What Are the Differences Between Run-Off & Ground Water?

Water serves as one of the most important resources on Earth. Freshwater sources allow our survival and enable the expansion of cities, suburbs and industrial complexes. Two main components of fresh water exist in runoff and groundwater. However, these two categories of water play entirely different roles in the environment. Runoff water can be defined as surface water flow over land, while groundwater is beneath the Earth's surface.

Sources of Water

• Runoff water accumulates in rivers.

  The main difference between runoff water and groundwater lies within the source of each. Runoff water can be attributed as excess water flowing over land from excess rain, meltwater and flooding. As precipitation falls on land, rainwater hits saturated ground and collects to flow downhill over land. Water eventually flows along channels and streams, ending up in the ocean. On the other hand, groundwater makes up much of our available drinking water, and can be found in soil pore spaces and within rock formations. Aquifers hold much of the groundwater that flows underneath the surface.

Water Cycle

• Both runoff and groundwater play important, but differing roles within the water cycle. Runoff water is created from falling precipitation initiated at high elevation. Accumulations of snowmelt and rain flow downhill, forming channels that lead directly to the ocean. However, a portion of natural runoff water flows into lakes and seeps through the ground into aquifers. The aquifers hold groundwater, which acts as a long-term reservoir for the water cycle. Thus, runoff water can contribute to the formation of additional groundwater.

Environmental Impact

• Flooding is a common consequence from massive runoff flows.

  Because runoff and groundwater exhibit different behaviors, each can cause differing environmental impacts. Surface runoff water is important because it is one of the leading causes for surface erosion and deposition. As water flows great distances over land, it can carry sediments and minerals to varying locations. Flooding is another consequence of large levels of runoff water. Research has proposed that groundwater provides lubrication to affect the movement of tectonic faults. Moreover, groundwater serves as an important reservoir for drinkable fresh water.

Significance to Humans

• Runoff water plays an important role for humans in terms of water pollution. As runoff water intersects industrial zones, many harmful chemicals and pollutants enter the water flow to be later deposited in the environment and larger bodies of water. Large amounts of excess runoff water also decrease the water table, causing droughts. On the other hand, groundwater must be protected from human activity. Extensive well pumping for agriculture can lower groundwater levels, hurting the surrounding environment. In addition, pollutants that enter underground aquifers may contaminate and decrease the amount of available drinking water.