Dive into Freshwater Ecology 2026 – Make Waves in Your Practice Test!

In a flowing river, velocity is not the same everywhere. The outer bank of a bend faces the fastest flow, which creates higher shear stress that undercuts and erodes the bank. This active erosion at the outer bend defines an erosional zone. Depositional zones, by contrast, form where the flow slows on the inner bend and sediments settle. A riffle describes a shallow, turbulent stretch rather than a specific erosion hotspot, and a lotic ecosystem is the broad category of any flowing-water system, not a named erosion zone. So the scenario of a fast-moving outer bank and erosion aligns with the erosional zone.