The probable magnitude of floods of any recurrence interval between 1.1 and 50 years for any stream in the Great Basin can be determined by methods presented in this report.
The Great Basin comprises nearly all of Nevada, western Utah, eastern California, and parts of Idaho, Oregon, and Wyoming. The physiography of the basin is a series of mountain ranges and desert valleys, which trend in a north-south direction. Extreme variations in climate from arid to humid are attributed to the mountains, which, in general, are at right angles to the prevailing westerly winds. The area is subject to cloudburst floods and mud-rock flows, and this situation often results in high rates of runoff and heavy erosion from small drainage basins. The greater part of the basin is desert, and because of the paucity of flood data, the flood characteristics are poorly defined.
Two sets of curves are provided for estimating the magnitude and frequency of floods: (1) curves that represent the ratio of a flood of any frequency to the mean annual flood, and (2) curves that relate the mean annual flood to the size of the drainage basin and, where significant, to the mean altitude of the basin. Using these curves, a flood of a selected frequency can be determined for any site within the range of the base data. Separate 50-year flood graphs are shown for most of the larger rivers that are affected by regulation or diversion.
The report also contains station descriptions and lists of peak discharges for 364 gaging stations at which flood records have been collected for 5 or more years.
