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Frequently Asked Questions

  1. How do I obtain streamflow data?
  2. What is stage and how does it relate to depth or discharge?
  3. During the winter when streams are ice covered, the stream discharge for my river is not shown on the real-time streamflow page. Why not?
  4. How are data collected at U.S. Geological Survey gaging stations transferred automatically to the USGS web site?
  5. How are floods predicted?
  6. Why is Devils Lake rising?
  7. What is the current level of Devils Lake and how do I find out more about Devils Lake?
  8. Why does the Red River flow north?
  9. What does a hydrologist do?
  10. Are USGS reports copyrighted?
  11. How can I find photographs by the USGS for reproduction?
  12. We had a "100-year flood" two years in a row. How can that be?
  13. What does the term "stream stage" mean?
  14. Does "stage" tell you how much water is flowing in a stream?
  15. Why do some real-time stream-gaging stations experience equipment problems for extended periods of time?
  16. Why are updated real-time stream-gaging data available only every 4 hours?

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Alternative Text-based List of FAQ's

1. How do I obtain streamflow data?

These data can be obtained from the USGS web site at  Links are provided for each of the gaging stations in North Dakota.  If you have problems accessing these data, e-mail or call or write the North Dakota Water Science Center Data Section Chief:

Steve Robinson
U.S. Geological Survey
821 E. Interstate Avenue
Bismarck, ND 58503-1199
Phone: (701) 250-7404
Fax: (701) 250-7492

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2. What is stage and how does it relate to depth or discharge?

Stage is the elevation of the water surface of a river, stream, or lake and is measured from an arbitrary datum that usually is below the elevation of the lowest expected stage or near the stream bottom. Therefore, stage may be close to the depth of water at the gage, depending on where the arbitrary "zero" of the datum is placed. Mean sea level elevation of the water surface is calculated by adding the recorded stage at the gage to the elevation of the gage datum, where it has been determined.

A stage-discharge relation, which is used continuously to compute discharge, in cubic feet per second, from stage (gage height), is developed for each station. The relation is developed with time by correlating stage and discharge measurements made during a range of flows. The relation varies from station to station and from time to time and it can shift with shifting sediment in the channel, growth and decay of weeds in the water, or ice cover in the winter. If a logjam or icejam exists in the channel, the relation may not apply at all.

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3. During the winter when streams are ice covered, the stream discharge for my river is not shown on the real-time streamflow page. Why not?

Because many North Dakota rivers and lakes are frozen during the winter,  the discharges computed from the stage-discharge relation (see Question 2) are meaningless. Therefore, discharges are not shown on our web site during the ice-affected period because the discharges are not correct and would be misleading. After the ice goes out in the spring, current discharge is again shown for these rivers and lakes.

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4. How are data collected at USGS gaging stations transferred automatically to the USGS web site?

The gaging stations for which data appear on the Current Streamflow Conditions section of our web site have satellite telemetry that basically works like this--An electronic data logger, using a 12-volt battery supply, monitors and records gage heights at selected intervals (usually 15 minutes). The data are periodically transmitted to a satellite in geo-stationary orbit over the equator. The transmitter is called a GOES radio transmitter, and USGS stations typically transmit data every 4 hours. The data are relayed via the satellite to a groundstation in Maryland and then from Maryland via satellite to a USGS groundstation in Denver, Colorado.  The data are transmitted via landline to our computer system. USGS software decodes the data, which often (but not always) arrive in binary format, and puts the data in a format that our hydrologic-data processing software (ADAPS) can recognize. The gage-height data are stored and manipulated to provide streamflow in cubic feet per second.  USGS website software continuously accesses the various data files (site information, gage height, and discharge) and portrays the information graphically. Most of the data-logging systems use 12-volt power from a wet-cell battery with a solar panel recharging system. Data also can be transmitted via cellular and FM frequencies, but both require direct line of sight to a repeater.

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5. How are floods predicted?

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

There are two basic kinds of floods, flash floods and the more widespread river flooding. Flash floods generally cause greater loss of life, and river floods generally cause greater loss of property. A flash flood occurs when runoff from excessive rainfall causes a rapid rise in the stage of a stream or fills a normally dry channel. Flash floods are more common in areas that have a dry climate and rocky terrain because the lack of soil or vegetation allows torrential rains (typically from summer thunderstorms) to flow overland rather than infiltrate into the ground. River floods generally are more common for larger rivers in areas that have a wet climate and occur when excessive runoff from longer-lasting rainstorms (such as from a cold front) and sometimes from melting snow causes a slow water-level rise and occur over a large area. Floods also can be caused by ice jams on a river or high tides. Most floods can be linked to a storm of some kind.

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 predict the possible results of expected storms. 

The USGS maintains a network of streamflow-gaging stations throughout the country for which discharge and stage are monitored. Flood estimation maps generally are produced by estimating a flood with a certain recurrence interval or probability and simulating the inundation levels on the basis of flood-plain and channel characteristics.

More information on floods is available from the National Weather Service Hydrologic Information Center at and from the USGS national home page at  For more information on real-time flood monitoring, please see USGS Fact Sheet FS-209-95, which is available on-line at

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6. Why is Devils Lake rising?

According to the U.S. Geological Survey Fact Sheet, Climatology and Potential Effects of an Emergency Outlet, Devils Lake Basin, North Dakota:

Since the end of glaciation about 10,000 years ago, Devils Lake has fluctuated between spilling and being dry. Research by the North Dakota Geological Survey indicates Devils Lake has overflowed into the Sheyenne River at least twice during the past 4,000 years and has spilled into the Stump Lakes several times (Bluemle, 1991; Murphy and others, 1997). John Bluemle, North Dakota State Geologist, concluded the natural condition for Devils Lake is either rising or falling, and the lake should not be expected to remain at any elevation for a long period of time.

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7. What is the current level of Devils Lake and how do I find out more about Devils Lake?

Current gage height data for Devils Lake are available through the online National Water Information System (NWISWeb) at URL The number of days displayed can be selected by changing the value in the text box labeled Days and clicking on the Get Data button. Data can be displayed for 1 to 31 days using this method.

To display data for more than 31 days, go to the blue bar with white text saying Available data for this site. Click on the down arrow to the right of the white textbox with the text Real-time in it. Choose Recent Daily and then, depending on your Internet browser, click on the Go button. Below the blue bar, you will have three boxes labeled, Available Parameters, Output Format, and Days. The number of days can be changed to any whole number 1 through 730. Click on the Get Data button to access the data.

Additional information for Devils Lake is summarized at This web page has links to the data in NWISWeb as well as links to the following:

  • Devils Lake elevation, area, and capacity table;
  • Devils Lake elevation period of record graph;
  • Devils Lake elevation graph for the previous 10 years;
  • Devils Lake period of record text file;
  • Morrison Lake (a lake in the Devils Lake Basin) period of record text file;
  • Dry Lake (a lake in the Devils Lake Basin) period of record text file; and
  • Lake Alice-Irvine Channel (in the Devils Lake Basin) period of record text file.

The summary page also can be accessed by going to the main web page, and then clicking on and then clicking on Devils Lake Basin.

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8. Why does the Red River flow north?

Lake Agassiz, a lake formed by melting glaciers, covered much of what is today western Minnesota, eastern North Dakota, southern Manitoba, and southwestern Ontario from about 12,500 years ago to about 7,500 years ago. Lake Agassiz virtually disappeared, leaving a few remnants like Minnesota's Upper and Lower Red Lakes and Lake of the Woods and Canada's Lake Winnipeg, Lake Manitoba, and Lake Winnipegosis.  Lake Agassiz also left a fertile, flat plain that drains to the north, ultimately to Hudson Bay. The Red River flows north through this plain to Lake Winnipeg because, despite the plain being very flat, a difference in elevation exists along the route of the river, making the line between southeastern North Dakota and Lake Winnipeg slightly downhill. At the confluence of the Bois de Sioux and Otter Tail Rivers near Wahpeton, North Dakota, where the Red River begins, the elevation is 943 feet above mean sea level. The elevation of Lake Winnipeg is 714 feet above mean sea level.  CLICK HERE TO SEE A MAP OF THE ELEVATION CHANGE.

This web site has a page at with links to U.S. Geological Survey information about the Red River and its basin, including publications, hydrographs, and pictures.

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9. What does a hydrologist do?

Hydrologists study all aspects of water and its relation to geography, geology, biology, and chemistry. Of great interest to many hydrologists is finding new water resources and keeping those water resources viable for current and future use.  Interest also is focused on how to keep our streams, lakes, reservoirs, and subsurface water supplies from being polluted and on how to clean up the water that already has been contaminated. As scientists, hydrologists are very interested in how water moves through the hydrologic cycle and where in the cycle water is most vulnerable to degradation. Hydrologists use many tools, from buckets to mass spectrometers, to do their work, and new tools are being developed every day. Computers undoubtedly are the most used tool. A description of hydrology and what hydrologists do can be found at

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