Kolkata - Geography

Geography

Spread roughly north–south along the east bank of the Hooghly River, Kolkata sits within the lower Ganges Delta of eastern India; the city's elevation is 1.5–9 m (5–30 ft). Much of the city was originally a wetland that was reclaimed over the decades to accommodate a burgeoning population. The remaining undeveloped areas, known as the East Kolkata Wetlands, were designated a "wetland of international importance" by the Ramsar Convention (1975). As with most of the Indo-Gangetic Plain, the soil and water are predominantly alluvial in origin. Underlying the city are quaternary sediments consisting of clay, silt, and several grades of sand and gravel. These sediments are sandwiched between two clay beds: the lower one at a depth of 250–650 m (820–2,130 ft); the upper one 10–40 m (30–130 ft) in thickness. According to the Bureau of Indian Standards, on a scale ranging from I to V in order of increasing susceptibility to earthquakes, the city lies inside seismic zone III; according to a United Nations Development Programme report, its wind and cyclone zone is "very high damage risk".