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The Peachtree Creek watershed
Location and size
The Peachtree Creek watershed upstream of the U.S. Geological Survey (USGS) streamflow gaging station at Northside Drive (the blue circle on the map) is of vital importance to the metro Atlanta region. The watershed encompasses an area of 86.6 square miles in the northeast quadrant of the metro Atlanta area. Runoff in the watershed enters Peachtree Creek, which, in turn, flows into the Chattahoochee River a few miles to the west. The altitude at the gaging site is about 764 feet above sea level.
What is a watershed?
A watershed is an area of land that drains all the streams and rainfall to a common outlet such as the outflow of a reservoir, mouth of a bay, or any point along a stream channel. The word watershed is sometimes used interchangeably with drainage basin or catchment. Ridges and hills that separate two watersheds are called the drainage divide. The water resources of a watershed include surface water--lakes, streams, reservoirs, and wetlands--and all the underlying ground water.
A watershed is a precipitation collector
Most of the precipitation that falls within the Peachtree Creek watershed upstream of Northside Drive collects in the creek and eventually flows by the Peachtree Creek gaging site. Many factors, some listed below, determine how much of the streamflow will flow by the monitoring site. Imagine that the whole basin is covered with a big (and strong) plastic sheet. Then if it rained one inch, all of that rain would fall on the plastic, run downslope into gulleys and small creeks and then drain into Peachtree Creek. Ignoring evaporation and any other losses, then all of the approximately 1,512,000,000 gallons of water that fell (you can use our interactive rainfall calculator to find out how many gallons of water fall during a storm) as rainfall would eventually flow by the Peachtree Creek monitoring site.
Not all precipitation that falls in a watershed flows out
To picture a watershed as a plastic-covered area of land that collects precipitation is overly simplistic and not at all like a real-world watershed. A career could be built on trying to model a watershed water budget (correlating water coming into a watershed to water leaving a watershed). There are many factors that determine how much water flows in a stream (these factors are universal in nature and not particular to a single stream):
Why doesn't a stream go dry after it stops raining?
Many streams in Georgia and throughout the world typically continue to flow even after weeks without rain. The amount of water flowing is often referred to as "base flow". Water in the streams during these times comes from ground water coming from the soil along the stream bank. The ground water often flows in the direction of the land slope, toward the stream, where it seeps out of the stream bed and banks. Base flow is critical to the stream ecosystem, as well as for human uses of the stream during drought periods. The amount of base flow in a stream depends on the amount of precipitation in the watershed in the previous months, the amount of infiltration in the watershed, and the characteristics of the ground-water aquifers that may supply water to the streams.
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This URL: http://ga2.er.usgs.gov:80/peachtree/watershed.cfm
Last updated: 03/05/2013 12:58:05 PM