Final answer:
Streams erode their channels through processes such as abrasion, dissolution of soluble material, and transportation of fragments.
Step-by-step explanation:
Streams erode their channels through processes such as abrasion, dissolution of soluble material, and transportation of fragments. Abrasion occurs when running water picks up and rubs against rocks and sediments, wearing them down over time. Dissolving soluble materials refers to the chemical breakdown of substances like limestone or salt, which can be carried away by the flowing water. Finally, the transportation of fragments involves the movement of eroded materials downstream, where they can be deposited in wider flood plains or other areas of a river or stream.