Final answer:
River trips include encountering turbulent rapids and calm pools, predominantly located upstream where the channel narrows and the flow rate increases. These features are due to abiotic differences along the river's course, affected by elevation, channel width, and flow speed.
Step-by-step explanation:
Rafters enjoying a mountain river trip encounter both turbulent rapids and calm pools located upstream of the turbulent areas. The varying conditions in a river are due to its abiotic features, which change along the length of the river or stream. Near the source water, the channel is narrower, and the current is faster, leading to turbulence. Further downstream, the water typically flows more slowly, creating calmer areas.
The rapid and calm areas are related to the water's flow rate and the river's channel shape. In headwater streams, which are higher in elevation and often found in steep regions, you'd expect faster flow rates and thus more turbulent rapids. Conversely, downstream sections with wider channels and slower currents foster the formation of calm pools.
Understanding the dynamics of river flow is essential for safe navigation and appreciation of the river's diverse ecosystems. Rafters use knowledge of these features to predict conditions they will encounter and to choose the safest and most enjoyable routes down the river.