Why is runoff important to the water cycle

For example, in during a major storm at Peachtree Creek in Atlanta, Georgia, the amount of water that flowed in the river in one day was 7 percent of all the streamflow for the year. That part of the precipitation, snow melt, or irrigation water that appears in uncontrolled not regulated by a dam upstream surface streams, rivers, drains or sewers.

Runoff may be classified according to speed of appearance after rainfall or melting snow as direct runoff or base runoff, and according to source as surface runoff, storm interflow, or groundwater runoff.

The depth to which a watershed drainage area would be covered if all of the runoff for a given period of time were uniformly distributed over it. A significant portion of rainfall in forested watersheds is absorbed into soils infiltration , is stored as groundwater, and is slowly discharged to streams through seeps and springs. Flooding is less significant in these more natural conditions because some of the runoff during a storm is absorbed into the ground, thus lessening the amount of runoff into a stream during the storm.

As watersheds are urbanized, much of the vegetation is replaced by impervious surfaces , thus reducing the area where infiltration to groundwater can occur. Thus, more stormwater runoff occurs—runoff that must be collected by extensive drainage systems that combine curbs, storm sewers as shown in this picture , and ditches to carry stormwater runoff directly to streams. More simply, in a developed watershed, much more water arrives into a stream much more quickly, resulting in an increased likelihood of more frequent and more severe flooding.

What if the street you live on had only a curb built around it, with no stormwater intake such as the one pictured here. Any low points in your street would collect water when it rained.

And if your street was surrounded by houses with yards sloping uphill, then all the runoff from those yards and driveways would collect in a lake at the bottom of the street.

Credit: Robert Lawton. A storm sewer intake such as the one in this picture is a common site on almost all streets. Rainfall runoff, and sometimes small kids' toys left out in the rain, are collected by these drains and the water is delivered via the street curb or drainage ditch alongside the street to the storm-sewer drain to pipes that help to move runoff to nearby creeks and streams. Drainage ditches to carry stormwater runoff to storage ponds are often built to hold runoff and collect excess sediment in order to keep it out of streams.

Runoff from agricultural land and even our own yards can carry excess nutrients, such as nitrogen and phosphorus into streams, lakes, and groundwater supplies. These excess nutrients have the potential to degrade water quality.

As it flows over the land surface, stormwater picks up potential pollutants that may include sediment, nutrients from lawn fertilizers , bacteria from animal and human waste , pesticides from lawn and garden chemicals , metals from rooftops and roadways , and petroleum by-products from leaking vehicles.

Pollution originating over a large land area without a single point of origin and generally carried by stormwater is considered non-point pollution. Header link November 3, Header link May 15, Water Education Foundation. Aquapedia background September 12, Runoff is a combination of surface runoff, interflow and baseflow: Surface Runoff : Surface runoff comes from overland flow and saturation excess overland flow. Overland flow is from urban sources like roofs or pavement, while saturation excess overland flow is from precipitation or melted snow that simply could not be absorbed into the ground.

Surface runoff from both of these sources is driven downhill by gravity. Storm Interflow : Interflow usually comes about after a large amount of precipitation.

Referring Pages. Share this page. Reference Terms. Runoff that occurs on surfaces before reaching a channel is also called overland flow. A land area which produces runoff draining to a common point is called a watershed. Related Stories. Now, using data from the fire, researchers have created an experimental And researchers