What are streams that feed into the main river referred to as?

Streams that feed into the main river are known as tributaries. This term specifically describes smaller rivers or streams that flow into a larger river, contributing to its flow and drainage basin. The existence of tributaries is crucial for the hydrology of a river system, as they help gather water from various geographical areas, increasing the volume of water in the main river.

The concept of tributaries is essential in understanding river systems, as they influence the water level, ecosystem, and sediment transport within the main river. The role of tributaries highlights the interconnectedness of waterways - they act as vital branches of a river system.

The other terms, while related to water flow, refer to different features or processes. Distributaries are streams that branch off from the main river and flow away from it, typically found in delta regions. Channels refer generally to the physical pathways through which water flows, while rivulets denote very small streams or brooks that are often tributaries themselves but do not specifically imply the relationship to the main river as tributaries do.