What best defines a watershed?

What best defines a watershed?

• A. An area that drains to a common outlet
• B. A type of sub-surface rock formation
• C. A political boundary of water districts
• D. A nutrient-rich zone in wetlands

Answer: (A)

Water moves across the landscape in a way that all rain falling within a certain area eventually flows to a single outlet, such as a river, lake, or ocean. The boundary of that area is set by the drainage divide, a high stretch of terrain that directs runoff toward different outlets on either side. A watershed includes not just the streams and rivers, but also the connected groundwater that feeds them, all contained within that boundary. Understanding this helps explain why activities anywhere within the area can impact water quality and supply at the outlet. Other descriptions don’t fit because they describe things unrelated to how water collects and drains—the geology of subsurface rocks, political boundaries of districts, or ecological zones in wetlands.

Water moves across the landscape in a way that all rain falling within a certain area eventually flows to a single outlet, such as a river, lake, or ocean. The boundary of that area is set by the drainage divide, a high stretch of terrain that directs runoff toward different outlets on either side. A watershed includes not just the streams and rivers, but also the connected groundwater that feeds them, all contained within that boundary. Understanding this helps explain why activities anywhere within the area can impact water quality and supply at the outlet.

Other descriptions don’t fit because they describe things unrelated to how water collects and drains—the geology of subsurface rocks, political boundaries of districts, or ecological zones in wetlands.