Patna: Despite Bihar and Patna recording a rainfall deficit, the Ganga has risen above the danger mark at several locations in the city with experts attributing the rise to rainfall in upstream catchments, including parts of Nepal and the Himalayan region.Atul Aditya Pandey, professor and former head of the geology department at Patna University, said the Ganga receives substantial inflow from tributaries on both its northern and southern sides. Rivers such as the Gandak, Kosi and Mahananda have catchments extending into Nepal and the Himalayan region, allowing heavy rainfall there to increase downstream flows in Bihar.The Sone, another major tributary, originates in Madhya Pradesh and drains parts of Madhya Pradesh, Uttar Pradesh and Jharkhand before entering Bihar.“Patna has a unique location. Several major rivers meet the Ganga within a relatively short stretch from Maner to Bakhtiyarpur. This brings excess water as well as sediment into the river system,” he said.Pandey said sediment deposition over time can make the river channel shallower, reducing its capacity to carry floodwater and causing water to spread over a larger area.A hydrometeorologist at the India Meteorological Department, Patna, said the Ganga can continue to rise even as the Punpun and Sone fall because it receives water from a much larger upstream catchment. While the Ganga is rising at several locations in Patna, the Sone at Koelwar and Punpun at Shripalpur are falling. The contrasting trends reflect different hydrological conditions across the river systems.
