FAQ's about Water

A drought is a period of drier-than-normal conditions that results in water-related problems. Precipitation (either rain or snow) falls in uneven patterns across the country. The amount of precipitation at a particular location varies from year to year, but over a period of years, the average amount is fairly constant. In the deserts of the Southwest, the average precipitation is less than 3 inches per year. In contrast, the average yearly precipitation in the Northwest is more than 150 inches.

When no rain or only a very small amount of rain falls, soils can dry out and plants can die. When rainfall is less than normal for several weeks, months, or years, the flow of streams and rivers declines, water levels in lakes and reservoirs fall; also the depth to water in wells increases. If dry weather persists and water-supply problems develop, the dry period can become a drought.

Reference: Moreland, 1993, Drought: U.S. Geological Survey Water Fact Sheet, Open-File Report 93-642

The term "100-year flood," is used to describe the recurrence interval of floods. As the table below shows, the "100-year recurrence interval" means that a flood of that magnitude has a one percent chance of occurring in any given year. In other words, the chances that a river will flow as high as the 100-year flood stage this year is 1 in 100. Statistically, each year begins with the same 1-percent chance that a 100-year event will occur.

But, just because a 100-year flood happened last year doesn't mean that it won't happen this year, too. In other words, future rainfall and floods don't depend on the rainfall and floods that happened in the past. The past records are mainly used to show what kind of river flows can be expected. So, when you hear about a 100-year flood, at least you have a general idea that it does mean a BIG flood, and if you hear of a 200-year flood you know that it means one even BIGGER! As an example, in July of 1994, some places in south Georgia received more than 20 inches of rainfall in a few days -- the floods they produced were tremendous... way over the 100-year flood. At Senoia, Ga., the maximum amount of water flowing by the Line Creek gage was 2.4 times greater than the 100-year flood level.

Several types of data can be collected to assist hydrologists predict when and where floods might occur. The first is monitoring the amount of rainfall occurring on a realtime basis. Second, monitoring the rate of change in river stage on a realtime basis can help indicate the severity and immediacy of the threat. Third, knowledge about the type of storm producing the moisture, such as duration, intensity and areal extent, is valuable for determining possible severity of the flooding. And fourth, knowledge about the characteristics of a river's drainage basin, such as soil-moisture conditions, ground temperature, snowpack, topography, vegetation cover and impermeable land area, can help to predict how extensive and damaging a flood might become.

The National Weather Service collects and interprets rainfall data throughout the United States and issues flood watches and warnings as appropriate. The National Weather Service uses statistical models and flood histories to try to predict the results of expected storms. The USGS maintains a network of streamflow-gaging stations throughout the country for which the discharge and stage are monitored. Flood estimation maps are generally produced by estimating a flood with a certain recurrence interval or probability and simulating the inundation levels based on flood plain and channel characteristics. More information on floods is available from the USGS Hydrologic Information Center at http://www.nws.noaa.gov/oh/hic and from the USGS national home page at http://water.usgs.gov. For more information on real-time flood monitoring, please see USGS Fact Sheet FS-209-95, which is available on-line at http://water.usgs.gov/public/wid/FS_209-95/mason-weiger.html.

The USGS Educational Resources page provides links to online information on biology, geology, hydrology, and geography, as well as ordering information for additional materials -- many of which are available at no cost. Another excellent site is the National Biological Information Infrastructure (NBII).

To accomplish these tasks, the USGS has over 150 field offices where personnel are involved in the following activities:

Hydrologists may be concerned with finding water supplies for cities or irrigated farms, or controlling river flooding or soil erosion. Or, they may work in environmental protection, helping to prevent or clean up pollution or locate sites for safe disposal of hazardous wastes. Hydrologists use many tools to do their work, from shovels to computers and mass spectrometers, and new tools are being developed every day.

A description of hydrology and what hydrologists do can be found at http://ut.water.usgs.gov/infores/hydrology.primer.html.

The U.S. Geological Survey (USGS) recently completed an assessment of our Nation's geothermal resources. Geothermal power plants are currently operating in six states: Alaska, California, Hawaii, Idaho, Nevada, and Utah. See Fact Sheet 2008-3082 "Assessment of Moderate- and High-Temperature Geothermal Resources of the United States".

Iceland also makes great use of its geothermal resources.

How high and how fast a river will rise during a storm depends on many things. Most important, of course, is how much rain is falling. But also we have to look at other things, such as the stage of the river when the storm begins, at what the soil is like in the drainage basin where it is raining (is the soil already saturated with water from a previous storm?), and at how hard and in what parts of the basin the rain is falling. The USGS has studied these things at many places across the country for many years, and thus is often able to make predictions about if and where a flood will occur and how bad that flood will be.

With the advent of modern computer and satellite technology, the USGS can monitor the stage of many streams almost instantly. Since some streams, especially those in the normally arid Western U.S., can rise dramatically in a matter of minutes during a major storm, it is important to be able to remotely monitor how fast water is rising "in real time" in order to warn people that might be affected by a dangerous flood. Recreational users of streams, such as kayakers, also use "real-time" stream-stage data to tell them if certain streams are at the right height for kayaking. The USGS can now gather data on stream stage and even produce graphs showing stage as the rain is falling. In fact, some of these real-time data and graphics are being made available for you to use via the World Wide Web. You can access current stream conditions for your state right now.

There is no certain answer. There are 616 officially named glaciers in Alaska (see USGS Geographic Names Information System online data base), and many more unnamed glaciers. The Alaska Almanac estimates that Alaska has 100,000 glaciers -- that's a pretty good estimate.

The current El Niño will probably surpass the greatest El Niño of century, that of 1982-83. During the past 40 years, nine El Niños have affected the western coasts of North and South America. Most of them raised water temperatures along 5000 miles of coast. The weaker events raised sea temperatures only a few degrees Fahrenheit and caused mild changes in weather. But the strong ones, like the El Niño of 1982-83, left a climatic imprint that was global in extent.

El Niño recurs irregularly, from two years to a decade, and no two events are exactly alike. Before the 1982-83 El Niño event, scientists did not collect detailed information on El Niños, so information is scanty for making high-quality predictions about the effects of the current El Niño of 1997-98.

The impacts of El Niños can be devastating, as illustrated by some of the effects of the unusually strong El Niño of 1982-83:

- Drought (sometimes with associated wildfires) in many nations (particularly in the western Pacific Rim, southern and northern Africa, southern Asia, southern Europe, and parts of South and Central America);- Severe cyclones that damaged island communities in the Pacific;- Flooding over wide areas of South America, western Europe, and the Gulf Coastal states; - Severe storms in the western and northeastern United States.

NOAA is the main source of bathymetric data for the world, and here is the site you can search for their data: http://www.ngdc.noaa.gov/mgg/bathymetry/relief.html

Ground water, which is in aquifers below the surface of the Earth, is one of the Nation's most important natural resources. Ground water is the source of about 37 percent of the water that county and city water departments supply to households and businesses (public supply). It provides drinking water for more than 90 percent of the rural population who do not get their water delivered to them from a county/city water department or private water company. Even some major cities, such as San Antonio, Texas, rely solely on ground water for all their needs. About 42 percent of the water used for irrigation comes from ground water. Withdrawals of ground water are expected to rise as the population increases and available sites for surface reservoirs become more limited.

Because the red (long wavelengths) part of white light is absorbed by ice and the blue (short wavelengths) light is transmitted and scattered. The longer the path light travels in ice, the more blue it appears.

Real-time streamflow data are available from the U.S. Geological Survey for over 4200 stations throughout the United States. These data are available only through the World-Wide Web.

The American Whitewater Affiliation provides a compilation of web pages and telephone numbers where real-time streamflow and reservoir information can be obtained across the United States.

Note that direct telephone access to U.S. Geological Survey stream-gaging stations is not authorized except for official use, including those stations where National Weather Service equipment is co-located.

Access to these stations must be restricted to official use so that data are available during emergencies.

Water being drawn from a well was once precipitation that fell onto Earth's surface. It seeped into the ground and, over time, occupied the porous space in some subsurface material. Naturally, big particles that can be found in streams, such as leaf chunks, will not be seen in ground water. So, yes, big particles are filtered out. But ground water can contain other items that you can't see. Some are naturally occurring and some are human-made substances. Ground water can contain hydrogen sulfide or other naturally occurring chemicals. Ground water also may contain petroleum, organic compounds, or other chemicals introduced by humans' activities.

Contaminated ground water can occur if the well is located near land that is used for farming where certain kinds of chemicals are applied to crops, or near a gas station that has a leaking storage tank. Leakage from septic tanks and/or waste-disposal sites also can contaminate ground water. A septic tank can introduce bacteria to the water, and pesticides and fertilizers that seep into farmed soil can eventually end up in water drawn from a well. Or, a well might have been placed in land that was once used for something like a garbage or chemical dump site. In any case, it is wise to have your well water tested for contaminates.

Not directly. You cannot say that because a stream rises (doubles) from a 10-foot stage to a 20-foot stage that the amount of water flowing also doubles. Think of a cereal bowl with a rounded bottom. Pour one inch of milk in it. It doesn't take much milk to make it up to the one inch level because the bowl is least wide near the bottom. Now, pour in milk until it is two inches deep -- it takes a lot more milk than it did to fill the first inch because the bowl gets wider as you go up. The same thing happens in a stream -- the stream banks will generally be narrower at the bottom and tend to widen as you go up the bank. So, the amount of water flowing in a stream might double when the stage rises from 1 to 2 feet of stage, but then it might quadruple when it goes from 3 to 4 feet. This graphic helps to illustrate:

To find out how much water is flowing in a stream or river, USGS personnel have to go out and make a "discharge measurement." USGS uses the term "discharge" to refer to how much water is flowing, and discharge is usually expressed in "cubic feet per second" (think of a cube of water one foot on a side, and how many of those move past a point in one second). To do this, we often have to go out and stand in the creek, measure the depth and how fast the water is moving at many places across the creek. By doing this many, many times, and at many stream stages, over the years we can develop a relation between stream stage and discharge. Stream stages are not always cooperative, so its not uncommon for someone to have to go measure a stream at 2:00 in the morning during a storm, sometimes in freezing conditions! Also, the stream can be uncooperative in that it changes -- a big storm may come along and scour out bottom material of a creek, or lodge a big log sideways in the creek, or sometimes do both at the same time. These kind of changes result in changes in the relation between stage and discharge.

A more detailed explanation is available.

Saline water has some uses. In 2000, the U.S. used about 62 billion gallons per day of saline water, which was about 15 percent of all water used. But saline water can only be used for certain purposes. The main use was for thermoelectric power-plant cooling. As for the other uses, about 8 percent of water used for industrial purposes was saline, and about 43 percent of all water used for mining purposes was saline. Also, saline water can be desalinated for use as drinking water by putting it through a process to remove the salt from the water. The process costs so much that it isn't used very much right now.

First of all, plants naturally grow in and around lakes. Maybe you're asking about a lake that is being choked off by too much algae. In many cases, humans are responsible. Actually, these lakes are being fed too much food for plants! There are certain chemicals we use that are nutrients (food) to plants. At our homes we fertilize our yards with nitrogen, potassium, and phosphorus. These chemicals wash off our lawns and eventually get into the water system, such as into creeks, rivers, and lakes. Once there, algae and plants have a feast on this "food". Things used to be worse for our water bodies. Phosphorus used to be an ingredient in our laundry detergent, but this has generally been phased out.

No one knows for sure what would happen if the snow and ice in the polar regions all melted. Sea level would rise, which would flood coastal regions. Climate would be affected worldwide. Isostatic rebound would occur where ice masses were removed from continents, causing the land surface there to rise. Many scientists are trying to predict the effects of climate changes such as a general warming trend by using computer climate models. Much more research needs to be done before we can confidently predict results.