Final answer:
The Yellow River is the river known for severe and sudden floods, which was managed by early farmers in South China through the creation of paddy fields and sophisticated irrigation systems.
Step-by-step explanation:
The river characterized by severe and sudden floods, which early farmers in South China learned to control by cultivating rice in paddy fields, is the Yellow River. This river has been pivotal to the development of Chinese civilization, with its fertile soil known as loess being critical to farming. The earthen dam constructed by the Zhou dynasty, around 591 BCE, is one of the earliest examples of flood management, which facilitated the cultivation of rice by diverting parts of the Yellow River. Despite the benefits that the dam and irrigation systems brought, the river was also associated with historical challenges, including devastating floods that led to environmental catastrophes, such as during Wang Mang's rule.