As the unprecedented floodwaters of the Red River slowly begin to subside in Grand Forks, N. Dak., crews from the U.S. Geological Survey are tracking the northward movement of the water, taking measurements to help improve forecasts of the flood for evacuations upstream.
Records of the flood flows are also vital to engineers and planners who need the information to design safe and effective future flood-control levees, reservoirs and bridges in the area.
Crucial to the understanding of the impact of the flood on upstream communities will be how much water is contributed by the Pembina River, which is the last major tributary into the Red before it enters Canada. Flow of the Pembina River at Neche, North Dak., on April 24, where the USGS maintains a streamflow gaging station, was 10,200 cubic feet per second (cfs) or 6.6 billion gallons per day (bgd) and the gage height is steady due to backwater from the Red River of the North. On April 22, the USGS crews had measured 11,800 cfs (7.6 bgd), which exceeded the previous peak record of 10,700 cfs (6.9 bgd) in 1950.
The USGS North Dakota office has been joined by USGS hydrologic monitoring crews from nine states to keep all phases of the field operation going. Specially trained crews from the USGS water resources office in Kentucky are helping North Dakota crews to install a temporary streamflow gaging station on the Red River at Pembina and will be taking additional measurements using Accoustic Doppler Current Profiler equipment. This sophisticated technology allows hydrologists to measure the velocity of water by bouncing sound waves off of suspended sediments and debris in the river, and then comparing the shift in the frequency of the echoed sound.
The echoed sound -- the Doppler shift -- is not unlike the change in emitted or reflected sound from a car passing a stationary observer; that is, higher in frequency or pitch as the car approaches the observer and lower as the car moves away. In the case of the Accoustic Doppler Current Profiler, sensitive electronic instruments detect the shift in the sound, which is directly proportional to the relative speed of the water and water-borne sediments as the water moves closer to or away from the ADCP.
ADCP discharge or volume measurements are typically made from a boat from which the equipment is suspended in the water. The boat passes across the river while scientists record river velocity and depth using the ADCP. Such measurements are particularly helpful in a flood situation such as that on the Red River because it enables hydrologists to take measurements in the river instead of from stationary points on bridges that are inundated and inaccessible. ADCP measurements are also much quicker than measurements made with standard streamflow measuring equipment.
The crest of the Red River flood is expected to reach the Canadian border on April 27 or 28, according to the river forecast center of the National Weather Service in Minneapolis, Minn. USGS crews will be taking continuous measurements between the North Dakota-South Dakota border and the Canadian border in order to provide accurate data on the volume of the river's flow for the National Weather Service to use in their forecasts of when the Red River will crest at various points along its path northward.
The current estimate of the Red's flow when it reaches the border is 135,000 cfs (87 bgd), according to the NWS river forecast center. When the crest (the highest level the river reaches) reached Grand Forks it was about 130,000 cfs (84 bgd).
The USGS, which maintains a nationwide network of streamflow gaging stations, has 100 gages in North Dakota, 50 of which are in the Red River watershed, which includes stations in Minnesota. Several gages have been inundated or damaged by the flooding and the main gage at Grand Forks was inundated during the extraordinary flood event. A temporary gage was set up on the deck of a local restaurant and is still providing critical information as the waters begin to recede by inches from the inundated city.
The USGS has made more than 225 discharge or flow measurements since the flooding began the last week in March. Crews have also been out making more than 125 inspections of gaging stations to ensure that they are operating properly.
Nationwide, 1997 has already been a year of extensive flooding. Since January 1, more than 165 USGS streamflow gaging stations have been seriously damaged or destroyed by major floods in California and Nevada, the Pacific Northwest and the Ohio River Valley. The USGS has worked quickly to replace and repair stations and to keep the information flowing from this network. Some 12-15 gages in North Dakota have also been damaged and USGS crews are working quickly to repair these gages or to install temporary gages until more permanent repairs can be made.
Through its network of 7,000 streamflow-gaging stations, which are cooperatively funded by more than 700 Federal, State and local agencies, the USGS provides essential information to the agencies responsible for flood warnings and river forecasts. Under this program, which has operated since 1887, the USGS collects streamflow information needed by federal, state and local agencies for planning and operating water-resources projects and for watershed management, in addition to flood-warning.
In recent years, the network has changed considerably with the advent and widespread use of real-time streamflow data. More than 60 percent of the stations in the network use satellite radio transmitters to broadcast data 24-hours-a-day directly to cooperators like the National Weather Service, who in turn use the information to provide river forecasts and flood warnings. The number of stations equipped with data collection platforms, which provide for the real-time data, has more than doubled in the past 10 years, even though the overall number of gages is decreasing.
General access to the real-time data is available through the World Wide Web on the Internet. Those in need of information on the height and flow of a river -- from flood forecasters to fly fishers -- can access state-by-state information through the USGS main home page at: http//www.usgs.gov. By clicking on the word "water" and then accessing "real-time streamflow," users can click on the state for which they need information and then the individual river where gaging stations are located.
In preparation for the flooding on the Red River, the USGS prepared publicly available flood tracking charts (which are also available on the Web at the North Dakota page). These colorful and easy-to-use charts can be used by local citizens and emergency response personnel to record the latest river stage and predicted flood-crest information. Instructions for using the chart and printed on the chart and are on the Web site.
The network of river-gaging stations in the Red River of the North Basin is operated by the USGS in cooperation with the U.S. Army Corps of Engineers, the National Weather Service, the North Dakota State Water Commission, the Minnesota Department of Natural Resources, the Southeast Cass Water Resources District, the Red River Joint Water Resource Board, and the Red River Watershed Management Board.
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The chart and the records of previous peaks and hydrographs provide interesting graphics that can be easily downloaded. For interviews and further information on the current flooding, please call Gregg Wiche or Russ Harkness, USGS, Bismarck, N.Dak., 701-250-4601.)