West Bengal

West Bengal's coastline is the landward edge of one of the most extraordinary tidal systems on Earth. The Ganges-Brahmaputra delta — the Sundarbans — is the world's largest active tidal delta: roughly 10,000 square kilometres of mangrove forest, tidal creek, mudflat, and estuarine island straddling the India-Bangladesh border, the whole system built from the sediment load of two of Asia's great river systems and rearranged on every tidal cycle. The tidal regime in the Hooghly River and the Sundarbans channels is semidiurnal with a mean spring range of 4 to 5 m — macrotidal by any standard, exceptional for a delta system, and the engine that drives the ecology and the human geography of the entire coast. The Hooghly River, the westernmost distributary of the Ganga, carries the tidal signal from the Bay of Bengal 100 kilometres upstream to the Kolkata waterfront. Diamond Harbour, 50 kilometres south of Kolkata on the western bank of the Hooghly, sits at the point where the river channel begins to narrow and the tidal effect becomes concentrated: the water level swing here is fully macrotidal, and the river traffic that moves between Kolkata port and the bay — ferries, fishing boats, cargo barges — organises entirely around tidal windows. The Sundarbans mangrove system has been a UNESCO World Heritage Site since 1987. It is also one of the few places on Earth where Bengal tigers inhabit a tidal ecosystem, swimming between islands and hunting in the intertidal zone. Crocodiles — both mugger and saltwater — are present through the system. The ecological richness and the wildlife hazards are both products of the same tidal flushing that makes the Sundarbans one of the world's most productive estuaries. The India Meteorological Department and the Kolkata Port Trust operate the principal tide gauging and river-level infrastructure for this coast. National Institute of Ocean Technology (NIOT) data covers the offshore Bay of Bengal approach. Open-Meteo Marine model predictions for this region are accurate typically within plus or minus 45 minutes on timing and 0.2 to 0.3 m on height — useful for planning, with the official NIOT and IMD data as the reference for navigation and safety-critical decisions.