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Surface runoff often occurs because impervious areas (such as roofs and pavement) do not allow water to soak into the ground. Furthermore, runoff can occur either through natural or human-made processes. [5] Surface runoff is a major component of the water cycle. It is the primary agent of soil erosion by water.
Surface runoff (also known as overland flow or terrestrial runoff) is the unconfined flow of water over the ground surface, in contrast to channel runoff (or stream flow). It occurs when excess rainwater , stormwater , meltwater , or other sources, can no longer sufficiently rapidly infiltrate in the soil .
Organisms which cause acid mine drainage can thrive in waters with pH very close to zero. Negative pH [11] occurs when water evaporates from already acidic pools thereby increasing the concentration of hydrogen ions. About half of the coal mine discharges in Pennsylvania have pH under 5. [12]
The runoff from the land flows into streams and rivers and discharges into the ocean, which completes the global cycle. [26] The water cycle is a key part of Earth's energy cycle through the evaporative cooling at the surface which provides latent heat to the atmosphere, as atmospheric systems play a primary role in moving heat upward.
Because of fertilizer and organic waste that urban runoff often carries, eutrophication often occurs in waterways affected by this type of runoff. After heavy rains, organic matter in the waterway is relatively high compared with natural levels, spurring growth of algae blooms that soon consume most of the oxygen .
In these environments, surface runoff is usually generated by a failure of rainfall to infiltrate into the ground quickly enough (this runoff is termed infiltration excess overland flow). This is more likely to occur on bare soil, with low infiltration capacity. As runoff flows downslope, it may run-on to ground with higher infiltration ...
Marine-life experts say the toxic runoff can have both acute, immediate impacts on the fish and other aquatic life living in the bay, along with long-term impacts like widespread die-offs.
The quickest response times between rainfall and streamflow occur in urbanized areas where yard drains, street gutters, and storm sewers collect overland flow and route it to streams straightaway. Runoff velocities in storm sewer pipes can reach 10 to 15 feet per second. [2]