(a) How is unscientific development of catchments situated in mountainous regions responsible for increased threat of floods in…

(a) Unscientific catchment development and plains flooding

Clearing forest, cutting hill slopes for roads and building on steep catchments cut infiltration, so rain turns quickly into surface runoff and floods peak sooner and higher. Unstable slopes, undercut road cuts and badly built terraces cause landslides and erosion, which load mountain streams with sediment.

When these streams reach the plains the gradient falls, the sediment settles and the riverbed rises (aggradation), reducing channel capacity so that smaller discharges overtop banks. Construction on floodplains and the loss of wetlands remove natural storage. Landslide dams and debris flows, as in the 2013 and 2021 Uttarakhand disasters, add sudden surges. The result is more frequent flooding, avulsion and bank breaches in the Ganga and Kosi plains.

(b) Radioactive wastes and their disposal

By activity, heat and half-life, wastes are classified as: exempt or very-low-level waste, from slightly contaminated soil and rubble; low-level waste (LLW), such as contaminated clothing, tools and filters from hospitals, laboratories and reactors, with short-lived radionuclides; intermediate-level waste (ILW), such as resins, sludge and reactor components needing shielding but little heat management; and high-level waste (HLW), either spent fuel or the liquid raffinate from reprocessing, highly radioactive and heat-generating, with long-lived actinides and fission products.

Disposal follows activity. Very-low and low-level wastes go to near-surface engineered facilities, trenches or concrete vaults with multiple barriers; India has such facilities at Tarapur and Kalpakkam, among others. Short-lived ILW is conditioned in cement and held in engineered vaults. Liquid HLW is vitrified, melted with borosilicate glass and poured into stainless-steel canisters, then stored in interim facilities for decades to cool, as at Tarapur, Trombay and Kalpakkam, because India reprocesses fuel. The final solution for HLW and long-lived waste is a deep geological repository, several hundred metres down in stable rock such as granite, basalt or salt, with a multi-barrier system of glass, canister, bentonite buffer and host rock. India has not yet built one. Short-lived waste may also be allowed to decay in storage before release.

(c) Waterlogging and its control

Waterlogging is the condition in which the soil is saturated and the water table rises into or close to the root zone, excluding air from roots and reducing yield. Causes include seepage from unlined canals, over-irrigation, poor drainage, flat terrain and impervious sub-layers. Rising groundwater brings salts upward by capillarity, and evaporation leaves them at the surface, causing salinity or, with sodium, sodicity.

Remedial measures:

Drainage: surface drains remove excess water; subsurface drains of perforated pipe lowers the water table; vertical drainage by tubewells (conjunctive use) pumps groundwater and supplements irrigation.

Canal and water management: lining canals and distributaries, proper scheduling and efficient methods such as drip and sprinkler cut recharge.

Biological: biodrainage with deep-rooted, high-transpiration trees such as Eucalyptus along canals; salt-tolerant crops (barley, mustard), and green manures.

Chemical: leaching with good-quality water flushes soluble salts below the root zone through drains; for sodic soils gypsum or pyrites replace exchangeable sodium with calcium.