The 2-, 5-, 10-, 25-, 50-, and 100-year floods are determined for gaged sites on 120 selected, small drainage basins in South Dakota. These estimates are from the frequency curves defined from the streamflow records. Short-term records for 66 sites were extended on the basis of long-term climatic records and a rainfall-runoff model. These frequency curves may provide the best estimates of floods at these gaged sites. Analyses of flood-frequency information from these gaged sites have been the basis for techniques (published previously) used in estimating flood magnitude and frequency at ungaged sites in South Dakota.
This report supplements flood-frequency information published earlier. It presents: Annual peak discharges colected during a 25-year period at 124 crest-stage partial-record stations; maximum observed and unit discharges determined for 124 crest-stage and 120 continuous-record gaging stations; updated flood-frequency curves for 120 crest-stage gages; a documentation of analytical procedures used; and a summary of the small-streams flood-peak data collection program in the State from 1955 to 1981. Maximum flood peaks determined at 244 partial- and continuous-record gaging stations and at 52 miscellaneous sites are compared with regional flood relationships.
