Reasons for the heavy population in the Ganga-Brahmaputra plains of India:

1. Fertile Soil: The Ganga-Brahmaputra plains have some of the most fertile alluvial soil in the world. The constant deposition of silt by the rivers has created a highly productive agricultural region. The availability of rich soil has attracted farmers and led to extensive cultivation, which in turn supports a dense population.

2. Availability of Water: The region is blessed with abundant water resources due to the presence of two major rivers, the Ganga and the Brahmaputra, along with their tributaries. These rivers provide a reliable source of water for irrigation, fishing, and transportation. The availability of water for agriculture has facilitated the growth of multiple crops and supported the livelihoods of millions of people.

3. Transportation and Trade: The Ganga-Brahmaputra plains have a dense network of rivers and canals, which serve as natural transportation routes. This facilitates trade and commerce, making it easier for people to access markets and transport goods. The availability of transportation infrastructure has encouraged the establishment of industries, leading to increased job opportunities and attracting migrants from other parts of the country.

4. Climate: The region experiences a favorable climate for agriculture, with a long growing season and adequate rainfall. The moderate temperature and availability of water make it suitable for the cultivation of a variety of crops. This favorable climate has contributed to the high agricultural productivity and attracted settlers over the years.

5. Urbanization: The Ganga-Brahmaputra plains are home to several major cities, including Kolkata, Patna, and Dhaka. These urban centers act as hubs for economic activities, education, healthcare, and administration. The presence of these cities has led to an influx of people seeking better opportunities, resulting in a high population density in the region.

6. Cultural Significance: The Ganga-Brahmaputra plains hold immense cultural and religious significance for Hindus. The rivers are considered sacred, and millions of pilgrims visit the region for religious rituals and ceremonies. The cultural significance of the region has also attracted people to settle and contribute to its population growth.

Overall, the combination of fertile soil, abundant water resources, favorable climate, transportation facilities, urbanization, and cultural significance has led to the heavy population in the Ganga-Brahmaputra plains of India.