Water flowing over land into streams is described by which term?

• A. Riffle
• B. Riparian Zone
• C. Ecosystem
• D. Runoff

Answer: (D)

Water moving over the land surface into streams is runoff. This describes the overland flow that happens when precipitation cannot infiltrate or evaporate quickly enough, so water travels across the ground, collects in channels, and eventually reaches streams or rivers. Runoff focuses on the surface transport of water after rainfall or snowmelt, which differentiates it from other terms. A riffle is a shallow, fast-moving part of a stream channel related to water depth and habitat for organisms; the riparian zone refers to the vegetation and soils along a waterbody that influence bank stability and shading; an ecosystem is the broader network of living organisms and their physical environment. So the best fit for the described process is runoff because it directly names the surface flow that delivers water to streams.