Water Questions & Answers

Measuring Water

• What water data does the USGS gather?
• What does river stage mean?
• Does stage tell you how much water is flowing?
• A "100-year flood" two years in a row. How can that be?
• Is measuring water in a well like measuring a stream?
• Why do water levels in wells rise and fall?

Floods, droughts, glaciers:

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• Droughts Q&A
• Glaciers Q&A

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Water Questions & Answers
Why do water levels in wells rise and fall?

Hydrograph of a well in Georgia that is heavily used for irrigation. Water levels rise and fall due to pumping characteristics and precipitation.

Water levels in wells are constantly changing both in the short term and over the long term. Some wells even have a seasonal change. In the short term, water levels can be lowered just by pumping water out of the well for use. Also, a well may be pumped so much as to cause the water level in nearby wells to be lowered, too. In some places people have withdrawn water faster than water replenishes the aquifer, and the wells have stopped producing water. It all depends on how fast the aquifer that the well uses is resaturated with water from the surface or from the area surrounding it (recharge). The characteristics of the rock that make up the aquifer come into play here, especially how permeable and porous the aquifer is.

Sometimes this is a long-term problem occurring over a very large area. If the underground-rock characteristics mean that it takes a long time for precipitation to replenish the aquifer, and if wells are pumping at a significant enough rate, then whole group of wells may stop producing usable water. Users will have to wait until the aquifer becomes more saturated again before turning back on the pumps. Also, an aquifer can only contain water if there is water coming into it, usually from rainwater seeping down from the surface. In a severe drought water levels in wells can significantly decline.