Question

why are river valleys thickly populated plz answer fast

Answer 1

River valleys are thickly populated because people need water to wash clothes,water for drinking,water for taking bath,water for cooking food. 
especially river valleys are populated by villager because there is no much facilities
of water in villages till now. 

Answer 2

River valleys are areas with best conditions for human existence. The areas are normally sutable for agricultural practices. People lives around here in order to take part agriculture because the area has plenty of water. The water is vital in irrigating crops and watering animals. Also the area has deep fertile soil which encourages cultivation of crops. These factors makes people to increase population density in the region.