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

Unscientific Development in Mountainous Catchments and Flooding in Plains

Unscientific development in mountainous catchments, particularly in the Himalayas (e.g., Uttarakhand), significantly exacerbates flood hazards in the downstream Indo-Gangetic plains. Deforestation and extensive slope destabilization drastically lower soil infiltration capacity, transforming rainfall into rapid, voluminous surface runoff. Indiscriminate hillside excavation for roads, toe erosion, and poorly engineered agricultural terracing trigger mass wasting and landslides, supplying vast sediment loads to mountain rivers.

As these sediment-laden channels enter the plains, the sudden drop in hydraulic gradient forces rapid deposition. Riverbed aggradation reduces channel cross-sectional area and carrying capacity. Concurrently, encroachment upon floodplains and degradation of natural riparian wetlands strip the basin of its buffering capacity, causing monsoon surges to breach natural levees, trigger river avulsions, and produce severe inundation across the plains.

Radioactive Wastes: Classification and Disposal Methods

Radioactive wastes are categorized according to activity level, heat generation, and radionuclide half-life:

Low-Level Waste (LLW): Contains minimal quantities of short-lived radionuclides originating from hospitals, research laboratories, and industrial cycles (e.g., contaminated protective gear, tools, wiping rags). It emits low radiation and requires no specialized shielding during handling.

Intermediate-Level Waste (ILW): Comprises materials with higher radioactivity, such as chemical sludges, ion-exchange resins, and reactor components. It requires significant radiation shielding (lead or concrete) during handling, though it generates negligible heat.

High-Level Waste (HLW): Characterized by high radioactivity and substantial decay heat, HLW arises from the nuclear fuel cycle. It is distinguished into un-reprocessed spent fuel (containing uranium, plutonium, and actinides) and reprocessed liquid waste containing concentrated fission products.

Disposal Methods: Vitrification: Liquid HLW is chemically immobilized by blending it with molten borosilicate glass matrix at high temperatures, followed by casting into heavy stainless steel canisters for initial cooling. Near-Surface Engineered Facilities: LLW and short-lived ILW are emplaced in concrete-lined vaults, trenches, and rock cavities at shallow depths (e.g., Bhabha Atomic Research Centre facilities), relying on multi-barrier engineering to prevent radionuclide migration. Deep Geological Repositories (DGR): For HLW and spent fuel, disposal involves deep underground excavations (300 to 1,000 meters) within stable, impermeable host formations such as crystalline granite, salt domes, bedded salt, or basalt. The multi-barrier system—incorporating the vitrified matrix, metallic canisters, bentonite clay backfill, and the impermeable host rock—isolates long-lived radioisotopes from the biosphere over geological timescales.

Waterlogging and Salinity: Mechanisms and Remedial Measures

Waterlogging refers to the state where the soil root zone remains saturated above field capacity, creating anaerobic conditions that starve roots of oxygen and curtail crop productivity. It is caused by excessive canal irrigation without adequate conveyance lining, poorly maintained surface drains, high regional water tables, flat topography, and impermeable subsurface claypans. Waterlogging induces secondary salinity: capillary action transports dissolved mineral salts from shallow groundwater to the surface, where intense evaporation leaves crusts of sodium, calcium, and magnesium salts.

Remedial Measures:

Biological Remediation: Biodrainage through the afforestation of high-transpiration, deep-rooted species like Eucalyptus actively lowers the water table. Incorporating salt-tolerant crops (barley, mustard) and green manures (Sesbania) improves soil organic matter, aggregation, and hydraulic conductivity.

Mechanical and Engineering Drainage: Construction of open surface drains rapidly removes storm runoff. Subsurface horizontal drainage, using perforated corrugated PVC or tile pipes wrapped in geotextile envelopes, intercepts and evacuates shallow perched water tables. Vertical drainage via battery tubewell networks pumps excess unconfined groundwater (conjunctive use), lowering the regional water table while supplementing irrigation.

Chemical and Agronomic Remediation: Leaching excess soluble salts by ponding high-quality freshwater flushes them below the active root zone through drainage outlets. For sodic soils, applying chemical amendments such as gypsum (calcium sulphate) or iron pyrites displaces exchangeable sodium cations with calcium, which are subsequently leached out, thereby restoring soil structure and infiltration rates.

Integrated Management

Catchment degradation in upper mountainous watersheds alters regional hydrological cycles and accelerates sedimentation in the plains, which in turn impairs natural surface drainage and raises groundwater tables. Mitigating these connected environmental hazards requires an integrated basin approach, combining upper-catchment slope stabilization with conjunctive water use and subsurface drainage networks across downstream agricultural plains.