Final answer:
Flowing water deposits the largest particles first due to sedimentation, where larger particles settle faster as water slows. This process occurs more as rivers widen and slow down, or in sedimentation tanks, and is influenced by factors like gravity and particle size.
Step-by-step explanation:
Flowing water deposits the largest particles first due to a process known as sedimentation. This occurs because larger particles, which form from aggregates of smaller ones, often known as floc, have greater weight and therefore settle to the bottom more quickly when the water flow slows. As a river or stream moves away from its source, it typically widens and slows due to decreased gradients and increased volumes of water from tributaries. This reduction in velocity reduces the water's capacity to carry large particles, causing them to settle to the bottom.
Sedimentation can happen in natural settings like rivers and lakes, as well as in man-made sedimentation tanks. In rivers, sediment moves up the shallow side of ripple marks and gets deposited on the steeper side. The water slows down even more, causing more sedimentation. In lakes, sediment can take days to settle after being deposited on the surface due to a lower terminal velocity. Finally, factors such as gravitational pull, particle size, and water flow dynamics all contribute to the phenomenon wherein larger particles settle first before smaller particles.