Methods for estimating annual exceedance-probability discharges and largest recorded floods for unregulated streams in rural Missouri.

PDFTech Report2014\uc2\ubf5165Rural areasStreamsFloodsSediment dischargeRegression analysisGeographic information systemsStream gagesPeak dischargeDrainage basinsMissouriGeological Survey (U.S.)Southard, Rodney E.Veilleux, Andrea G.Geological Survey (U.S.)Missouri. Dept. of TransportationUnited States. Federal Emergency Management AgencyUS Transportation CollectionRegression analysis techniques were used to develop aset of equations for rural ungaged stream sites for estimatingdischarges with 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percentannual exceedance probabilities, which are equivalent toannual 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 characteristicswere computed for use in preliminary statewide and regionalregression analyses. Annual exceedance-probability dischargeestimates were computed for 278 streamgages by using theexpected moments algorithm to fit a log-Pearson Type IIIdistribution to the logarithms of annual peak discharges foreach streamgage using annual peak-discharge data from wateryear 1844 to 2012. Low-outlier and historic information wereincorporated into the annual exceedance-probability analyses, and a generalized multiple Grubbs-Beck test was used todetect potentially influential low floods. Annual peak flowsless than a minimum recordable discharge at a streamgagewere incorporated into the at-site station analyses