Regression analysis techniques were used to develop a set
of equations for rural ungaged stream sites for estimating discharges with 50-,
20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities,
which are equivalent to annual flood-frequency recurrence intervals of 2, 5,
10, 25, 50, 100, 200, and 500 years, respectively. Basin and climatic
characteristics were computed using geographic information software and digital
geospatial data. A total of 35 characteristics were computed for use in
preliminary statewide and regional regression analyses. Annual
exceedance-probability discharge estimates were computed for 278 streamgages by
using the expected moments algorithm to fit a log-Pearson Type III distribution
to the logarithms of annual peak discharges for each streamgage using annual
peak-discharge data from water year 1844 to 2012. Low-outlier and historic
information were incorporated into the annual exceedance-probability analyses,
and a generalized multiple Grubbs-Beck test was used to detect potentially
influential low floods. Annual peak flows less than a minimum recordable
discharge at a streamgage were incorporated into the at-site station analyses. Annual
peak data from streamgages were used to qualitatively assess the largest floods
recorded at streamgages in Missouri since the 1915 water year.
Published: September 2014
Report number: U.S. Geological Survey Scientific Investigations Report 2014-5165
Project number: TR201120
Author(s): Rodney E. Southard and Andrea G. Veilleux
Performing organization(s): U.S. Geological Survey; prepared in cooperation with the Missouri Department of
Transportation and Federal Emergency Management Agency
