Answer:
A. Ground Water return back to land -> Groundwater runoff
B. Falling rainwater that gets absorbed -> Subsurface runoff
C. Falling Rainwater that flows over the ground -> Surface Runoff
D. Water that percolates into the aquifer -> Ground water discharge
Explanation:
A. Groundwater that returns back to the mainland is known as groundwater discharge. It measures the entire volumetric flow of groundwater that flows back to the land bodies. Just like visible water bodies like lakes, ponds, and streams, there are also large water bodies underneath the ground. These water bodies contribute to the large volumes of water in lakes and streams that we see above the surface as groundwater makes its way back to the mainland.
B. Subsurface runoff measures the volume of water that doesn't flow over the surface but rather penetrates the unsaturated soil underneath the main surface layer. This happens when there is a large amount of water on the surface and due to lower soil pressure, soil moisture and other factors, the water gets absorbed into the lower layers and becomes part of the groundwater.
C. Surface runoff is the volume of water that flows over the land surface, without any sort of penetration into the lower layers, towards water bodies. This usually happens when there is excess water that falls onto surface land in a small period of time. This usually happens because of rain, storms or flooding as the flow of water above the surface is much faster than the rate at which it can seep into the ground.
D. Groundwater runoff dictates the flow of ground water back to its source through an aquifer in the ground. Ground water discharge is specific and unique in the sense that it only includes the discharge when an aquifer has been penetrated. This is not restricted to any singular method of returning water but only measures the overall flow.
