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|  | Pine River Watershed Alliance: “What is a watershed?”When looking at the location of rivers and the amount of streamflow in rivers, the key concept is the river's "watershed". What is a watershed? “This is a frequently asked question” said Ron Meyer, chairman of the Pine River Watershed Alliance (PRWA), “and some people don’t think that they live in a watershed.” But, if you are standing on ground right now, just look down. You're standing, and everyone is standing, in a watershed. A watershed is the area of land where all of the water that falls in it and drains off of it goes into the same place. Watersheds can be as small as a footprint or large enough to encompass all the land that drains water into rivers that drain into the Mississippi River, where it enters the Gulf of Mexico. 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 watershed consists of surface water--lakes, streams, reservoirs, and wetlands--and all the underlying ground water. Larger watersheds contain many smaller watersheds. “In the case of the 500,000 plus acres of the Pine River Watershed, there are five sub watershed”, said Meyer. They are the Upper Pine River in the Backus area, the South Fork that starts along the east edge of the Foothills State Forest west of the city of Pine River, the Lower Pine River that encompasses most of the Whitefish Chain of Lakes, the Daggett Brook sub watershed that includes the Outing and Fifty Lakes Areas, and the Little Pine River that takes in the Emily area and east to the Aitkin County line. All of the water from these sub watersheds flows into the Mississippi River south of Cross Lake. It all depends on the outflow point; all of the land that drains water to the outflow point is the watershed for that outflow location. Watersheds are important because the streamflow and the water quality of a river are affected by things, human-induced or not, happening in the land area "above" the river-outflow point. A watershed is a precipitation collector Most of the precipitation that falls within the drainage area of a stream's monitoring site collects in the stream and eventually flows by the monitoring 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 main stream. Ignoring evaporation and any other losses, and using a 1-square mile example watershed, then all of the approximately 17,378,560 gallons of water that fell as rainfall would eventually flow by the watershed-outflow point. Meyer pointed out that “the Pine River Watershed is about 783 square miles. So you can multiply that 17-million gallons of water in just one inch of rain by 783 to get some perspective of the amount of water that we are concerned about here, not to mention lakes and wetlands that are standing in the watershed.” 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 realworld 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): • Precipitation: The greatest factor controlling streamflow, by far, is the amount of precipitiation that falls in the watershed as rain or snow. However, not all precipitation that falls in a watershed flows out, and a stream will often continue to flow where there is no direct runoff from recent precipitation. • Infiltration: When rain falls on dry ground, some of the water soaks in, or infiltrates the soil. Some water that infiltrates will remain in the shallow soil layer, where it will gradually move downhill, through the soil, and eventually enters the stream by seepage into the stream bank. Some of the water may infiltrate much deeper, recharging ground-water aquifers. Water may travel long distances or remain in storage for long periods before returning to the surface. • Evaporation: Water from rainfall returns to the atmosphere largely through evaporation. The amount of evaporation depends on temperature, solar radiation, wind, atmospheric pressure, and other factors. • Transpiration: The root systems of plants absorb water from the surrounding soil in various amounts. Most of this water moves through the plant and escapes into the atmosphere through the leaves. Transpiration is controlled by the same factors as evaporation, and by the characteristics and density of the vegetation. Vegetation slows runoff and allows water to seep into the ground. • Storage: Reservoirs store water and increase the amount of water that evaporates and infiltrates. The storage and release of water in reservoirs can have a significant effect on the streamflow patterns of the river below the dam. • Water use by people: Uses of a stream might range from a few homeowners and businesses pumping small amounts of water to irrigate their lawns to large amounts of water withdrawals for irrigation, industries, mining, and to supply populations with drinking water. “It is a lot easier to connect with water and get involved if you live on a lake or stream”, said Meyer. “But we all are affected by what happens to the water in our watershed and even though it is hard to visualize or connect with the idea, we need all residents to get involved in insuring their water is properly cared for.” The Alliance is always interested in more people getting involved or attending their meetings. Please contact Ron Meyer at prwatershed@crosslake.net or call him at Voicemail: (218) 692- 1020 for more information. Information for this article was obtained from the U. S. Geological Survey, Department of the Interior/USGS http://ga.water.usgs.gov/edu/watershed.html. The USGS home page is http://www.usgs.gov. | |||||||||||||||||||||||||||||||||||
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