Flood hazard information is needed for small streams as well as for large ones. This report explains methods of defining the magnitude and frequency of floods in Nebraska on uncontrolled and unregulated streams which have about 300 square miles or less of drainage area contributing to surface runoff. Composite frequency curves defined for two flood regions express a ratio of floods with recurrence intervals ranging from 1.1 to 25 years to the mean annual flood. Curves for 10 hydrologic areas were defined to show the relation of the mean annual flood to the contributing drainage area. A flood-frequency curve can be drawn from these two sets of curves for any site in the State within the range of drainage area and recurrence interval that is defined by the base data and not materially affected by the works of man. The two sets of curves are based on all available pertinent data from records of 5 or more years' duration. This report includes a tabulation of maximum flood peaks at gaging stations used and at a number of miscellaneous sites which have less than 300 square miles of contributing drainage area. Geological Survey, under the direction of Floyd F. LeFever, district engineer, Surface Water Branch, in cooperation with the Nebraska Department of Roads. Financial assistance in the preparation of the report was given by the Bureau of Public Roads. DESCRIPTION OF AREA PHYSIOGRAPHY Nebraska has an expansive, gently rolling to rough topography, broken in places by low hills, a few isolated buttes, mesas, ravines, and several relatively shallow, major streams which flow in an easterly direction. CLIMATE The climate of Nebraska is typical of large interior continental areas in the middle latitude; it is characterized by light average annual precipitation, a great range of precipitation from season to season and year to year, and frequent and abrupt changes in temperature and other weather conditions. The average annual rainfall shows a gradual progressive increase from 14 inches in the extreme western part of the State to 34

The characteristics of flow in a reach of alluvial channels on the Elkhorn River were observed. The variations in channel width, bed elevations, bed configurations, and roughness coefficients are described and related to certain hydraulic parameters previously defined in laboratory and field studies of flow in alluvial channels. 1000 2000 FEET FIGXTBE 1. Map showing site of investigation.

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