GEOLOGY

Detailed explanation-1: -Runoff is a major source of water pollution. As the water runs along a surface, it picks up litter, petroleum, chemicals, fertilizers, and other toxic substances. From California to New Jersey, beaches in the U.S. are regularly closed after heavy rainfall because of runoff that includes sewage and medical waste.

Detailed explanation-2: -Earlier sections of this lesson presented the following runoff examples: (1) snowmelt in mountains, (2) torrential rains, (3) agricultural practices, and (4) construction work.

Detailed explanation-3: -Runoff can be described as the part of the water cycle that flows over land as surface water instead of being absorbed into groundwater or evaporating. Runoff is that part of the precipitation, snow melt, or irrigation water that appears in uncontrolled surface streams, rivers, drains, or sewers.

Detailed explanation-4: -Surface runoff is defined as precipitation (rain, snow, sleet, or hail) that reaches a surface stream without ever passing below the soil surface.