of Manipur, which is well known for its scenic wetlands and is a feast for photographers. Some of the water bodies are dying and vanishing owing to the erratic rainfall patterns witnessed over the past few years. The alarming state of the water bodies calls for rejuvenation of rivers in the state.
It may be mentioned that over a long time, a river forms generally smooth profiles. Apart from the water needs of the people, in terms of transporting waste and sediment it is the most efficient profile to have. Rivers that have this form of profile are in balance with the environment (equilibrium).
Typically, a river will always try to form a concave shaped profile. From time to time some occurrences can change or de-stabilizes this equilibrium – a healthy ecosystem. This causes the river to vertically erode its channel to re-establish its long smooth concave profile. This renewed period of the river course is known as rejuvenation.
The river ecosystem is a complex mosaic of interaction and interrelationship of the biotic (flora and fauna) and abiotic (hydrological, geomorphic etc.) components in dynamic biodiversity equilibrium.
The ecological function of a river is linked to the hydrological variations in the river flow. Hence river water flow is the most important and significant variable of a river system or ecosystem.
Besides sustaining the ecosystem and performing its geomorphic functions (erosion, sediment transport, reworking etc.), a smooth river flow recharges groundwater in its flood plain.
During floods, the river water adds nutrients to the soil. A river is the ultimate sink for surface runoff in its basin.
In the existing development paradigm, the natural freshwater flow in the rivers has been overexploited by diversion of river water for agricultural, industrial and domestic uses.
The overexploitation of river resource is manifested mostly by lack of longitudinal, lateral and vertical connectivity in the river system and poor flow in the river. Further, contamination of the rivers by domestic and industrial liquid waste has led to the deterioration of river health. This coupled with encroachment on river space; obstruction of water ways in the drainage basin; excessive sand mining and deforestation in the catchment has further aggravated the problem.
The poor health of rivers has adversely impacted the complex dynamic equilibrium in the river basin. It raises question about sustainable use of river resource.
The concept of environmental flow in river management is already being applied in some or other form in 72 countries around the world. During the monsoon season a typical effluent stream inundates and deposits sediment load charged with flood waters in the river bank (Bank storage).
The monsoon season peak flow in the river also inundates adjacent flood plains and recharges groundwater under appropriate condition. This in the long run maintains the slope of groundwater table towards the river.
During the post monsoon seasons the same river initially receives contribution from the bank storage. This continues till the groundwater table elevation in the vicinity of the river diminishes to the regional groundwater table slope. Henceforth, the regional groundwater flow charges the river and sustains its flow.
In the monsoon, if proper environmental flow in such rivers is not maintained then the river flow contribution from the bank storage may diminish. This will also reduce flood plain inundation and recharge to the aquifers. This in turn will reduce the regional groundwater table slope towards the river, leading to flow variability in the river.
It is quite possible that river would lose longitudinal connectivity during the summer season.
In case of such deterioration in river health; a proper environmental flow during the monsoon season would lead to the rejuvenation of the river. It is required that measures based on the understanding of river ecosystem coupled with environmental flow should be integrated in the river rejuvenation efforts.
The plight of urban rivers in India has been going from bad to worse courtesy, systematic neglect and unplanned development projects. On the one hand they are being increasingly deprived of freshwater flows by diverting water for domestic supplies and on the other have been turned into dumping place for mostly untreated solid and liquid waste in massive amounts from residential areas as well as industrial pockets.
As a result, India is facing its worst water crisis in four decades. At least 54 per cent of the sub-continent has turned into a water-stressed dust bowl with many rivers rapidly drying up.
Experts opine that by 2025, the country will be facing an acute water crisis if no preventive measures are taken today. So India today is desperately in need of answers to resolve its water crisis.
The country faces a critical challenge to improve the productivity of drinking fresh water.
No socio-economic development or even political stability will ever be possible without ensuring uninterrupted supply of quality potable water.
It is, therefore, clear that river rejuvenation will need to be distributed across the country. In other words, we will need to capture rain water, where it falls, over vast parts of the country so that we can provide local water security and recharge every well.
River rejuvenation is an effort aimed at restoring poor health of overexploited and polluted rivers. It requires an understanding of the causes for the poor health and the restoration efforts from source to sink.
Depending on the level of deterioration, river rejuvenation aims at a new sustainable healthy river ecosystem. This can also be achieved by restoring the river health back to an accepted historical state of the river.
Avoiding direct entry of domestic sewage and industrial effluents into the river will certainly improve the river health.
But flow of a river is its identity and the most significant variable of a river system. Besides performing various functions, it gives self-cleaning and healing powers to a river.
Thus, the river rejuvenation broadly calls for optimal fresh water flow through the river system during different seasons.
The rejuvenation of a river is best achieved by ensuring environmental flow in the river.
To conclude, the need of the hour is environmentally sustainable development of river resource.
A process based understanding of the river ecosystem will facilitate sustainable exploitation of this resource. So that humanity can enjoy the river ecosystem benefits for several generations.
In case of the river system in poor river health, river rejuvenation can also be achieved by broadly aiming at restoring assured environmental flow in the river system.
The planners and policy makers should necessarily integrate the concept of environmental flow with water resources development strategy.
(The views expressed are personal)