2001 floods in the Red River of the North basin in eastern North Dakota and western Minnesota

The Red River of the North is a complex river system in the north-central plains of the United States. The river continues to impact the people and property within its basin. During the spring of 2001, major flooding occurred for the second time in four years on the Red River of the North and its many tributaries in eastern North Dakota and western Minnesota. Unlike the 1997 floods, which were the result of record-high snowpacks region-wide and a late spring blizzard, the 2001 floods were the result of above-average soil moistures in some areas of the basin, rapid melting of above-average snowpacks in the upper basin, and heavy rainfall that swept across the region on April 7, 2001.

 The U.S. Geological Survey (USGS), one of the principal Federal agencies responsible for the collection and interpretation of water-resources data, works with other Federal, State, and local agencies to ensure that accurate and timely data are available for making decisions regarding the public's welfare. This report presents preliminary water-resources 2001 flood data that were obtained from selected streamflow-gaging stations located in the Red River of the North Basin.

Flooding in eastern North Dakota and western Minnesota usually is caused by spring snowmelt, and the severity of the flooding is affected by (1) substantial precipitation in the fall that produces high levels of soil moisture, (2) above-normal snowfall in the winter, (3) moist, frozen ground that prohibits infiltration of moisture, (4) a late spring thaw, (5) above-normal precipitation during spring thaw, and (6) ice jams (temporary dams of ice) on rivers and streams.

Stream stages (height of water in a stream above an arbitrarily established datum) and discharges measured by USGS personnel at streamflow-gaging stations are used to define a unique relation between stage and discharge. This relation, commonly called a rating curve, may not be well defined at extreme high discharges because these discharges are rare events of short duration and have unstable conditions that often make measurement extremely difficult. Therefore, estimates for some peak discharges need to be extrapolated from rating curves extended to known peak stages. The peak discharges are used to determine the probability, often expressed in recurrence intervals, that a given discharge will be exceeded in the future. For example, a flood that has a 1-percent chance of exceedance in any given year would, on the long-term average, be expected to occur only about once a century; therefore, the flood would be termed a "100-year flood." However, the chance of such a flood occurring in any given year is 1 percent. Thus, a 100-year flood can occur in successive years at the same location. In some instances, recurrence interval estimates can be based on periods of regulated flow or made with historic adjustments when historic data are available.

Historical peak stages and peak discharges and the 2001 peak stages, peak discharges, and recurrence intervals are shown in table 1. The streamflow-gaging stations are listed in downstream order by station number, and station locations are shown in figure 1. Revisions to the 2001 peak stages and peak discharges given in this preliminary report may occur as site surveys are completed and additional field data are reviewed in the upcoming months.