Contemporary Environmental Issues II — India: Water Resource Projects (Narmada, Tehri, Almatti, Cauvery, Mahanadi) and Himalayan and North-Eastern Hydropower, Watersheds, Rainwater Harvesting and Groundwater Recharge, River Conservation (Namami Gange and the Yamuna Action Plan), Lake Restoration, Wetlands and Ramsar Sites, and Soil Erosion, Land Reclamation and Desertification

The Himalayan rivers hold most of India's untapped hydropower, but the mountains are young, steep, seismically active and prone to landslides and glacial lake outburst floods. Most projects are run-of-river schemes that divert water through long tunnels to a powerhouse downstream, leaving a stretch of river between the diversion and the powerhouse with little water. Their environmental issues include this dewatering and the loss of fish and riverine habitat; tunnelling and blasting that destabilise slopes and dry up springs; dumping of excavated muck into rivers; cumulative effects of cascades of projects that leave little free-flowing river; submergence of forests; daily flow fluctuations below peaking plants; and exposure of the projects themselves to floods and debris flows, as when the rock-and-ice avalanche in Chamoli, Uttarakhand, in February 2021 destroyed the Rishiganga project and damaged the Tapovan–Vishnugad project.

A watershed is the area draining to a common point on a stream. Watershed development treats it as a unit, from ridge to valley: on the upper slopes afforestation, contour trenches and bunds slow runoff; in the middle, terracing, contour bunding and vegetative barriers hold soil and water on farmland; and in the drainage lines gully plugs, check dams and percolation tanks store water and recharge aquifers. Community participation is central, as in Sukhomajri in Haryana, where protecting the catchment from grazing in the 1970s cut the silting of Chandigarh's Sukhna Lake, and Ralegan Siddhi in Maharashtra. The national programme, the Integrated Watershed Management Programme (2009–10), became the watershed development component of the Pradhan Mantri Krishi Sinchayee Yojana in 2015.

Rainwater harvesting collects and stores rain where it falls, either for direct use or to recharge groundwater. Rooftop systems lead rain from roofs through a first-flush diverter and filter into a storage tank or into recharge pits, trenches, shafts or old wells; the volume harvestable is catchment area × rainfall × runoff coefficient, so a 100 m² roof receiving 800 mm with a runoff coefficient of 0.8 yields 100 × 0.8 × 0.8 = 64 m³, or 64,000 litres, a year. India has a rich tradition of such systems: johads and tankas in Rajasthan (the revival of johads by Tarun Bharat Sangh brought the Arvari river back to perennial flow), eris in Tamil Nadu, ahar–pynes in south Bihar, kuls in Himachal Pradesh, zabo in Nagaland and bamboo drip irrigation in Meghalaya. Tamil Nadu made rainwater harvesting compulsory for all buildings in 2003. With groundwater, the source of most irrigation and drinking water, overdrawn in many blocks, recharge is promoted by the Central Ground Water Board's master plan for artificial recharge, the Atal Bhujal Yojana (launched in December 2019 for community groundwater management in seven states) and the Jal Shakti Abhiyan's "Catch the Rain" campaign.

River conservation began with the Ganga Action Plan, launched at Varanasi in 1986 after the Central Ganga Authority was set up in 1985, to intercept, divert and treat sewage entering the river. It was extended to other rivers as the National River Conservation Plan in 1995. The Yamuna Action Plan, begun in 1993 with Japanese loan assistance and continued in later phases concentrating on Delhi, built sewers and treatment plants in Delhi, Haryana and Uttar Pradesh. The Ganga was declared the National River in 2008, and the National Ganga River Basin Authority was formed in 2009. Namami Gange, announced in 2014 and approved in 2015 as an integrated conservation mission, is implemented by the National Mission for Clean Ganga under the National Ganga Council chaired by the Prime Minister (2016); its components are sewage treatment infrastructure (much of it built under a hybrid annuity model), control of industrial effluent, river-front and ghat development, river-surface cleaning, afforestation, biodiversity conservation, public participation, and minimum environmental flows notified for the upper Ganga in 2018. The recurring limits of these plans have been treatment capacity lagging behind sewage generation, plants that are underused or not maintained, and too little water left in the river to dilute what remains.

Eutrophication, the enrichment of water with nutrients, mainly phosphorus and nitrogen, drives lakes from the oligotrophic towards the eutrophic state: dense algal and cyanobacterial blooms, turbid water, oxygen depletion in the bottom water as the blooms decay, fish kills, toxins from some cyanobacteria and, in tropical lakes, choking mats of water hyacinth. Natural eutrophication takes millennia; cultural eutrophication from sewage, detergents and fertiliser runoff can happen in years. Phosphorus is usually the limiting nutrient in fresh water, so control of phosphorus is the heart of restoration. Indian examples include Dal Lake in Srinagar, Hussain Sagar in Hyderabad, and Bellandur in Bengaluru, whose sewage-laden water has frothed and even caught fire.

• Reduce the external load first: divert or treat sewage and control runoff from the catchment, since in-lake measures fail if nutrients keep arriving.
• Control the internal load: dredge nutrient-rich sediment, or bind phosphorus with alum or other agents so it stays in the sediment, and aerate the bottom water so it does not turn anoxic and release phosphorus.
• Remove biomass: harvest water hyacinth and other weeds, which also removes the nutrients they hold.
• Use ecological methods: constructed wetlands and floating treatment islands at inflows, restored shoreline vegetation, and biomanipulation, adjusting the fish community so that more zooplankton graze the algae.

Wetlands, among the most productive and threatened ecosystems, purify water, store floodwater, recharge aquifers, store carbon and support fisheries and waterbirds. India joined the Ramsar Convention in 1982; its first Ramsar sites were Chilika Lake and Keoladeo National Park, designated in 1981, and the largest is the Sundarbans in West Bengal, designated in 2019. The number of Indian Ramsar sites has grown rapidly since 2022, so a current count should be checked rather than memorised. Wetlands are regulated by the Wetlands (Conservation and Management) Rules, 2017, which replaced the 2010 rules and give state wetlands authorities the lead role; the National Lake Conservation Plan and the National Wetland Conservation Programme were merged in 2013 into the National Plan for Conservation of Aquatic Ecosystems. Chilika is the success story: opening a new mouth to the sea in 2000 restored salinity and fisheries, and it was removed from the Montreux Record in 2002. Loktak Lake in Manipur, still on the Montreux Record, is known for its floating mats of vegetation, the phumdis, which carry the Keibul Lamjao National Park, home of the endangered brow-antlered deer or sangai.

Soil erosion by water, as sheet, rill and gully erosion and, at its extreme, the ravines of the Chambal, Yamuna and Mahi valleys, is the most widespread form of land degradation in India; wind erosion dominates in the arid west. Its causes are deforestation, overgrazing, cultivation of steep slopes without conservation, shifting cultivation with short fallow cycles, and poor management of canal irrigation. Soil loss can be estimated with the universal soil loss equation taught in Unit II. Conservation combines agronomic measures (contour farming, strip cropping, mulching, cover crops and conservation tillage), mechanical measures (contour and graded bunds, bench terraces, gully plugs and check dams) and vegetative measures (afforestation, grass barriers and shelterbelts). A large share of India's land is degraded; India has committed to restore 26 million hectares of degraded land by 2030, a target announced when it hosted the fourteenth Conference of the Parties to the desertification convention in 2019.

Desertification, in the definition of the United Nations Convention to Combat Desertification (adopted in 1994, in force 1996), is land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors, including climatic variations and human activities; it is not the advance of existing deserts but the loss of productivity of drylands. In India it affects western Rajasthan and Gujarat most, with overgrazing, over-cultivation of marginal land, excessive groundwater use and wind erosion as its drivers. Control measures include stabilising sand dunes with grasses and shrubs and micro-windbreaks, shelterbelts of trees, rotational grazing, water harvesting and dryland farming practices, on which the Central Arid Zone Research Institute at Jodhpur has long worked; the international goal is land degradation neutrality, a target under Sustainable Development Goal 15.