The top of groundwater is known as the watertable. The flow of water through a stream channel is commonly called streamflow or stream discharge. On many streams humans gauge streamflow because of the hazards that can result from too little or too much flow. Mechanical gauging devices record this information on a graph known as a hydrograph. In the online notes there is a representation of a hydrograph showing some of its typical features.
Oceans cover most of the Earth's surface.
On average, the depth of the world's oceans is about 3.9 kilometers. However, maximum depths can be greater than 11 kilometers. The distribution of land and ocean surfaces on the Earth is not homogeneous. In the Southern Hemisphere there is 4 times more ocean than land. Ratio between land and ocean is almost equal in the Northern Hemisphere.