| A | B |
|---|
| runoff | water that flows on the surface of the ground instead of soaking into it |
| tributary | a small stream or river that flows into a larger one |
| watershed | the land area that supplies water to a river |
| headwaters | the many small streams that come together at the beginning of a river |
| floodplain | a broad, flat valley that a river flows through |
| mouth | the end of a river, where it empties into another body of water |
| reservoir | a man-made lake that stores water for human use |
| wetland | an area that is covered with a shallow layer of water during some or all of the year |
| water table | the top of the groundwater that is in an aquifer |
| aquifer | a layer of rock or soil underground that stores groundwater |
