Statewide Flood-Frequency Analyses for Streamflow Gaging Stations in South Dakota

Executive Summary

Accurate peak-flow frequency estimates are essential for numerous engineering applications and many other purposes. The U.S. Geological Survey and the South Dakota Deptartment of Transportation have previously cooperated on many projects to improve frequency estimates for the State. Efforts typically have included both collection of peak-flow data (primarily crest-stage gages) and analyses of peak-flow data. Analyses of peak-flow data typically has been performed simply by running computer programs to implement default procedures recommended in Bulletin 17B. Various acceptable procedures are available, however, that can improve results of frequency analyses. Such procedures can include items such as approaches for handling of outliers or various approaches for extension of records.

Objective

The primary objective of this project is to perform a statewide update of peak-flow frequency estimates for applicable gaging stations in South Dakota. This effort includes compilation of information to document historic flooding in South Dakota for use in historic adjustment procedures. This effort also includes utilization of various alternative approaches, when appropriate, for performing frequency analyses.

General Approach

Peak flow characteristics for individual sites are being investigated in detail, and also will be studied in a basin-wide approach. Effects of differences in periods of record on peak-flow frequency/magnitude estimates will be thoroughly investigated. Possible errors introduced by using standard assumptions of Bulletin 17B will be considered and appropriate manual revisions would be made.

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