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Why do many parts of the Bangladesh portion of the Ganges delta flood during the rainy season?

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Physical map showing the Brahmaputra and Ganges river basins and their drainage networks across northern India, Bangladesh, Nepal, Bhutan, Tibet (China), and Myanmar. The map uses color shading to indicate elevation, from the high Himalayas in brown and white to lowland plains in green, and marks major rivers, tributaries, glaciers, dams, irrigated areas, and regions subject to flooding. An inset locator map highlights the region within South Asia. — Ganges River The Brahmaputra and Ganges river basins and their drainage network.

During the rainy season, which occurs from June to October, large portions of the Ganges delta in Bangladesh experience significant flooding, often reaching depths of 3 feet (1 meter) or more.1

This seasonal flooding is primarily driven by the region's heavy rainfall and the influence of the monsoons, which cause the river's volume to increase markedly. Because the rivers in the Bangladeshi delta region are broad and active, they carry large volumes of water that naturally inundate the low-lying landscape. In response to this recurring environmental reality, local communities have adapted by building their villages and homesteads on artificially raised land, which remains isolated above the floodwaters during the rainy months.1