Flooding in the Southern Midwestern United States, April–May 2017

Home , Bryant Creek, Four Corners, Midwestern United States

Open-File Report 2018–1004

U.S. Department of the Interior U.S. Geological Survey Above: Rapid-deployment gage installation, Gasconade River near Rich Fountain, Mo., May 1, 2017. Photograph by Larry Buschmann, U.S. Geological Survey (USGS).

Front cover. Top center: Floodwater at Current River at Doniphan, Mo., May 1, 2017. Photograph by Shannon Kelly, USGS. Upper left: USGS hydrologic technician inspects gage at Big River at Byrnesville, Mo., May 1, 2017. Photograph by Aaron Walsh, USGS. Upper right: USGS hydrologic technician inspects gage platform at St. Francis River near Patterson, Mo., peak flood, April 30, 2017. Photograph by Josh Keele, USGS. Bottom center: USGS hydrologic technician wading from gage at Black River near Poplar Bluff, Mo., May 1, 2017. Photograph by Jarret Ellis, USGS. Flooding in the Southern Midwestern United States, April–May 2017

By David C. Heimann, Robert R. Holmes, Jr., and Thomas E. Harris

Open-File Report 2018–1004

U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior RYAN K. ZINKE, Secretary U.S. Geological Survey William H. Werkheiser, Deputy Director exercising the authority of the Director

U.S. Geological Survey, Reston, Virginia: 2018

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Suggested citation: Heimann, D.C., Holmes, R.R., Jr., and Harris, T.E., 2018, Flooding in the southern Midwestern United States, April–May 2017: U.S. Geological Survey Open-File Report 2018–1004, 36 p., https://doi.org/10.3133/ofr20181004.

ISSN 2331-1258 (online) iii

Contents

Abstract...... 1 Introduction...... 1 April–May 2017 Flooding—Antecedent Conditions, Chronology, and Magnitude...... 1 Antecedent Streamflow and Weather Conditions for the 2017 Southern Midwest Flooding...... 3 Flood Chronology...... 3 Magnitude of April–May 2017 Flooding...... 16 April–May 2017 Flooding—Comparison with Historic Floods...... 17 April–May 2017 Flooding—Annual Exceedance Probability...... 17 Temporal Changes in Annual Peak Streamflows...... 18 Summary...... 31 References Cited...... 31 Glossary...... 35

Figures

1. Map showing the Midwestern United States and flood study area associated with the April–May 2017 flood...... 2 2. Map showing location of selected U.S. Geological Survey streamgages and aerial video documentation locations within the designated flood study area...... 8 3. Maps showing streamflow conditions at selected U.S. Geological Survey streamgages in the study area before the April–May 2017 flooding including January, February, March, and April of 2017...... 9 4. Maps showing monthly precipitation conditions in the United States for January–April 2017, as a percent of normal...... 11 5. Map showing the 500 millibar height contours for April 29, 2017, across the continental United States...... 12 6. Maps showing daily surface weather maps at 7:00 AM Eastern Standard Time from April 29 to 30, 2017...... 13 7. Map showing cumulative rainfall totals over the southern Midwest United States during April 28–30, 2017...... 14 8. Streamflow hydrographs and precipitation totals and distributions for selected U.S. Geological Survey streamgages and precipitation stations within the study area...... 15 9. Graph showing annual number of peak-of-record streamflows and number of U.S. Geological Survey streamgages in the study area with peak streamflow record...... 17 10. Map showing the spatial distribution of the magnitude of annual exceedance probabilities of peak streamflows at 59 U.S. Geological Survey streamgages for the April–May 2017 flood...... 26 11. Maps showing percentage changes in median annual peak streamflow values for selected U.S. Geological Survey streamgages for 1930–2017, 1956–2017, 1975–2017, and 1989–2017...... 27 12. Maps showing the percentage change in the median annual precipitation by climate division within the study area for 1930–2016, 1956–2016, 1975–2016, and 1989–2016...... 29 iv

13. Graphs showing change in frequency of daily high intensity (greater than 2–3 in.) precipitation from the long-term (1900–2014) average, by state...... 30

Tables

1. Peak streamflow and stage data at selected U.S. Geological Survey streamgages in the flood study area for the flood of April–May 2017...... 4 2. Date, times, and locations of aerial video footage documenting the effects of the April–May 2017 flood at selected locations in south-central Missouri...... 16 3. Estimated annual exceedance probability of the 2017 flood peaks and weighted peak streamflow estimates for selected flood quantiles at 59 U.S. Geological Survey streamgages included in this study...... 21

Films

1. Daily distribution of streamflow conditions in the study area, April 27–May 10, 2017...... 3 2. Spring Creek at Highway AP bridge near Willow Springs, Missouri, April 30, 2017, at 10:30 a.m...... 16 3. North Fork River and Spring Creek at Highway 14, Douglas County, Missouri, April 30, 2017, at 12:09 p.m...... 16 4. North Fork River at Highway CC, Ozark County, Missouri, April 30, 2017, at 12:37 p.m...... 16 5. Bryant Creek at Highway 181, Ozark County, Missouri, April 30, 2017, at 13:06...... 16 6. North Fork River at Highway PP near Tecumseh, Missouri, Ozark County, April 30, 2017, at 13:40...... 16 7. Dry Creek at Highway AP near Willow Springs, Missouri, April 30, 2017, at 15:29...... 16 v

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain Length foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) Area square mile (mi2) 259.0 hectare (ha) square mile (mi2) 2.590 square kilometer (km2) Flow rate cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s) Pressure millibar (mbar) 0.1 kilopascal (kPa)

Datum

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Abbreviations

AEP annual exceedance probability EMA expected moments algorithm FEMA Federal Emergency Management Agency ID identifier RRE regional regression equations USGS U.S. Geological Survey Above: Peak flood at Saint Francis River near Saco, Mo., April 30, 2017. Photograph by Chris Rowden, USGS. Flooding in the Southern Midwestern United States, April–May 2017

By David C. Heimann, Robert R. Holmes, Jr., and Thomas E. Harris

Abstract [Missouri Department of Public Safety, State Emergency Management Agency, 2017], 18 in Oklahoma [Federal Excessive rainfall resulted in flooding on numerous rivers Emergency Management Agency (FEMA), 2017b], and 13 throughout the southern Midwestern United States (southern in Arkansas [FEMA, 2017a]) were declared Federal disaster Midwest) in late April and early May of 2017. The heaviest areas. In Missouri alone, the flooding resulted in destruc- rainfall, between April 28 and 30, resulted in extensive flood- tion or damage to more than 1,200 homes and caused at least ing from eastern Oklahoma to southern Indiana including parts $58 million in damage to roads, bridges, and other public of Missouri, Arkansas, and Illinois. infrastructure (Office of Missouri Governor, 2017). Peak-of-record streamflows were set at 21 U.S. Geologi- The purpose of this report is to document the flood peaks cal Survey (USGS) streamgages in the southern Midwest (stage and streamflow) of selected U.S. Geological Survey during the resulting April–May 2017 flooding and each (USGS) streamgages within the southern Midwest that were of the five States included in the study area had at least affected by the April–May 2017 floods, placing them in one streamgage with a peak of record during the flood. The hydrologic context at these selected locations in relation to annual exceedance probability (AEP) estimates for the April– timing, rank, flood frequency, temporal trends, and histori- May 2017 peak streamflows indicate that peaks at 5 USGS cal flooding. The flood peak data are reported for 59 USGS streamgages had AEPs of 0.2 percent or less (500-year recur- selected streamgages in the southern Midwest including parts rence interval or greater), and peak streamflows at 15 USGS of Arkansas, Illinois, Indiana, Missouri, and Oklahoma having streamgages had AEPs in the range from greater than 0.2 to more than 25 years of peak streamflow record and, generally 1 percent (500- to 100-year recurrence intervals). having 2017 peak streamflows that were ranked in the top 3 Examination of the magnitude of the temporal changes of the annual peaks of record. Flood frequency characteristics in median annual peak streamflows indicated positive for selected stations are provided through the determination of increases, in general, throughout the study area for each of the the annual exceedance probabilities (AEPs) of the 2017 flood 1930–2017, 1956–2017, 1975–2017, and 1989–2017 analysis peaks for the selected stations. The AEP is the probability, periods. The median increase in peak streamflows was great- or chance, of a flood of a given streamflow magnitude being est in 1975–2017 and 1989–2017 with maximum increases equaled or exceeded in any given year. Documenting the flood of 8 to 10 percent per year. No stations in the 1975–2017 or peaks and AEPs will help put the 2017 floods in historical 1989–2017 analysis period had median negative changes in context aiding public and private entities in flood prepared- peak streamflows. ness, protection, and control. The determination of trends in annual streamflow peaks will provide insight into potential changes in the nature of flooding with time and help further inform agencies involved with flood mitigation efforts. Introduction

Excessive rainfall resulted in flooding on numerous rivers throughout the southern Midwestern United States April–May 2017 Flooding—Antecedent (hereafter referred to as the southern Midwest) in late April Conditions, Chronology, and Magnitude and early May of 2017 (fig. 1). Tropical moisture lifted over a stalled frontal system and caused heavy rains from Texas The 2017 flooding in the southern Midwest was wide- to Ohio between April 28 and May 10 resulting in extensive spread in that it included parts of Arkansas, Illinois, Indiana, flooding from eastern Oklahoma to southern Indiana includ- Missouri, and Oklahoma (fig. 1). The April–May 2017 ing parts of Missouri, Arkansas, and Illinois. The flooding flooding primarily occurred in small basins of less than about resulted in 12 deaths, 7 in Arkansas and 5 in Missouri (Cable 1,000 square miles (mi2) but included stations with drain- News Network, 2017). A total of 84 counties (53 in Missouri age areas as large as 23,400 mi2 (table 1). Streamflow peaks 2 Flooding in the Southern Midwestern United States, April–May 2017

105° 100° 95° 90° 85° 80°

North Dakota

45° South Dakota Wisconsin

Minnesota

Michigan

Iowa Nebraska

Ohio Illinois Missouri M Indiana i 40° s s is si pp i R iver i i R v Kansas Missour er

Wadesville St. Louis

Pleasant View Kentucky Springfield Joplin Eminence Willow Springs Van Buren A Doniphan r k an sa s Tecumseh Riv er Tennessee

Oklahoma Georgetown 35° Cotton Plant DeValls Bluff Caddo Gap

Arkansas

Base from U.S. Geological Survey, 1:2,000,000-scale data, 2005 0 75 150 300 MILES Albers Equal-Area Projection North American Datum of 1983 (NAD83) 0 75 150 300 KILOMETERS EXPLANATION

Flood study area Midwestern United States

Figure 1. The Midwestern United States and flood study area associated with the April–May 2017 flood. April–May 2017 Flooding—Antecedent Conditions, Chronology, and Magnitude 3 on the “big” river (Missouri, Mississippi, Ohio) stations in (fig. 5; National Centers for Environmental Prediction, 2017). the study area during the April–May flooding generally were The result was a convergence of the two fronts producing not ranked in the top 5 at any station. Streamflow peaks of thunderstorms that trained over the same areas yielding abun- record occurred at 21 of the 59 streamgaging stations during dant precipitation for the next 24 to 36 hours (fig. 6). the April–May 2017 flooding included in this report (fig. 2, A series of surface lows that moved northeast along table 1), which is noteworthy given the multi-State spatial the front brought waves of showers and thunderstorms and distribution of the record peaks and that the average record resulted in continuous heavy rainfall across the study area length of the 59 streamgages was 67 years. during the day on Saturday, April 29. Interestingly, this upper level atmospheric pattern was very similar to the upper level pattern that developed during the last historic flooding of Antecedent Streamflow and Weather Conditions December 2015 through January 2016 (Holmes and others, for the 2017 Southern Midwest Flooding 2016), which also affected much of the same study area. As the warm front continued to move north on Sunday, April 30, Much of the area in the southern Midwest that was the cold front swept in behind it from the west bringing an affected by flooding in April–May 2017 began the year with end to the rainfall (National Weather Service, 2017b). The streamflows in the normal (25 to 75 percentile) to below heaviest rainfall amounts during April 28–30 occurred over normal (less than 25 percentile) ranges (USGS, 2017b; extreme northeast Oklahoma and northern Arkansas, across fig. 3A), and only the streamflows in the Illinois section of the southern half of Missouri, southern Illinois, and southern the study area primarily were above normal (greater than Indiana, and included totals of 6 to 10 inches (in.) with some 75 percentile). By February, most of the study area had below isolated higher amounts (figs. 7, 8). Largely as a result of the normal streamflows except some higher than normal stream- April 28–30 rainfall totals, April 2017 was the second wettest flows in southwestern Arkansas (fig. 3B). All stations indicated April on record in Missouri (123 years of record), the third below normal to normal conditions in March with near record wettest in Oklahoma, the eighth wettest in Arkansas, and the lows occurring at several stations in southeast Oklahoma and fifth wettest in Illinois (National Centers for Environmental southwest Arkansas (fig. 3C). These predominantly normal to Information, 2017b). The runoff response from the intense below normal streamflow conditions persisted through mid- precipitation, as indicated by the streamflow hydrographs, April (fig. 3D) before the start of heavy rains in the study area varied in magnitude and temporal distribution (fig. 8). Flood on April 28. peaks during the event occurred between April 29 and May Because streamflow is primarily reflective of precipita- 10, 2017, with the timing of the peaks primarily determined tion conditions, it follows that precipitation for January and by the temporal distribution of precipitation and the size of February 2017 also was average to below normal for much of the drainage area upstream from the streamgage. Stations the study area [National Oceanic and Atmospheric Administra- with peaks occurring on April 29 had drainage areas less than tion (NOAA), National Centers for Environmental Informa- 825 mi2, whereas those stations with the later peaks (White tion, 2017b; fig. 4]. March totals were normal for much of the River at Georgetown, Arkansas, May 8, 2017; White River area with above normal total precipitation in parts of southern at DeValls Bluff, Arkansas, May 10, 2017) were large basins Missouri and northern Arkansas. Early to mid-April precipita- (greater than 22,000 mi2). Peak streamflows at streamgages tion also was slightly below normal for Springfield, Mo., and along the White River also were affected by regulation, which other than a substantial precipitation event during April 4–5, could contribute to the later peaks. The effects of man-made 2017, recorded at Saint Louis, Mo., the remainder of April was regulation and the large drainage area are reflected in the fairly dry over the study area until the last week of the month. hydrograph for the White River at Georgetown, Ark. (station number (no.) 07076750), because the peak was 8 days later Flood Chronology than most streamgages in the study area (fig. 8, table 1). The streamflow peak at the Cache River near Cotton Plant, Ark. A rainfall pattern that led to excessive precipitation (station no. 07077555), similarly was lagged compared to falling over much of the southern Midwest began as a surface other streamgages (fig. 8, table 1). The flood peaks at this low pressure center in the four corners region of the western streamgage were lagged and extended by a combination of the United States on April 27, 2017, that slowly moved south- low gradient (less than 1 foot per mile [ft/mi]) and extensive east over the next 24 hours. On Friday afternoon, April 28, a storage capacity in the wide flood plain containing numer- stationary front that extended from southeast Missouri across ous wetlands. The April 27 to May 10 chronology and spatial west-central Arkansas into south-central Oklahoma began progression in streamflow conditions relative to the long-term moving north as a warm front. As an upper level system distribution of daily streamflows indicates the effects of the moved out of the southern Rockies, tropical moisture from heavy precipitation throughout the study area (film 1). the Gulf of Mexico began to get pulled northward up and over the stationary front. At the upper levels of the atmosphere, the Film 1. Daily distribution of streamflow conditions in the 500 millibar low pressure was centered over Arizona and had study area, April 27–May 10, 2017. Source: U.S. Geological become cutoff from the main flow as it drifted slowly eastward Survey, 2017b. 4 Flooding in the Southern Midwestern United States, April–May 2017

------(ft) 16 15 17 20 16 flood stage Service Weather Weather National 1/52 2/52 3/95 3/49 3/48 1/66 6/31 2/58 4/53 4/44 6/43 3/49 7/54 Rank/ 15/60 10/74 3 in record number of annual peak streamflows

7.46 (ft) 21.23 17.14 36.55 23.08 43.06 13.84 19.71 19.21 33.57 21.85 22.36 24.81 28.39 24.68 Peak stage peak Date of Flood of April–May 2017 1 streamflow 2017-04-29 2017-04-30 2017-05-02 2017-05-01 2017-04-30 2017-04-29 2017-04-30 2017-04-29 2017-05-01 2017-04-30 2017-04-30 2017-04-30 2017-04-30 2017-04-30 2017-04-30 - /s) 3 9,090 4,010 9,300 4,010 Peak flow (ft 11,200 11,400 19,000 12,200 16,000 10,300 32,900 18,400 21,000 33,300 27,600 2 stream peak 2013 2008 1935 2015 1996 2008 1973 2009 2015 1993 2015 1909 1994 2015 2015 stage Year of Year

/s, cubic foot per second; ft, foot; --, data not available] 3 21.06 18.41 42.29 27.17 44.4 13.74 22.23 21.88 33.52 27.56 23.86 27.7 30.95 27.81 10.55 (ft) 4 5 Peak stage - 2013 2008 2008 2015 1996 2008 1973 2009 1985 1993 2015 1958 1994 2015 1990 flow peak , square mile; ft 2 Year of Year stream - /s) 3 Historical peak streamflow and stage flow 1 Peak (ft 17,700 29,500 20,400 16,100 23,400 10,000 13,700 14,200 33,000 36,100 13,700 37,000 61,500 38,200 12,600 stream peak recorded streamflow Date of first 5/18/1966 4/28/1966 2/3/1923 9/17/1969 5/1/1970 4/13/1952 3/6/1948 5/30/1967 6/7/1949 4/4/1965 3/10/1974 6/10/1923 11/4/1974 1/30/1969 5/6/1929

) 2 31.7 75.1 69.8 104 147 244 212 129 561 257 420 276 100 (mi area 1,292 1,810 Drainage

USGS streamgage name Wadesville, Indiana Wadesville, near Carrier Mills, Illinois Illinois Edwardsville, Illinois Illinois Heckler, near Marion, Illinois Fayette, Missouri Columbia, Missouri City, Jefferson Missouri Dadeville, Missouri J below Stockton, Missouri View, Pleasant Missouri Caplinger Mills, Missouri near Polk, Missouri Bennett Springs, Missouri Big Creek near South Fork Saline River Cache River at Forman, Cahokia Creek at Richland Creek near Crab Orchard Creek Moniteau Creek near Hinkson Creek at Moreau River near Sac River near Sac River at Highway Cedar Creek near Sac River near River Terre Pomme de Bennett Spring at USGS number 03378550 03382100 03612000 05587900 05595200 05597500 06909500 06910230 06910750 06918440 06919020 06919500 06919900 06921070 06923500 streamgage Peak streamflow and stage data at selected U.S. Geological Survey streamgages in the flood study area for of April–M ay 2017.

1 2 3 4 5 6 7 8 9 11 10 12 13 14 15 (fig. 2) Map ID Table 1. Table in bold denote peak of record streamflows; ID, identifier; USGS, U.S. Geological Survey; mi [Values April–May 2017 Flooding—Antecedent Conditions, Chronology, and Magnitude 5

------8.5 (ft) 11 21 15 20 12 15 16 19 16 21 16 10 flood stage Service Weather Weather National 6/63 1/73 1/88 1/99 1/78 3/26 1/87 1/68 3/96 3/88 2/29 2/26 3/96 Rank/ 1/102 5/104 2/100 3 in record number of annual peak streamflows

(ft) 21.00 39.74 30.67 35.06 37.46 16.90 28.71 36.38 29.38 33.54 30.09 46.11 29.00 27.32 33.42 37.13 Peak stage peak Date of Flood of April–May 2017 1 streamflow 2017-04-30 2017-04-30 2017-04-30 2017-05-01 2017-05-02 2017-04-30 2017-04-30 2017-04-30 2017-05-02 2017-04-30 2017-05-01 2017-05-02 2017-04-30 2017-04-30 2017-04-30 2017-04-30 - /s) 3 Peak flow (ft 90,200 26,200 62,200 95,300 43,800 66,900 62,600 69,700 69,300 27,400 2 stream 110,000 119,000 197,000 190,000 169,000 126,000 peak 1998 2008 1982 2015 2015 1966 1998 1915 2015 1993 1915 2015 2008 1993 1993 1982 stage Year of Year

/s, cubic foot per second; ft, foot; --, data not available] 3 33.5 24.84 34.92 24.5 31.92 34.56 17.74 27.22 34.31 30.33 30.2 46.06 30.47 33.1 36.1 35.77 (ft) Peak stage - 1916 1982 2015 2015 1966 1915 1915 1982 1993 1915 1915 2008 1993 1993 1982 1998 flow peak , square mile; ft 2 Year of Year stream - /s) 3 Historical peak streamflow and stage flow 1 Peak (ft 90,000 81,200 34,900 60,000 90,000 73,300 59,800 80,000 41,800 stream 114,000 140,000 143,000 175,000 130,000 161,000 155,000 peak recorded 1897 1915 6 6 streamflow 8/1915 8/1915 Date of first 4/28/1922 1/6/1897 1/6/1897 2/10/1966 8/20/1915 6 1/4/1950 8/21/1915 3/28/1904 5/17/1920 2/28/1987 11/23/1983 6/8/1937 6

) 2 257 560 199 781 808 735 917 423 505 664 956 (mi area 1,250 2,840 3,180 1,475 3,788 Drainage

USGS streamgage name Big Piney, Missouri Big Piney, Jerome, Missouri Rich Fountain, Missouri Station, Missouri Steelville, Missouri Sullivan, Missouri Union, Missouri Richwoods, Missouri Byrnesville, Missouri Eureka, Missouri Missouri Mill Creek, Missouri Saco, Missouri Patterson, Missouri Westphalia, Missouri Westphalia, Hazelgreen, Missouri Big Piney River near Gasconade River at Gasconade River near Meramec River at Cook Meramec River near Meramec River near Bourbeuse River at Big River near Big River at Meramec River at Castor River at Zalma, St. Francis River near St. Fancis River near St. Francis River near Maries River at Gasconade River near USGS number 06930000 06933500 06934000 07010350 07013000 07014500 07016500 07018100 07018500 07019000 07021000 07035800 07036100 07037500 06927000 06928000 streamgage Peak streamflow and stage data at selected U.S. Geological Survey streamgages in the flood study area for of April–M ay 2017.—Continued

18 19 20 21 22 23 24 25 26 27 28 29 30 31 16 17 (fig. 2) Map ID Table 1. Table in bold denote peak of record streamflows; ID, identifier; USGS, U.S. Geological Survey; mi [Values 6 Flooding in the Southern Midwestern United States, April–May 2017

------7 8 (ft) 12 15 20 16 16 12 20 13 17 15 flood stage Service Weather Weather National 4/63 6/29 2/96 1/33 1/73 1/63 3/79 1/96 1/77 1/97 1/86 2/27 Rank/ 10/69 12/96 1/106 1/101 3 in record number of annual peak streamflows

9.15 (ft) 18.99 20.90 35.97 31.87 41.82 33.07 23.3 21.96 27.72 37.42 33.13 28.95 28.66 27.9 33.99 Peak stage peak Date of Flood of April–May 2017 1 streamflow 2017-05-01 2017-04-30 2017-04-29 2017-04-30 2017-04-30 2017-04-29 2017-04-29 2017-04-30 2017-05-01 2017-04-30 2017-04-30 2017-05-01 2017-05-02 2017-04-30 2017-05-01 2017-05-04 - /s) 3 9,500 4,220 Peak flow (ft 38,100 82,800 95,200 71,200 29,700 2 111,000 stream 189,000 106,000 179,000 183,000 105,000 124,000 137,000 173,000 peak 2011 2011 2011 1945 2015 2015 2008 1985 1982 1993 2008 1904 1904 1982 1982 1982 stage Year of Year

/s, cubic foot per second; ft, foot; --, data not available] 3 22.2 22.15 25.49 19.85 10.16 35.96 31.51 28.1 26.74 27.38 29.0 28.44 21.64 29.06 34.77 (ft) Peak stage 4 25.0 - 2011 2011 1989 1909 2015 2008 1990 1985 1982 1993 1904 1993 1904 1904 1982 1982 flow peak , square mile; ft 2 Year of Year stream - /s) 3 6,710 Historical peak streamflow and stage flow 1 Peak (ft 12,200 62,000 85,100 38,500 75,000 71,100 58,500 86,600 49,800 stream 109,000 100,000 153,100 130,000 162,000 212,000 peak recorded streamflow 7/1909 3/1904 3/1904 6/1945 Date of first 6 11/1/1972 4/1/1922 2/23/1985 4/15/1945 4/14/1945 4/17/1939 6 11/19/1921 3/26/1904 6 4/17/1927 8/20/1915 1/14/1930 12/4/1982 6

) 2 31.4 450 246 987 398 561 570 484 398 793 (mi area 1,245 1,667 2,038 4,840 1,130 8,420 Drainage

USGS streamgage name Springfield, Missouri Springfield, Missouri Missouri Yellville, Crossing at Arkansas Missouri Tecumseh, Missouri Tecumseh, Annapolis, Missouri Missouri Bluff, Missouri Buren, Missouri Doniphan, Missouri Arkansas Pocahontas, Missouri Bardley, Ravenden Springs, Arkansas Arkansas Ferry, near Morehouse, Missouri James River near Creek near Wilson James River at Galena, Crooked Creek at Kelly North Fork River near Bryant Creek near Black River near Black River at Poplar Jacks Fork at Eminence, Van Current River at Current River at Black River at Eleven Point River near Eleven Point River near Black River at Elgin Little River Ditch No. 1 USGS number 07050700 07052100 07052500 07055607 07057500 07058000 07061500 07063000 07066000 07067000 07068000 07069000 07071500 07072000 07074420 07043500 streamgage Peak streamflow and stage data at selected U.S. Geological Survey streamgages in the flood study area for of April–M ay 2017.—Continued

33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 32 (fig. 2) Map ID Table 1. Table in bold denote peak of record streamflows; ID, identifier; USGS, U.S. Geological Survey; mi [Values April–May 2017 Flooding—Antecedent Conditions, Chronology, and Magnitude 7

------(ft) 11 21 10 19 14 15 13 flood stage Service Weather Weather National 1/38 3/67 1/31 2/30 8/95 4/94 2/78 2/58 1/62 3/58 3/61 3/29 Rank/ 3 in record number of annual peak streamflows

(ft) 31.5 31.31 20.25 18.44 28.14 22.96 27.39 16.94 30.12 18.31 23.57 23.32 Peak stage peak Date of Flood of April–May 2017 1 streamflow 2017-05-08 2017-05-10 2017-05-05 2017-04-29 2017-04-30 2017-04-29 2017-04-29 2017-04-29 2017-04-30 2017-04-29 2017-04-30 2017-04-30 - /s) 3 Peak flow (ft 10,100 30,400 55,800 52,900 19,900 19,400 18,000 35,800 2 stream 200,000 187,000 107,000 128,000 peak 2011 2011 2011 2015 1993 1941 1941 1975 2015 1974 1982 1993 stage Year of Year

/s, cubic foot per second; ft, foot; --, data not available] 3 33.95 36.1 20.28 20.33 34.06 28.4 22.07 28.64 19.42 29.29 26.27 (ft) Peak stage 4 28.0 A rank of 1 indicates that the April–May 2017 peak streamflow was higher than all other rank of 1 indicates that the A - 1982 1949 1987 2015 1993 1943 1941 1975 2015 1974 1982 1993 flow peak , square mile; ft 2 Year of Year stream - /s) 3 9,950 Historical peak streamflow and stage flow 1 Peak (ft 40,600 62,100 39,800 44,400 24,200 97,200 stream 110,000 179,000 220,000 151,000 137,000 peak recorded 1923 6 streamflow Date of first 4/6/1979 6/28/1928 7/13/1987 7/6/1967 7/13/1924 4/12/1940 5/6/1960 5/15/1956 5/15/1956 3/21/1955 11/19/1988

) 2 110 425 427 851 133 635 169 136 (mi area 1,170 1,164 22,400 23,400 Drainage

USGS streamgage name Georgetown, Georgetown, Arkansas Arkansas Bluff, Arkansas Plant, Carthage, Missouri Missouri Joplin, Missouri Missouri Sycamore, Oklahoma Oklahoma Watts, Oklahoma Arkansas Arkansas Gap, White River at White River at Devalls Cache River near Cotton Spring River at Waco, Spring River near Shoal Creek above City, Tiff Elk River near Spavinaw Creek near Illinois River near Flint Creek near Kansas, Cadron Creek near Guy, Caddo River near USGS number 07076750 07077000 07077555 07185765 07186000 07187000 07189000 07191220 07195500 07196000 07261000 07359610 streamgage Peak streamflow and stage data at selected U.S. Geological Survey streamgages in the flood study area for of April–M ay 2017.—Continued

48 49 50 51 52 53 54 55 56 57 58 59 All peak streamflow and stage information obtained from U.S. Geological Survey (2017a). At the time of this report, peak streamflows in water year 2017 (from October 1, 2016, to September 30, 2017) are provisional data subject revision. Rank of the maximum instantaneous peak streamflow compared to all systematic and historical annual peaks. location or datum from current streamgage. Stage obtained at different Maximum stage known, 27.7 feet, July 29, 1909, from floodmark. Month or day of occurrence is unknown not exact. 1 2 3 4 5 6 (fig. 2) Map ID Table 1. Table in bold denote peak of record streamflows; ID, identifier; USGS, U.S. Geological Survey; mi [Values recorded annual peak values. 8 Flooding in the Southern Midwestern United States, April–May 2017

94° 92° 90° 88° 40° Illinois

Missouri #7 #8 #4 Indiana Miss ouri R iver 27 9 24 # # 16 # 26 5 # #20 # # Kansas #1 #23 #25 22 19 # 38° 13 # 21 6 12# 17 # # 2 # 11 15 # 18 # 14 r # # # e # 29 v Cu # 3 i rr 30 R 10 e # o nt R 39 # i # iv # h er 31 28 O 52 Ja 41 # 51 34 c rk # # 33 ks Fo # Kentucky # # # 42 #53 2 3 # 32 E 40 # 35 EE # # 5 E 45 43 54 E 4 # # # 38 #E# 6 377 #46 55 #44 # #36 57##56 r e Tennessee v 36° i 47 R

# i p ip s is s is 58 M # r e 48 v

R # 50

t #

i h

W #49

#59 Oklahoma Mississippi Alabama 34° Arkansas Texas

Base from U.S. Geological Survey, 1:2,000,000-scale data, 2005 Albers Equal-Area Projection 0 25 50 100 MILES North American Datum of 1983 (NAD8 EXPLANATION 0 25 50 100 KILOMETERS 27 # U. S. Geological Survey streamgage and identifier 2 E Film location and identifier (table 2)

Flood study area

Figure 2. Location of selected U.S. Geological Survey streamgages and aerial video documentation locations within the designated flood study area. April–May 2017 Flooding—Antecedent Conditions, Chronology, and Magnitude 9

96° 94° 92° 90° 88° 86°

Missouri Illinois A. Indiana

Kansas 38°

Kentucky

Tennessee January 15, 2017 36° Stream ow condition New low Less than 5 to 9 percentile 10 to 24 percentile Oklahoma 25 to 75 percentile 76 to 90 percentile Greater than 90 percentile 34° Texas Arkansas Flood study area

96° 94° 92° 90° 88° 86°

Missouri Illinois B. Indiana

Kansas 38°

Kentucky

Tennessee

36° February 15, 2017

Oklahoma Alabama Mississippi 34° Texas Arkansas

Base from U.S. Geological Survey, 1:2,000,000-scale data, 2005 0 50 100 MILES Albers Equal-Area Projection North American Datum of 1983 (NAD83) 0 50 100 KILOMETERS Figure 3. Streamflow conditions at selected U.S. Geological Survey streamgages in the study area before the April–May 2017 flooding including A, January ; B, February; C, March; and D, April of 2017. 10 Flooding in the Southern Midwestern United States, April–May 2017

96° 94° 92° 90° 88° 86°

Missouri Illinois C. Indiana

Kansas 38°

Kentucky

Tennessee

36° March 15, 2017 Stream ow condition New low Less than 5 to 9 percentile 10 to 24 percentile Oklahoma 25 to 75 percentile 76 to 90 percentile

34° Greater than 90 percentile Texas Arkansas Flood study area

96° 94° 92° 90° 88° 86°

Missouri Illinois D. Indiana

Kansas 38°

Kentucky

Tennessee

36° April 15, 2017

Oklahoma Alabama Mississippi 34° Texas Arkansas

Base from U.S. Geological Survey, 1:2,000,000-scale data, 2005 0 50 100 MILES Albers Equal-Area Projection North American Datum of 1983 (NAD83) 0 50 100 KILOMETERS

Figure 3. Streamflow conditions at selected U.S. Geological Survey streamgages in the study area before the April–May 2017 flooding including A, January; B, February; C, March; and D, April of 2017.—Continued April–May 2017 Flooding—Antecedent Conditions, Chronology, and Magnitude 11

January 2017 February 2017

March 2017 April 2017 EXPLANATION Monthly precipitation condition

Study area boundary

Figure 4. Monthly precipitation conditions in the United States for January–April 2017, as a percent of normal. (Modified from NOAA, National Centers for Environmental Information, 2017b).

USGS hydrologic technician tethering acoustic Doppler current profiler (ADCP), St. Francis River near Patterson, Mo., April 30, 2017. Photograph by Aaron Walsh, USGS. 12 Flooding in the Southern Midwestern United States, April–May 2017

Figure 5. 500 millibar height contours for April 29, 2017, across the continental United States (Source: National Centers for Environmental Prediction, 2017).

Illinois River near Watts, Okla., April 30, 2017. Photograph by U.S. Geological Survey. April–May 2017 Flooding—Antecedent Conditions, Chronology, and Magnitude 13

April 29, 2017

EXPLANATION Precipitation area H High-pressure area 1020 Isobar and value L Low-pressure area Frontal line between high- and low-pressure systems April 30, 2017

Figure 6. Daily surface weather maps at 7:00 AM Eastern Standard Time from April 29 to 30, 2017 (Source: National Centers for Environmental Prediction, 2017). 14 Flooding in the Southern Midwestern United States, April–May 2017

Wisconsin Michigan

Iowa Nebraska Illinois Missouri Indiana

Kansas Kentucky

Oklahoma Tennessee

Alabama Arkansas Mississippi Texas Georgia

Figure 7. Cumulative rainfall totals over the southern Midwest United States during April 28–30, 2017. Source:Figure National 7. Cumulative Weather Service rainfall (2017b). totals over the southern Midwest United States during April 28 - 30, 2017. Source: National Weather Service (2017b).

Southern Current River near Doniphan, Mo., May 1, 2017. Photograph by Ben Rivers, USGS. April–May 2017 Flooding—Antecedent Conditions, Chronology, and Magnitude 15

60,000 0 0 0 0 0 0 0 0 0 0.35 0.3 0.5 50,000 0.5 1 20,000 0 0 0 0 0 0 0 0.95 0.02 18,000 0.06 40,000 Shoal Creek above Joplin, MO 1.5 1 Station 07187000 2 16,000 0.95 1.36 30,000 14,000 2 Precipitation from Joplin 5.2 SSW 2.5 1.78 1.81 12,000 20,000 3 Big Creek near Wadesville, IN 3 10,000 Station 03378550 3.5 8,000 4 10,000 in inches Precipitation, Precipitation from Poseyville 2.8 NW 4 3.87 6,000 station 5 0 4.5

Stream ow, in cubic feet per second in cubic feet Stream ow, 4,000 4/28 4/29 4/30 5/1 5/2 5/3 5/4 5/5 5/6 5/7 5/8 5/9 6 in inches Precipitation, 2,000 Date 6.05 0 7 Stream ow, in cubic feet per second in cubic feet Stream ow, 4/28 4/29 4/30 5/1 5/2 5/3 5/4 5/5 5/6 5/7 5/8 5/9 5/10 Date Missouri Illinois

Jefferson City 5.9 W Union 0.8 NE Indiana (5.81,9.18) (5.23,9.53) Red Bud 5 SE (5.03,8.36) Poseyville 2.8 NW # Kansas (7.41, 12.03) Steelville 5.6 SW Herrin 3.4 S (7.70,11.79) (8.56,11.49) Springfield 0.7 ENE Winona Forest Ranger Station (5.61,7.91) 200,000 0 Joplin 5.2 SSW (9.29,11.92) 0 0 0 0 0 0 0 (5.68,8.33) # 180,000 0.09 # Poplar Bluff 4.2 NW 0.66 1 (7.40,8.92) 160,000 0.97 2 Upper Spavinaw Port West Plains 1.5 NW 140,000 1.8 1.83 (9.29,13.55) (5.17, 5.97) 120,000 Current River at Van Buren, MO 3 Pocahontas 1 100,000 Station 07068000 Clinton 6 SE 4 Westville 0.2 ENE (4.05, 6.77) 80,000 Preciptitation from Winona Forest (2.95,4.59) (5.56,5.61) 60,000 Ranger Station Georgetown 5 40,000 (7.82,10.10) 6 in inches Precipitation, # 20,000 6.57 Mount Ida 4 S # 0 7 Oklahoma per second in cubic feet Stream ow, 4/28 4/30 5/2 5/4 5/6 5/8 5/10 (5.9, 8.35) Date 12,000 0 0 0 0 0 0 0 0 0 0 0 0.33 0.26 0.38 1 10,000 2 1.69 8,000 3

Arkansas Cache River near Cotton Plant, AR 4 6,000 Station 07077555 5 250,000 0 0 0 0 0 0 0 0 0 0 0 4,000 6 0.33 0.26 0.38 1 Precipitation from Georgetown station 7 200,000 2 2,000 1.69 8 in inches Precipitation, 3 7.82 0 9

150,000 per second in cubic feet Stream ow, 4 4/28 4/30 5/2 5/4 5/6 5/8 5/10 5/12 White River at Georgetown, AR 5 Date 100,000 Station 07076750 6 EXPLANATION Precipitation from Georgetown 50,000 7 0.26 Daily precipitation and value (National Centers for station in inches Precipitation, 8 Environmental Information, 2017a) 7.82 0 9 Stream ow hydrograph Stream ow, in cubic feet per second in cubic feet Stream ow, 4/28 4/30 5/2 5/4 5/6 5/8 5/10 5/12 Precipitation station Date Red Bud 5 SE (April 28-30 total precipitation, Figure 8. Streamflow hydrographs and precipitation totals and (5.03,8.36) April 28-May 10 total precipitation, in inches) distributions for selected U.S. Geological Survey streamgages and precipitation stations within the study area. Flood study area 16 Flooding in the Southern Midwestern United States, April–May 2017

Magnitude of April–May 2017 Flooding and that also were near USGS streamgage locations with peaks of record during the flood including North Fork River Peak-of-record streamflows were set at 21 USGS near Tecumseh, Mo. (fig. 2 map ID 37; table 1) and Bryant streamgages in the southern Midwest during the resulting Creek near Tecumseh, Mo. (fig. 2 map ID 38; table 1). April–May 2017 flooding (table 1). Each of the five States included in the study area had at least one streamgage with Film 2. Spring Creek at Highway AP bridge near Willow Springs, a peak of record during the flood. In Missouri, the previous Missouri, April 30, 2017, at 10:30 a.m. (see fig. 2 aerial video peaks of record (for stage) at two rivers (Jacks Fork, Current location 1). (Video footage provided by Aerial Ozarks). River) had stood since 1904 and included 96 to 106 annual peaks. The peak stage of the April–May 2017 flood at the Film 3. North Fork River and Spring Creek at Highway 14, Current River at Van Buren, Mo. (station no. 07067000), Douglas County, Missouri, April 30, 2017, at 12:09 p.m. (see fig. 2 exceeded the previous maximum stage by 8.4 ft (table 1). aerial video location 2). (Video footage provided by Aerial Ozarks). Most remaining streamgages included in the study had peak streamflows during the event that ranked in the top three peaks Film 4. North Fork River at Highway CC, Ozark County, Missouri, of record. Additional USGS streamgages within the study area, April 30, 2017, at 12:37 p.m. (see fig. 2 aerial video location 3). but on the perimeter of the storm track, had peaks that ranked (Video footage provided by Aerial Ozarks). as low as the top 10–15 (table 1) including the Moniteau River near Fayette, Mo. (map identifier [ID] 7), and Cedar Creek Film 5. Bryant Creek at Highway 181, Ozark County, Missouri, near Pleasant View, Mo. (map ID 12), along the northern April 30, 2017, at 13:06. (see fig. 2 aerial video location 4). (Video boundary of the study area (fig. 2). footage provided by Aerial Ozarks). Flooding is easily summarized numerically as a peak stage or streamflow value, but these numbers alone fail to Film 6. North Fork River at Highway PP near Tecumseh, convey the physical consequences of such high flows on struc- Missouri, Ozark County, April 30, 2017, at 13:40. (see fig. 2 aerial tures and the lives of those affected. Aerial videos that were video location 5). (Video footage provided by Aerial Ozarks). collected within 24 hours of the flood peaks at several locations (table 2, fig. 2) document the consequences of the floods Film 7. Dry Creek at Highway AP near Willow Springs, Missouri, (films 2–7). These videos were collected at locations within April 30, 2017, at 15:29. (see fig. 2 aerial video location 6). (Video the greater than 10 in. precipitation areas shown in figure 7, footage provided by Aerial Ozarks).

Table 2. Date, times, and locations of aerial video footage documenting the effects of the April–May 2017 flood at selected locations in south-central Missouri.

[ID, identifier; Lat, lattitude; Long, longitude; hwy, highway; nr, near; MO, Missouri]

Map ID (fig. 2) Film Lat Long Date Time Description 2 2 36.9074051 -92.0808668 4/30/2017 10:30 Spring Creek at Hwy AP bridge, nr Willow Springs, MO. 3 3 36.810436 -92.1498827 4/30/2017 112:09 North Fork River and Spring Creek at Hwy 14, Douglas County, MO. 4 4 36.7598273 -92.1556513 4/30/2017 112:37 North Fork River at Hwy CC, Ozark County, MO. 5 5 36.7095049 -92.2690143 4/30/2017 213:06 Bryant Creek at Highway 181, Ozark County, MO. 6 6 36.615802 -92.262483 4/30/2017 113:40 North Fork River at Hwy PP nr Tecumseh, Ozark County, MO. 7 7 36.8378767 -92.0559632 4/30/2017 15:29 Dry Creek at Highway AP, near Willow Springs, Howell County, MO. 1The peak at the nearby North Fork River near Tecumseh, Missouri, streamgage was at 4/29/17 at 21:45. 2The peak at the nearby Bryant Creek near Tecumseh, Missouri, streamgage was at 4/29/17 at 20:00. April–May 2017 Flooding—Annual Exceedance Probability 17

April–May 2017 Flooding—Comparison it has occurred, will not occur again for another 99 years, which is not necessarily true. A 100-year flood means that, if with Historic Floods all things remain the same in the basin (for example, land use and climate conditions), the observed annual floods during Placing the magnitude of a flood into context is desirable thousands of years would average around 100 years between for comparison with previous floods. Ranking the observed events of this magnitude. The term annual exceedance prob- 2017 peak streamflows at USGS streamgages against previ- ability (AEP) is now more commonly used to refer to flood- ous streamflow peaks of record indicates the relative magni- frequency estimates because it more clearly conveys that the tude of the 2017 floods (table 1, fig. 9). The benchmark for flood-frequency estimates are probabilistic in nature. The AEP major flooding on many of the major tributaries in the study is the probability that the streamflow of a certain magnitude area includes the 1982 (Sauer and Fulford, 1983), 1993 will be equaled or exceeded in any year and is the recipro- (Parret and others, 1993), and December–January 2015–16 cal of the recurrence interval. A 0.01 AEP streamflow, for floods (Holmes and others, 2016). Each of the 1982, 1993, example, has a 1-percent chance of occurring in any year and and 2015–16 floods resulted in 8 peaks of record among is equivalent to a 100-year flood streamflow. the selected stations included in this study, whereas the The current (2017) standard methodology for the deter- 2017 flood resulted in 21 peaks of record. The number of mination of flood-frequency studies is Bulletin 17C (England streamgages in operation did vary considerably with time, but and others, 2017) of the Advisory Committee on Water nearly the same number of streamgages were in operation in Information. Similar to the Bulletin 17B method (Interagency 1982 (54 streamgages) as were in operation during the 1993, Advisory Committee on Water Data, 1982), the Bulletin 17C 2015–16, and 2017 floods (59 streamgages; fig. 9). method fits a log-Pearson Type III distribution curve to the logarithms of annual peak discharges at a given station using the method-of-moments to compute a mean, standard devia- April–May 2017 Flooding—Annual tion, and station skew of the log-transformed peak flow data. The user has the option to weigh the individual station skew Exceedance Probability estimate with a generalized/regional skew estimate, which typically improves the accuracy because skews tend to follow In the past, flood-frequency estimates have been regional trends. Modifications incorporated into the Bulle- presented in terms of the recurrence interval, which repre- tin 17C method include the adoption of a generalized method- sents the average number of years between occurrences of a of-moments estimator, known as the expected moments streamflow of equal or greater magnitude. This term, however, algorithm (EMA) procedure (Cohn and others, 1997), and a often results in a misunderstanding that a 100-year flood, once generalized version of the Grubbs-Beck test for low outliers

25 60 Annual number of peaks of record 50 a k 20 p e Number of stations h d t r with peak streamﬂow i 40 o w c

15 record s r e n

o w

30 o a ti ﬂ s t

10 f a m o

e r

20 r e s t b

5 m 10 u N Annual number of peaks record 0 0 1900 1920 1940 1960 1980 2000 2020 Date

Figure 9. Annual number of peak-of-record streamflows and number of U.S. Geological Survey streamgages in the study area with peak streamflow record. 18 Flooding in the Southern Midwestern United States, April–May 2017

(Cohn and others, 2013). The EMA is an updated method for Temporal Changes in Annual Peak fitting the log-Pearson Type III frequency distribution that is a more effective means of incorporating historical peak stream- Streamflows flow information into a flood-frequency analysis. The USGS computer program PEAKFQ (version 7.1; Temporal changes in annual peak streamflows are impor- Flynn and others, 2006) was used to compute the flood- tant to investigate because they may indicate to emergency and frequency estimates for the 59 stations in this study. The infrastructure managers there are corresponding changes in the annual peak streamflow data used in the analyses were levels of risk to public safety. Temporal changes in streamflow obtained from U.S. Geological Survey (2017a). The program can be the result of changes to such factors as land use and automates many of the flood-frequency analyses procedures, land cover, climate, or regulation. The annual peak streamflow including identifying and adjusting for high and low outli- time series data were analyzed for selected streamgages in the ers and historical periods and fitting the log-Pearson Type III southern Midwest to determine the presence and subsequent distribution to the streamflow data. The program includes the magnitude of changes through time at each site. EMA procedure for flood-frequency analysis and multiple The temporal changes in streamflow magnitudes were Grubbs-Beck outlier screening (Veilleux and others, 2013). computed based on the Sen’s slope estimator (Sen, 1968) The PEAKFQ program and associated documentation are using the MAKESENS application from the Finnish Meteo- available at https://water.usgs.gov/software/peakfq.html. rological Institute (Salmi and others, 2002). The Sen’s slope, In addition to estimating the at-site AEP flood quantiles also known as the Kendall-Theil robust line, is a nonparamet- by Bulletin 17C methods, another way to obtain an AEP flood ric estimate of trend magnitude slope for a univariate time quantile estimate is by using regional regression equations series when the time interval is constant (equally spaced). (RREs). The RREs are developed using regression techniques that relate the peak flood-probability data at many streamgages f(t) = Mq×t + B (1) in a particular region to the basin characteristics upstream from the streamgages (Jennings and others, 1994). The RREs where allow a user to estimate the various AEP flood quantiles for f(t) is the increasing or decreasing function any location along a stream (gaged or ungaged) by entering of time for the trend magnitudes of the the specified basin characteristics (for example, drainage area streamflows used in the investigation, or average precipitation) used as independent variables in the Mq is the Sen’s slope estimate, equation. Rural regression estimates for the 59 streamgages t is time, and in this study were obtained from the corresponding RRE B is a constant. estimates developed for each state in the study area including Arkansas (Wagner and others, 2016), Illinois (Soong The Sen’s slope is the median slope of all pairwise and others, 2004), Missouri (Southard, 2010; Southard and comparisons with each pairwise difference divided by the Veilleux, 2014), and Oklahoma (Lewis, 2010). The single number of years separating the records. To determine the Sen’s streamgage in Indiana (Big Creek near Wadesville, Indiana) is slope estimate in equation 2, the slopes of all data pairs are within 10 mi of the Illinois border, so the Illinois RRE equa- calculated: tions were used to obtain the RRE estimates for this station. The optimal estimate of the AEP flood quantile for a gaged site ()XX− M , = kj is determined by weighting the at-site AEP flood quantile esti- jk for j=1,..., n−1; j < k ≤ n (2) ∆t jk, mate determined from the Bulletin 17C methods with the AEP flood quantile estimate determined from the RRE as described where M is the slope between data points X and X ; in (Soong and others, 2004; Southard, 2010; Southard and j,k j k X is the data measurement at time j; Veilleux, 2014; and Wagner and others, 2016). j X is the data measurement at time k; The AEP estimates for the April–May 2017 flood peak k Δt is the change in time between observations; streamflows indicate that peaks at 5 USGS streamgages had an j,k AEP of 0.2 percent or less, and peak streamflows at 15 USGS and streamgages had an AEP in the range from greater than 0.2 n is the number of years of record. to 1 percent (table 3, fig. 10). The weighted estimates of the The Sen’s slope estimate, M , is equal to the median value of AEP flood quantiles corresponding to the 50-, 20-, 10-, 4-, q all the M values. 2-, 1-, 0.5-, and 0.2-percent AEPs, along with their respective j,k 95-percent confidence limits, for the selected 59 streams in the southern Midwest included in this study, also were computed (table 3). Temporal Changes in Annual Peak Streamflows 19

Streamgages with missing record periods exceeding annual peak streamflows of increasing magnitude (fig. 11C). 5 percent of the total record were not used in the analyses Six of the 44 stations in the 1975–2017 analysis period had of temporal changes in annual streamflow peaks nor were positive changes of greater than 2 percent, whereas 23 of streamgages on regulated rivers. Of the 59 streamgages 49 stations in the 1989–2017 analysis period had median included in the study, 49 were used in the analyses of tempo- positive increases of greater than 2 percent with maximum ral changes in annual peak streamflows. The start dates of increases of 8–10 percent per year (fig. 11D). No stations in documented peak streamflows and record periods for the either of the 1975–2017 or 1989–2017 analysis periods had 49 stations differed; therefore, four temporal analysis periods median negative changes in peak streamflows, but five stations (1930–2017, 1956–2017, 1975–2017, and 1989–2017) were in the 1989–2017 analysis period had no change in streamflow selected to maintain consistency in streamflow record start peaks. dates, have overlap of record analysis periods, and maximize A primary driver of change in peak streamflows is the number of stations and the period of record that could precipitation. Similar to streamflow peaks, the annual precipi- be included in the analyses. For comparison of streamgages tation within the flood study area was analyzed by climate with differing basin sizes, the Sen’s slope for each streamgage division (NOAA, National Centers for Environmental Infor- was divided by the median annual peak streamflow value to mation, 2017c) using the Sen’s slope methodology. Changes determine the percentage of change with respect to the median in annual precipitation were analyzed for the same periods as annual peak streamflow at each streamgage. peak streamflow except the analysis periods for precipitation Examination of the magnitude of the temporal changes ended in 2016. Similar to changes in annual peak streamflows, (scaled by median annual peak flood streamflow) in median median changes in annual precipitation for the 1930–2016 annual peak streamflows from 1930–2017 indicates all but 1 and 1956–2016 periods generally were small (less than of the 20 stations included had a systematic positive increase 2 percent) and positive (fig. 12). Changes in annual precipita- in peak streamflows of less than 2 percent per year (fig. 11A). tion, however, provided little explanation for the substantial The remaining station, Shoal Creek above Joplin, Mo. increase in magnitude of streamflow peaks because, for (station no. 07187000, map ID 53), had a negative change example, nearly one-half of the climate divisions in the 1989– of -0.12 percent per year during the analysis period. Simi- 2016 analysis period indicated no change or a negative change larly, the temporal change in peak streamflows at most of the in precipitation per year, whereas this was the period of the 34 stations included in the 1956–2017 analysis period had greatest magnitude in positive changes in streamflow peaks in median positive increases in annual peak flows of less than the study area. The increase in the frequency of larger magni- 2 percent (fig. 11B). Two stations (Jacks Fork at Eminence, tude rain events with time may be a better explanatory variable Mo., station no. 07066000, map ID 41; Current River at for the greater positive changes in annual peak streamflows. Van Buren, Mo., station no. 07067000, map ID 42), had no The frequency of daily precipitation events of greater than 2 change and one station had a median decrease in annual peak or 3 in. generally increased from 1985 to 2014 in each state in streamflows of -0.12 percent per year over the 61-year period the study area (fig. 13). The degree to which land use changes (Cadron Creek near Guy, Ark., station no. 07261000, map may have contributed to the positive changes in peak stream- ID 58). Analyses of the 1975–2017 and 1989–2017 periods flows was undetermined. indicated nearly all stations had median positive changes in 20 Flooding in the Southern Midwestern United States, April–May 2017

Table 3. Estimated annual exceedance probability of the 2017 flood peaks and weighted peak streamflow estimates for selected flood quantiles at 59 U.S. Geological Survey streamgages included in this study.

[ID, identifier; USGS, U.S. Geological Survey; AEP, annual exceedance probability; ft, foot; ft3/s, cubic foot per second; %, percent; --, not calculated; stations with peak of record during April–May 2017 flood are shown with rank value of “1” in bold]

Expected peak streamflows for selected AEP with Expected peak streamflows for selected AEP with 95-percent confidence limits 95-percent confidence limits (ft3/s) (ft3/s) 2017 flood peak AEP for observed 2017 flood 50-percent AEP 20-percent AEP 10-percent AEP 4-percent AEP 2-percent AEP 1-percent AEP 0.5-percent AEP 0.2-percent AEP (2-year recurrence) (5-year recurrence) (10-year recurrence) (25-year recurrence) (50-year recurrence) (100-year recurrence) (200-year recurrence) (500-year recurrence)

67% confidence 95% confidence 95% confidence 95% confidence 95% confidence 95% confidence 95% confidence 95% confidence 95% confidence interval1 limits2 limits2 limits2 limits2 limits2 limits2 limits2 limits2 Map ID (fig. 2) /s) 3 Estimate Rank (ft USGS streamgage name Estimate Estimate Estimate Estimate Estimate Estimate Estimate USGS streamgage number streamflow Recurrence Date of peak AEP estimate Upper Upper Upper Upper Upper Upper Upper Upper Upper Lower Lower Lower Lower Lower Lower Lower Lower Lower Peak stage (ft) interval (years) Peak streamflow peaks in analysis Number of annual

1 03378550 Big Creek near 1 52 4/29/2017 21.23 19,000 0.83% 123 0.4% 3.4% 5,270 4,710 5,890 7,920 6,930 9,050 9,870 8,440 11,500 12,500 10,200 15,200 14,500 11,500 18,300 16,700 12,800 21,800 ------22,000 15,500 31,200 Wadesville, Indiana 2 03382100 South Fork Saline River 2 52 4/30/2017 17.14 12,200 1.4% 72 1.4% 6.1% 3,100 2,720 3,520 5,030 4,310 5,880 6,610 5,480 7,980 8,940 7,050 11,300 10,900 8,260 14,400 13,100 9,500 18,000 ------18,900 12,500 28,600 near Carrier Mills, Illinois 3 03612000 Cache River at Forman, 3 95 5/2/2017 36.55 11,200 3.8% 27 1.5% 4.7% 3,810 3,430 4,230 6,320 5,620 7,100 8,250 7,180 9,470 11,000 9,200 13,100 13,200 10,700 16,200 15,500 12,200 19,700 ------21,400 15,600 29,500 Illinois3 4 05587900 Cahokia Creek at 3 49 5/1/2017 23.08 9,090 7.3% 14 2.9% 9.1% 5,470 5,030 5,950 7,350 6,700 8,050 8,500 7,650 9,450 9,870 8,730 11,200 10,900 9,410 12,500 11,800 10,100 13,900 ------14,000 11,300 17,200 Edwardsville, Illinois 5 05595200 Richland Creek near 3 48 4/30/2017 43.06 16,000 4.9% 20 2.9% 9.2% 5,900 5,070 6,870 9,920 8,460 11,600 12,800 10,700 15,300 16,600 13,400 20,700 19,600 15,300 25,200 22,600 17,000 30,000 ------29,800 20,600 43,100 Heckler, Illinois 6 05597500 Crab Orchard Creek near 1 66 4/29/2017 13.84 10,300 0.91% 110 0.3% 2.7% 1,950 1,670 2,260 3,600 3,030 4,270 4,920 4,020 6,010 6,800 5,310 8,700 8,320 6,250 11,100 9,910 7,140 13,800 ------13,900 9,110 21,300 Marion, Illinois 7 06909500 Moniteau Creek near 15 60 4/30/2017 19.71 4,010 27.9% 4 19.3% 29.9% 2,830 2,500 3,200 4,600 4,010 5,270 5,900 5,070 6,870 7,700 6,420 9,220 9,120 7,430 11,200 10,600 8,420 13,300 12,200 9,400 15,700 14,200 10,600 19,100 Fayette, Missouri 8 06910230 Hinkson Creek at 6 31 4/29/2017 19.21 9,300 10.1% 10 12.1% 25.3% 4,560 3,880 5,360 7,400 6,360 8,610 9,330 7,930 11,000 11,900 9,870 14,300 13,900 11,300 17,100 16,900 12,800 22,200 ------21,700 15,900 29,600 Columbia, Missouri4 9 06910750 Moreau River near 2 58 5/1/2017 33.57 32,900 3.1% 32 1.3% 5.5% 13,600 12,100 15,300 20,600 18,300 23,300 25,300 22,200 28,900 31,200 26,600 36,500 35,400 29,600 42,300 39,600 32,300 48,500 43,700 34,800 54,900 49,200 37,900 64,000 Jefferson City, Missouri 10 06918440 Sac River near Dadeville, 4 53 4/30/2017 21.85 18,400 7.3% 14 4.1% 10.7% 5,270 4,420 6,290 10,500 8,650 12,800 15,300 12,300 18,900 22,900 18,000 29,200 29,200 22,400 38,100 35,900 27,000 48,000 43,000 31,700 58,400 52,100 37,000 73,500 Missouri 11 06919020 Sac River at Highway J 4 44 4/30/2017 22.36 11,400 6.6% 15 4.9% 12.8% 6,860 6,120 7,650 9,120 8,180 10,400 10,500 9,360 12,200 12,100 10,600 14,800 13,300 11,500 16,900 14,400 12,200 19,100 15,400 12,800 21,400 16,700 13,600 24,800 below Stockton, Missouri5 12 06919500 Cedar Creek near Pleasant 10 74 4/30/2017 24.81 21,000 13.5% 7 9.6% 17.1% 9,880 8,640 11,300 17,500 15,200 20,000 23,200 20,100 26,800 31,400 26,700 36,900 37,900 31,600 45,500 44,900 36,600 55,000 52,400 41,900 65,500 61,900 48,000 79,900 View, Missouri 13 06919900 Sac River near Caplinger 6 43 4/30/2017 28.39 33,300 14.1% 7 8.7% 18.5% 15,300 11,900 19,300 27,900 22,200 36,500 37,500 29,400 52,000 50,700 38,600 77,600 61,000 44,900 101,000 71,700 50,600 130,000 82,800 55,900 163,000 97,900 62,200 217,000 Mills, Missouri5 14 06921070 Pomme de Terre River 3 49 4/30/2017 24.68 27,600 5.4% 18 2.9% 9.1% 13,400 11,900 15,100 19,800 17,600 22,200 23,900 20,900 27,200 28,900 24,900 33,500 32,600 27,600 38,600 36,400 30,100 43,900 40,300 32,700 49,500 45,300 35,800 57,300 near Polk, Missouri 15 06923500 Bennett Spring at Bennett 7 54 4/30/2017 7.46 4,010 9.4% 11 8.4% 17.0% 1,310 1,040 1,620 2,700 2,160 3,420 3,920 3,090 5,230 5,800 4,410 8,560 7,470 5,460 12,000 9,360 6,540 16,500 11,500 7,660 22,400 14,700 9,160 32,800 Springs, Missouri6 16 06927000 Maries River at 6 63 4/30/2017 21.00 27,400 7.5% 13 5.9% 12.8% 12,800 11,400 14,300 19,800 17,600 22,400 24,900 21,600 28,600 31,500 26,700 37,100 36,700 30,400 44,300 41,900 34,000 51,800 47,400 37,600 59,700 54,900 42,000 71,700 Westphalia, Missouri 17 06928000 Gasconade River near 1 73 4/30/2017 39.74 119,000 1.4% 73 0.2% 2.4% 25,000 21,300 29,400 48,000 41,200 56,000 65,600 56,000 76,900 89,500 74,800 107,000 108,000 87,900 132,000 126,000 100,000 158,000 145,000 113,000 186,000 170,000 128,000 226,000 Hazelgreen, Missouri 18 06930000 Big Piney River near Big 1 88 4/30/2017 30.67 90,200 0.22% 453 0.2% 2.0% 13,300 11,500 15,400 25,100 21,700 29,000 34,300 29,300 40,200 47,000 39,200 56,400 57,000 46,400 70,000 67,100 53,300 84,400 77,300 60,100 99,300 91,300 68,500 122,000 Piney, Missouri 19 06933500 Gasconade River at 1 99 5/1/2017 35.06 197,000 0.47% 215 0.2% 1.8% 30,400 26,800 34,400 57,100 50,500 64,500 78,700 68,700 90,100 110,000 94,000 130,000 137,000 113,000 165,000 164,000 132,000 203,000 193,000 153,000 244,000 232,000 177,000 304,000 Jerome, Missouri 20 06934000 Gasconade River near 1 78 5/2/2017 37.46 190,000 0.54% 186 0.2% 2.3% 34,000 29,800 38,900 61,400 53,800 70,000 82,900 71,800 95,700 114,000 96,400 134,000 139,000 115,000 167,000 165,000 133,000 203,000 192,000 152,000 242,000 229,000 175,000 299,000 Rich Fountain, Missouri 21 07010350 Meramec River at Cook 3 26 4/30/2017 16.90 26,200 5.7% 17 5.5% 16.7% 6,750 4,980 9,150 14,500 11,100 19,000 20,700 15,700 27,300 28,800 21,700 38,300 35,100 26,000 47,300 41,200 30,200 56,300 47,300 34,300 65,400 55,900 39,100 79,800 Station, Missouri Temporal Changes in Annual Peak Streamflows 21

Table 3. Estimated annual exceedance probability of the 2017 flood peaks and weighted peak streamflow estimates for selected flood Table 3. Estimated annual exceedance probability of the 2017 flood peaks and weighted peak streamflow estimates for selected flood quantiles at 59 U.S. Geological Survey streamgages included in this study. quantiles at 59 U.S. Geological Survey streamgages included in this study.—Continued

[ID, identifier; USGS, U.S. Geological Survey; AEP, annual exceedance probability; ft, foot; ft3/s, cubic foot per second; %, percent; --, not calculated; stations [ID, identifier; USGS, U.S. Geological Survey; ft, foot; ft3/s, cubic foot per second; AEP, annual exceedance probability; %, percent; --, not calculated; stations with peak of record during April–May 2017 flood are shown with rank value of “1” in bold] with peak of record during April–May 2017 flood are shown with rank value of “1” in bold]

[ID, identifier; USGS, U.S. Geological Survey; ft, foot; ft3/s, cubic foot per second; AEP, annual exceedance probability; %, percent; --, not calculated; stations with peak of record during April–May 2017 flood are shown with rank value of “1” in bold]

22 07013000 Meramec River near 1 102 4/30/2017 28.71 62,200 2.0% 49 0.2% 1.7% 15,400 13,600 17,400 28,100 24,700 32,100 38,000 32,900 43,800 51,600 43,800 60,900 62,400 51,700 75,400 73,600 59,500 91,000 85,200 67,300 108,000 101,000 76,800 132,000 Steelville, Missouri 23 07014500 Meramec River near 1 87 4/30/2017 36.38 95,300 1.2% 84 0.2% 2.0% 21,600 19,000 24,500 38,100 33,600 43,300 50,800 44,200 58,400 68,700 58,600 80,600 83,000 69,400 99,300 98,400 80,400 120,000 115,000 92,000 144,000 136,000 105,000 176,000 Sullivan, Missouri 24 07016500 Bourbeuse River at 5 104 5/2/2017 29.38 43,800 3.2% 31 2.8% 6.7% 15,200 13,900 16,700 24,200 22,000 26,700 31,100 27,700 34,900 40,800 35,400 46,900 48,600 41,300 57,100 56,900 47,300 68,400 65,800 53,500 80,900 77,900 61,300 99,000 Union, Missouri 25 07018100 Big River near 1 68 4/30/2017 33.54 66,900 1.8% 55 0.3% 2.6% 18,800 16,400 21,500 32,200 28,200 36,700 41,900 36,400 48,200 54,900 46,700 64,600 65,000 54,200 77,900 75,200 61,400 92,200 85,800 68,600 107,000 99,800 77,100 129,000 Richwoods, Missouri 26 07018500 Big River at Byrnesville, 3 96 5/1/2017 30.09 62,600 1.6% 62 1.5% 4.7% 17,200 15,400 19,300 29,200 26,000 32,900 38,000 33,500 43,100 49,800 42,900 57,900 59,100 49,700 70,300 68,600 56,400 83,400 78,600 63,200 97,700 91,700 71,400 118,000 Missouri 27 07019000 Meramec River at Eureka, 2 100 5/2/2017 46.11 169,000 1.1% 87 0.7% 3.2% 40,800 36,700 45,400 69,100 61,800 77,200 90,500 80,200 102,000 121,000 105,000 140,000 146,000 124,000 173,000 173,000 143,000 210,000 202,000 163,000 251,000 240,000 188,000 308,000 Missouri 28 07021000 Castor River at Zalma, 3 88 4/30/2017 29.00 69,700 0.93% 107 1.6% 5.1% 11,900 10,300 13,800 23,700 20,300 27,600 33,400 28,200 39,500 47,000 38,600 57,300 57,700 46,200 72,200 68,400 53,400 87,600 78,900 60,300 103,000 94,100 69,300 128,000 Missouri3 29 07035800 St. Francis River near 2 29 4/30/2017 27.32 69,300 2.7% 37 2.5% 10.7% 23,900 19,800 28,900 39,300 32,600 47,400 49,700 40,600 60,900 62,900 50,300 78,600 73,100 57,200 93,300 83,100 63,800 108,000 93,300 70,400 124,000 108,000 78,500 148,000 Mill Creek, Missouri 30 07036100 St. Fancis River near 2 26 4/30/2017 33.42 110,000 0.50% 202 2.8% 11.9% 34,500 28,900 41,300 52,900 44,300 63,100 64,500 53,300 78,100 78,200 63,300 96,700 88,800 70,300 112,000 99,200 77,100 128,000 110,000 83,900 144,000 125,000 92,400 169,000 Saco, Missouri 31 07037500 St. Francis River near 3 96 4/30/2017 37.13 126,000 0.50% 191 1.5% 4.7% 33,800 30,700 37,400 53,300 48,000 59,200 67,100 59,700 75,300 84,900 73,700 97,800 98,700 83,900 116,000 113,000 93,600 135,000 127,000 103,000 156,000 146,000 115,000 186,000 Patterson, Missouri 32 07043500 Little River Ditch No. 1 10 69 5/1/2017 18.99 9,500 11.5% 9 10.3% 18.3% 6,430 5,970 6,940 8,500 7,890 9,160 9,690 8,910 10,500 11,000 9,970 12,100 11,900 10,600 13,200 12,600 11,200 14,300 13,300 11,600 15,400 14,300 12,100 16,800 near Morehouse, Missouri 33 07050700 James River near 4 63 4/30/2017 20.90 38,100 3.1% 32 3.4% 9.0% 12,500 10,800 14,400 21,300 18,400 24,600 27,500 23,500 32,100 35,500 29,900 42,100 41,600 34,400 50,200 47,600 38,700 58,600 53,700 42,900 67,300 62,000 48,000 80,100 Springfield, Missouri3 34 07052100 Wilson Creek near 6 29 4/29/2017 9.15 4,220 20.1% 5 13.0% 26.9% 2,920 2,550 3,340 4,220 3,700 4,820 5,180 4,490 5,980 6,480 5,510 7,620 7,640 6,370 9,160 8,800 7,200 10,800 ------11,800 9,210 15,100 Springfield, Missouri4 35 07052500 James River at Galena, 2 96 4/30/2017 35.97 82,800 1.5% 67 0.8% 3.3% 20,700 18,300 23,500 36,400 32,200 41,100 48,100 42,000 55,000 64,100 54,700 75,200 76,600 63,900 91,900 89,600 73,100 110,000 103,000 82,300 129,000 121,000 93,200 157,000 Missouri 36 07055607 Crooked Creek at Kelly 1 33 4/30/2017 31.87 95,200 0.70% 143 0.6% 5.3% 10,100 7,760 13,200 22,900 17,400 30,200 34,200 25,600 45,800 51,500 38,000 69,800 66,000 47,900 91,100 81,600 58,400 114,000 ------123,000 83,900 180,000 Crossing at Yellville, Arkansas 37 07057500 North Fork River near 1 73 4/29/2017 41.82 189,000 <0.20% >500 0.2% 2.4% 13,200 11,200 15,600 26,800 22,400 32,000 38,500 31,500 47,100 55,700 44,200 70,100 69,300 53,600 89,600 83,000 62,800 110,000 96,900 71,900 131,000 116,000 83,200 163,000 Tecumseh, Missouri 38 07058000 Bryant Creek near 1 63 4/29/2017 33.07 111,000 <0.20% >500 0.3% 2.8% 12,600 10,500 15,200 25,400 21,300 30,300 35,700 29,600 43,200 50,400 40,700 62,300 61,700 48,800 78,100 73,300 56,600 94,900 85,000 64,400 112,000 101,000 73,600 138,000 Tecumseh, Missouri 39 07061500 Black River near 3 55 4/30/2017 23.30 71,200 4.9% 20 2.6% 8.1% 23,100 11,800 27,200 41,300 33,100 53,200 55,200 44,900 79,000 74,500 57,000 136,000 89,900 65,900 212,000 106,000 74,700 311,000 123,000 83,200 422,000 147,000 94,400 613,000 Annapolis, Missouri5 40 07063000 Black River at Poplar 3 70 5/1/2017 21.96 29,700 37.1% 3 2.0% 6.4% 8,040 6,940 9,340 13,500 11,500 16,400 17,800 14,900 23,100 24,300 19,600 34,900 29,900 23,200 46,800 36,100 27,000 62,100 43,000 31,000 81,600 53,400 36,400 116,000 Bluff, Missouri5 41 07066000 Jacks Fork at Eminence, 1 96 4/30/2017 27.72 106,000 0.20% 500 0.2% 1.8% 12,600 10,700 14,800 25,700 22,000 30,100 35,900 30,300 42,500 49,400 40,900 59,600 59,700 48,400 73,500 69,700 55,400 87,700 79,400 61,800 102,000 93,000 69,900 124,000 Missouri 42 07067000 Current River at Van 1 106 4/30/2017 37.42 179,000 0.47% 213 0.2% 1.7% 27,800 24,300 31,700 53,400 46,600 61,200 73,900 63,700 85,600 103,000 86,800 123,000 127,000 104,000 154,000 151,000 121,000 189,000 176,000 138,000 225,000 209,000 158,000 277,000 Buren, Missouri 43 07068000 Current River at 1 101 5/1/2017 33.13 183,000 0.37% 274 0.2% 1.8% 28,300 24,500 32,700 55,300 48,100 63,700 76,000 65,300 88,400 104,000 87,900 124,000 126,000 104,000 153,000 148,000 119,000 183,000 170,000 134,000 216,000 200,000 152,000 262,000 Doniphan, Missouri Temporal Changes in Annual Peak Streamflows 23

44 07069000 Black River at 1 77 5/2/2017 28.95 105,000 1.0% 96 0.2% 2.3% 23,550 14,510 27,240 41,970 35,650 50,660 55,890 46,590 71,790 74,960 60,050 108,800 90,050 70,120 144,100 105,700 80,070 185,800 122,100 89,880 233,700 144,700 102,600 306,000 Pocahontas, Arkansas3 45 07071500 Eleven Point River near 1 97 4/30/2017 28.66 124,000 <0.20% >500 0.2% 1.8% 9,930 8,430 11,700 21,900 18,500 25,800 32,300 27,000 38,700 48,200 39,400 59,100 61,100 48,800 76,500 74,700 58,300 95,700 89,000 68,000 116,000 107,000 79,200 146,000 Bardley, Missouri 46 07072000 Eleven Point River near 1 86 5/1/2017 27.90 137,000 <0.20% >500 0.2% 2.1% 12,700 11,000 14,700 25,500 21,800 29,800 37,300 31,100 44,700 56,600 45,700 70,200 72,800 57,300 92,600 90,300 69,300 118,000 108,000 81,500 144,000 134,000 96,800 184,000 Ravenden Springs, Arkansas 47 07074420 Black River at Elgin 2 27 5/4/2017 33.99 173,000 0.83% 120 2.7% 11.5% 41,590 33,000 51,180 67,950 54,720 88,590 88,090 69,730 123,700 116,400 89,000 184,100 139,600 103,300 243,500 164,400 117,400 317,700 191,200 131,400 410,300 229,700 149,700 568,300 Ferry, Arkansas3 48 07076750 White River at 1 38 5/8/2017 31.50 200,000 1.1% 90 0.5% 4.6% 69,300 59,400 81,000 102,000 87,000 124,000 125,000 105,000 160,000 155,000 127,000 216,000 179,000 142,000 266,000 203,000 158,000 325,000 228,000 172,000 394,000 262,500 190,000 502,000 Georgetown, Arkansas5 49 07077000 White River at DeValls 2 47 5/10/2017 31.31 187,000 0.88% 114 2.1% 6.7% 71,900 63,600 80,800 101,000 89,200 115,000 120,000 106,000 141,000 145,000 125,000 179,000 164,000 138,000 212,000 183,000 151,000 248,000 202,000 163,000 289,000 227,000 178,000 350,000 Bluff, Arkansas5 50 07077555 Cache River near Cotton 1 31 5/5/2017 20.25 10,100 9.2% 11 0.6% 5.6% 6,790 6,080 7,590 8,750 7,930 9,660 9,920 8,820 11,200 11,300 9,730 13,100 12,200 10,300 14,500 13,100 10,800 16,000 ------15,100 11,800 19,400 Plant, Arkansas 51 07185765 Spring River at Carthage, 2 30 4/29/2017 18.44 30,400 8.2% 12 2.5% 10.4% 9,430 7,380 12,000 19,200 15,400 24,000 27,300 21,800 34,300 39,200 30,700 50,200 48,500 37,200 63,300 58,100 43,700 77,300 68,100 50,300 92,200 80,800 57,600 113,000 Missouri 52 07186000 Spring River near Waco, 8 95 4/30/2017 28.14 55,800 8.2% 12 5.6% 11.0% 20,000 17,600 22,800 37,100 32,500 42,300 50,500 43,600 58,500 69,900 58,900 83,000 85,600 70,400 104,000 102,000 82,100 127,000 120,000 94,300 152,000 143,000 108,000 188,000 Missouri 53 07187000 Shoal Creek above Joplin, 4 94 4/29/2017 22.96 52,900 2.8% 36 2.3% 6.1% 7,700 6,580 9,000 16,500 13,900 19,500 24,400 20,200 29,600 36,800 29,400 46,100 46,900 36,500 60,200 57,300 43,600 75,300 67,900 50,600 91,000 82,300 59,100 115,000 Missouri 54 07189000 Elk River near Tiff City, 2 78 4/29/2017 27.39 107,000 1.4% 70 0.9% 4.1% 22,200 18,700 26,400 43,400 37,000 51,000 59,600 49,600 71,500 81,200 65,900 100,000 98,000 77,900 123,000 114,000 89,200 147,000 132,000 101,000 172,000 154,000 114,000 208,000 Missouri3 55 07191220 Spavinaw Creek near 2 58 4/29/2017 16.94 19,900 6.5% 15 1.3% 5.5% 4,270 3,220 5,660 10,100 8,090 12,500 15,400 12,000 19,800 24,000 17,600 32,800 32,100 22,800 45,200 41,300 28,300 60,300 ------67,100 42,000 107,000 Sycamore, Oklahoma 56 07195500 Illinois River near Watts, 1 62 4/30/2017 30.12 128,000 0.31% 325 0.3% 2.8% 19,600 16,900 22,900 35,700 30,200 42,300 48,600 40,100 58,900 67,000 52,800 85,100 81,300 61,700 107,000 96,200 70,200 132,000 ------134,000 88,100 203,000 Oklahoma3 57 07196000 Flint Creek near Kansas, 3 58 4/29/2017 18.31 19,400 8.5% 12 2.4% 7.7% 4,170 3,230 5,370 10,800 8,450 13,800 17,200 13,300 22,300 27,700 20,300 37,800 37,100 26,300 52,300 48,000 32,700 70,400 ------79,200 48,400 130,000 Oklahoma3 58 07261000 Cadron Creek near Guy, 3 61 4/30/2017 23.57 18,000 7.6% 13 2.3% 7.3% 8,520 7,570 9,590 13,200 11,800 14,900 16,400 14,500 18,700 20,600 17,600 24,000 23,700 19,800 28,400 26,900 21,900 33,000 ------34,300 26,300 44,900 Arkansas 59 07359610 Caddo River near Caddo 3 29 4/30/2017 23.32 35,800 13.6% 7 4.9% 15.0% 19,400 16,300 23,000 30,900 25,800 37,000 38,900 31,700 47,800 49,400 38,800 63,000 57,300 43,600 75,200 65,400 48,200 88,800 ------85,000 58,100 125,000 Gap, Arkansas

166.7% confidence intervals for observed AEP are determined nonparametrically. In some instances, the nonparametric results place bounds outside the estimate, making these confidence intervals nonsensical. 295% confidence limits or 90% confidence intervals (both imply 5% tails). 3Streamflow affected to unknown degree by regulation or diversion. 4Streamflow affected by urbanization. 5Streamflow affected by regulation or diversion. Flood frequency analysis was conducted using only regulated period of record and at-site estimates of peak streamflows without weighting with rural regression equation estimates. 6Site is a spring. Expected peak streamflows were determined using only at-site estimates of peak streamflows without weighting with rural regression equation estimates. Temporal Changes in Annual Peak Streamflows 25

98° 96° 94° 92° 90° 88° 86°

Iowa Nebraska Illinois Ohio

40° Missouri Indiana

7 8 4 27 24 20 Kansas 9 26 5 1 16 19 22 25 6 38° 13 17 23 12 14 21 29 2 11 15 39 31 3 Kentucky 52 18 41 28 51 10 33 34 4230 32 53 35 40 37 38 45 43 54 55 36 46 44 36° 57 56 47 Tennessee 48 Oklahoma 58 50 49 Georgia 59

34° Mississippi Alabama Arkansas

Texas Louisiana 32°

Base from U.S. Geological Survey, 1:2,000,000-scale data, 2005 0 50 100 MILES Albers Equal-Area Projection North American Datum of 1983 (NAD83) 0 50 100 KILOMETERS EXPLANATION Flood annual exceedance probability (AEP) Mississippi in percent-- Number is map identifier (table 3)

Greater than 10 4.1 to 10 2.1 to 4.0 1.1 to 2.0 0.21 to 1.0 Less than 0.2

Figure 10. Spatial distribution of the magnitude of annual exceedance probabilities of peak streamflows at 59 U.S. Geological Survey streamgages for the April–May 2017 flood. Temporal Changes in Annual Peak Streamflows 27

98° 96° 94° 92° 90° 88° 86° A. Illinois Indiana 39° Missouri 24 27 Kansas #20 # ## # # 23 26 38° 17 #19 # # 22 18 #3 41 31 52 42 # #28 Kentucky # # # 37° Ó #35 53 45 # #43 46#

36° Tennessee Oklahoma

35° Arkansas 0 50 100 MILES 1930 2017

34° 0 50 100 KILOMETERS Texas Mississippi Alabama

98° 96° 94° 92° 90° 88° 86° Illinois B. 7 # Indiana 39° Missouri 9 24 27 Kansas ###16 # ## 20 # # 26 # 25 6 38° 17 #19 23 # #12 # # 22 18 3 31 28 # 52 41 Kentucky 33 42# # # # 32 #53 37° 45 # #35 38 43 #54 ##37 # # # 57 46 ## Tennessee 36° 56 Oklahoma 58 Ó

35° Arkansas 1956 2017

34° Texas Mississippi Alabama Base from U.S. Geological Survey, 1:2,000,000-scale data, 2005 Albers Equal-Area Projection EXPLANATION North American Datum of 1983 (NAD83) Study area Percent change of the median annual peak streamﬂow per year and map ID (see table 1) Not all ranges are represented on map Positive Negative No change 12 12 12 # 12 12 0.10 to 2.0 # 4.01 to 6.0 # 8.01 to 10.0 Ó -0.13 to -0.10 -0.099 to 0.099 12 12 # 2.01 to 4.0 # 6.01 to 8.0

Figure 11. Percentage changes in median annual peak streamflow values for selected U.S. Geological Survey streamgages for A, 1930–2017; B, 1956–2017; C, 1975–2017; and D, 1989–2017. 28 Flooding in the Southern Midwestern United States, April–May 2017

98° 96° 94° 92° 90° 88° 86°

C. 7 Illinois # 4 Indiana 39° Missouri # 9 24 27 Kansas #16 # # ##20 # # 5 1 23 26 # # # 6 19 # 2 38° 17 # 25 #12 14 15 22 ## # ## #18 10 31 # 3 52 # 41 28 # 33 # 42# # Kentucky ##53 ##34 32 37° 51 45 43 # #35 38 #54 ##37 # #46 # #57 55 ##56 36° Tennessee Oklahoma #58

35° Arkansas 0 50 100 MILES 1975 2017

34° 0 50 100 KILOMETERS Texas Mississippi Alabama

98° 96° 94° 92° 90° 88° 86°

D. 7 Illinois # Indiana 39° Missouri # 4 9 24 Kansas 16 27 ## # 1 #20 26# 5 # 23# #25 12 17 19 # 6 38° 15 # 22 # 14 29 ## ###18 2 10 30 # 52 33 41 # #3 34 # 28 Kentucky # 53 # # 42 # # # # 31 32 37° # 51 # #35 38 37 45 43 54 # # # # # # #57 36# 46 55## 56 36° Tennessee Oklahoma #58 #50 35° Arkansas 1989 2017 59

Figure 11. Percentage changes in median annual peak streamflow values for selected U.S. Geological Survey streamgages for A, 1930–2017; B, 1956–2017; C, 1975–2017; and D, 1989–2017.—Continued Temporal Changes in Annual Peak Streamflows 29

96° 94° 92° 90° 88° 96° 94° 92° 90° 88°

A 2301 1106 B 2301 1106 39° 2302 Illinois 39° 2302 Illinois Indiana Indiana Kansas 2303 1108 1207 Kansas 2303 1108 1207 1109 1109 38° Missouri 38° Missouri 2305 2305 Kentucky Kentucky 37° 2304 37° 2304 2306 2306 3403 3403 301 301 36° 302 303 Tennessee 36° 302 303 Tennessee 3406 3406 304 304 35° 35° 305 306 305 306 Oklahoma Oklahoma 34° Mississippi 34° Mississippi 307 Alabama 307 Alabama Texas Arkansas Texas Arkansas

1930–2016 1956–2016

96° 94° 92° 90° 88° 96° 94° 92° 90° 88°

C 2301 1106 D 2301 1106 39° 2302 Illinois 39° 2302 Illinois Indiana Indiana Kansas 2303 1108 1207 Kansas 2303 1108 1207 1109 1109 38° Missouri 38° Missouri 2305 2305 Kentucky Kentucky 37° 2304 37° 2304 2306 2306 3403 3403 301 303 301 303 36° 302 Tennessee 36° 302 Tennessee 3406 3406 304 304 35° 35° 305 306 305 306 Oklahoma Oklahoma Mississippi Mississippi 34° 307 34° 307 Alabama Alabama Texas Arkansas Texas Arkansas Base from U.S. Geological Survey, 0 50 100 MILES 1:2,000,000-scale data, 2005 1975–2016 1989–2016 Albers Equal-Area Projection North American Datum of 1983 (NAD83) 0 50 100 KILOMETERS

EXPLANATION Flood study area Climate division and identifier Percent change of the median annual precipitation, per year 301 Positive change, 0.1 to 0.62

301 No change, -0.099 to +0.099

301 Negative change -0.1 to -0.9

Figure 12. Percentage change in the median annual precipitation by climate division within the study area for A, 1930–2016; B, 1956–2016; C, 1975–2016; and D, 1989–2016. 30 Flooding in the Southern Midwestern United States, April–May 2017

Values are averages Values are averages from 16 long-term from 22 long-term stations stations Number of events with Number of events Number of events with Number of events precipitation greater than 2 inches greater precipitation precipitation greater than 2 inches greater precipitation

Values are averages Values are averages from 28 long-term from 43 long-term stations stations Number of events with Number of events Number of events with Number of events precipitation greater than 2 inches greater precipitation precipitation greater than 2 inches greater precipitation

Values are averages from 21 long-term stations

Long-term average Number of events with Number of events precipitation greater than 2 inches greater precipitation

Years

Figure 13. Change in frequency of daily high intensity (greater than 2–3 in.) precipitation from the long-term (1900–2014) average, by state. References Cited 31

Summary Cohn, T.A., Lane, W.L., and Baier, W.G., 1997, An algorithm for computing moments-based flood quantile estimates Excessive rainfall resulted in flooding on numerous rivers when historical flood information is available: Water throughout the southern Midwestern United States in late Resources Research, v. 33, no. 9, p. 2089–2096. April and early May of 2017. Tropical moisture lifted over a England, J.F. Jr., Cohn, T.A., Faber, B.A., Stedinger, J.R., stalled frontal system caused heavy rains from Texas to Ohio Thomas, W.O., Veilleux, A.G., Kiang, J.E., and Mason, between April 28 and May 10, resulting in extensive flood- R.R., 2017, Guidelines for determining flood flow fre- ing from eastern Oklahoma to southern Indiana including quency, Bulletin 17C: U.S. Geological Survey Techniques parts of Missouri, Arkansas, and Illinois. The heaviest rainfall and Methods book 4, chap. 5, 228 p. amounts during April 28–30 occurred over extreme northeast Oklahoma and northern Arkansas, across the southern half of Federal Emergency Management Agency [FEMA], Missouri, southern Illinois, and southern Indiana, and included 2017a, President Donald J. Trump approves Arkan- totals of 6 to 10 inches with some isolated higher amounts. sas disaster declaration, accessed July 7, 2017, at Peak-of-record streamflows were set at 21 U.S. Geologi- https://www.fema.gov/news-release/2017/06/15/president- cal Survey streamgages in the southern Midwest during the donald-j-trump-approves-arkansas-disaster-declaration. resulting April May 2017 flooding. Each of the five states Federal Emergency Management Agency [FEMA], 2017b, included in the study area had at least one streamgage with a President Trump approves major disaster declara- peak of record during the flood. The annual exceedance prob- tion for State of Oklahoma: accessed July 7, 2017, at ability (AEP) estimates for the April May 2017 flood peak https://www.fema.gov/news-release/2017/05/26/president- streamflows indicate that peaks at 5 USGS streamgages had an trump-approves-major-disaster-declaration-state-oklahoma. AEP of 0.2 percent or less, and peak streamflows at 15 USGS streamgages had an AEP in the range from greater than 0.2 to Flynn, K.M., Kirby, W.H., and Hummel, P.R., 2006, User’s 1 percent. manual for program PeakFQ, Annual flood frequency analy- Examination of the magnitude of the temporal changes sis using Bulletin 17B guidelines: U.S. Geological Survey in median annual peak streamflows indicated positive Techniques and Methods, book 4, chap. B4, 42 p. increases, in general, throughout the study area for each of the 1930–2017, 1956–2017, 1975–2017, and 1989–2017 analysis Frankson, R., Kunkel, K., Champion, S., and Stewart, B., 2017a, Missouri State Summary: NOAA Technical Report periods. The median increase in peak streamflows was great- NESDIS 149-MO, 4 p. accessed October 24, 2017, at est in the 1975–2017 and 1989–2017 periods with maximum https://statesummaries.ncics.org/mo. increases of 8–10 percent per year. No stations in either the 1975–2017 or 1989–2017 analysis period had median negative Frankson, R., Kunkel, K., Champion, S., Stewart, B., changes in peak streamflows. Easterling, D., Hall, B., and Angel, J.R., 2017b, Illi- A primary driver of change in peak streamflows is nois State Summary: NOAA Technical Report NES- precipitation, but the changes in annual precipitation provided DIS 149-IL, 4 p., accessed October 24, 2017, at little explanation for the substantial increase in the magnitude https://statesummaries.ncics.org/il. of streamflow peaks in the 1989–2017 analysis period. The increase in the magnitude of the positive changes in annual Frankson, R., Kunkel, K., Champion, S., Stewart, B., and peak streamflows during this period likely is better explained Runkle, J., 2017c, Indiana State Summary: NOAA Tech- by a change in the frequency of larger magnitude rain events nical Report NESDIS 149-IN, 4 p. accessed October 24, (greater than 2 or 3 inches) with time. 2017, at https://statesummaries.ncics.org/in. Frankson, R., Kunkel, K., Stevens, L., Champion, S., and Stewart, B., 2017d, Oklahoma State Summary: NOAA References Cited Technical Report NESDIS 149-OK, 4 p. accessed Octo- ber 24, 2017, at https://statesummaries.ncics.org/ok. Cable News Network, 2017, Aerial images show devastat- Holmes, R.R., Jr., Koenig, T.A., and Karstensen, K.A., 2010, ing flooding in central US: Cable News Network web page Flooding in the United States Midwest, 2008: U.S. Geologi- accessed July 5, 2017, at http://www.cnn.com/2017/05/04/ cal Survey Professional Paper 1775, 64 p. weather/missouri-flooding-images/. Holmes, R.R., Jr., Koenig, T.A., Rydlund, P.H., and Heimann, Cohn, T.A., England, J.F., Berenbrock, C.E., Mason, R.R., D.C., 2016, Examination of flood characteristics at selected Stedinger, J.R., and Lamontagne, J.R., 2013, A generalized streamgages in the Meramec River Basin, Eastern Missouri, Grubbs-Beck test statistic for detecting multiple potentially December 2015–January 2016: U.S. Geological Survey influential low outliers in flood series: Water Resources Open-File Report 2016–1140, 7 p., https://doi.org/10.3133/ Research, v. 49, no. 8, p. 5047–5058. ofr20161140. 32 Flooding in the Southern Midwestern United States, April–May 2017

Interagency Advisory Committee on Water Data, 1982, Office of Missouri Governor, 2017, At Governor Greiten’s Guidelines for determining flood flow frequency (revised): request, President Trump declares major disaster in Mis- U.S. Geological Survey, Office of Water Data Coordination, souri: Office of Missouri Governor web page, accessed Bulletin 17B, 28 p., 14 app., and 1 pl. July 7, 2017, at https://governor.mo.gov/news/archive/ governor-greitens%E2%80%99-request-president-trump- Jennings, M.E., Thomas, T.O., Jr., and Riggs, H.C., 1994, declares-major-disaster-missouri. Nationwide summary of U.S. Geological Survey regional regression equations estimating magnitude and frequency of Parrett, Charles, Melcher, N.B., and James, R.W., Jr., 1993, floods for ungaged sites: U.S. Geological Survey Water- Flood streamflows in the upper Mississippi River basin, Resources Investigations Report 94–4002, 196 p. 1993: U.S. Geological Survey Circular 1120–A, 14 p. Langbein, W.B., and Iseri, K.T., 1960, General introduction Runkle, J., Kunkel, K., Champion, S., Stewart, B., and Easter- and hydrologic definitions: U.S. Geological Survey Water- ling, D., 2017, Arkansas State Summary: NOAA Technical Supply Paper 1541-A, 29 p. Report NESDIS 149–AR, 4 p. accessed October 24, 2017, Lewis, J.M., 2010, Methods for estimating the magnitude and at https://statesummaries.ncics.org/ar. frequency of peak streamflows for unregulated streams in Salmi, T., Määttä, A., Anttila, P., Ruoho-Airola, T., and Oklahoma: U.S. Geological Survey Scientific Investigations Amnell, T., 2002, Detecting trends of annual values of Report 2010–5137, 41 p. atmospheric pollutants by the Mann-Kendall test and Missouri Department of Public Safety, State Emergency Sen’s slope estimates—The excel template application Management Agency, 2017, More Missouri residents and MAKESENS: Helsinki, Finland, Finnish Meteorological local governments will receive federal disaster assistance Institute Report 31, 35 p. accessed September 12, 2017, at after FEMA approves Gov. Greiten’s request to expand http://en.ilmatieteenlaitos.fi/makesens. Missouri disaster declaration: Missouri Department Sauer, V.B., and Fulford, J.M., 1983, Floods of December of Public Safety web page, accessed July 23, 2017, at 1982 and January 1983 in central and southern Mississippi https://sema.dps.mo.gov/news/newsitem/uuid/5e3948b0- River Basin: U.S. Geological Survey Open-File Report 4416-4763-bb4b-0f4445565a20. 83–213, 41 p. National Centers for Environmental Prediction, 2017, Sur- Sen, P.K., 1968, Estimates of the regression coefficient based face Weather Maps, April 27–30, 2017: National Centers on Kendall’s tau: Journal of American Statistical Associa- for Environmental Prediction web page, accessed June 17, tion, v. 63, p. 1379–1389. 2017, at http://www.ncep.noaa.gov/. Soong, D.T., Ishii, A.L., Sharpe, J.B., and Avery, C.F., 2004, National Oceanic and Atmospheric Administration (NOAA), Estimating flood-peak streamflow magnitudes and frequen- National Centers for Environmental Information, cies for rural streams in Illinois: U.S. Geological Survey 2017a, Data access: National Centers for Environmen- Scientific Investigations Report 2004–5103, 147 p. tal Information web page, accessed August 2, 2017, at https://www.ncdc.noaa.gov/data-access. Southard, R.E., 2010, Estimating the magnitude and frequency of floods in urban basins in Missouri: U.S. Geological Sur- National Oceanic and Atmospheric Administration (NOAA), vey Scientific Investigations Report 2010–5073, 27 p. National Centers for Environmental Information, 2017b, National Climate Report: National Centers for Environ- Southard, R.E., and Veilleux, A.G., 2014, Methods for estimat- mental Information web page, accessed August 2, 2017, at ing annual exceedance-probability discharges and largest https://www.ncdc.noaa.gov/sotc/national/. recorded floods for unregulated streams in rural Missouri: U.S. Geological Survey Scientific Investigations Report National Oceanic and Atmospheric Administration (NOAA), 2014–5165, 39 p., https://doi.org/10.3133/sir20145165. National Centers for Environmental Information, 2017c, U.S. Climate Divisions: National Centers for Environ- U.S. Geological Survey, 2017a, National Water Informa- mental Information web page, accessed June 27, 2017, at tion System—Web interface: accessed June 30, 2017, at https://www.ncdc.noaa.gov/monitoring-references/maps/ https://doi.org/10.5066/F7P55KJN. us-climate-divisions.php. U.S. Geological Survey, 2017b, WaterWatch, Flood—Flood National Weather Service, 2017a, National Weather Service Table Builder: U.S. Geological Survey, accessed on July 5, glossary: National Weather Service web page, accessed 2017, at https://waterwatch.usgs.gov/. October 23, 2017, at http://w1.weather.gov/glossary/. Veilleux, A.G., Cohn, T.A., Flynn, K.M., Mason, R.R., and National Weather Service, 2017b, 28-30 April His- Hummel, P.R., 2013, Estimating magnitude and frequency toric Flooding Event, Springfield, Missouri, Fore- of floods using the PeakFQ 7.0 program: U.S. Geological cast Office: National Weather Service web page, Survey Fact Sheet 2013–3108, 2 p. accessed June 17, 2017, at https://www.weather.gov/ sgf/28-30AprilHistoricFloodingEvent. References Cited 33

Wagner, D.M., Krieger, J.D., and Veilleux, A.G., 2016, Methods for estimating annual exceedance probability discharges for streams in Arkansas, based on data through water year 2013: U.S. Geological Survey Scientific Investi- gations Report 2016–5081, 136 p., https://doi.org/10.3133/ sir20165081.

Gasconade River near Rich Fountain, Mo., May 1, 2017. Photograph by Larry Buschmann, USGS. Above: USGS hydrologist tethering acoustic Doppler current profiler (ADCP), Black River near Poplar Bluff, Mo., May 1, 2017. Photograph by Chris Rowden, USGS. Glossary 35

Glossary

Note: Glossary definitions are from Langbein and Iseri (1960), Holmes and others (2010), and National Weather Service (2017a). annual exceedance probability (AEP) The low flows (PILFs), and uncertain data points probability, or chance, of a flood of a given while also providing enhanced confidence streamflow magnitude being equaled or intervals on the estimated peak streamflows. exceeded in any given year. The probability flood An overflow or inundation that comes can be expressed as a fraction, decimal, or from a river or other body of water, and percentage. causes or threatens damage. annual exceedance probability flood quantile flood peak The highest value of the stage (AEP flood quantile) The value of the peak or streamflow attained by a flood; often streamflow that corresponds to a particular designated as peak stage or peak streamflow annual exceedance probability (for example, respectively. 1-percent AEP flood quantile) flood quantile See “annual exceedance Bulletin 17B Report by the Interagency probability flood quantile.” Advisory Committee on Water Data (1982) flood stage The stage at which overflow of that delineates the recommended method for the natural banks of a stream begins to cause flood-probability analysis in the United States. damage in the reach in which the water sur- Bulletin17C Report published by the U.S. face elevation is measured. Geological Survey in 2017 representing the hydrograph A graph showing stage, stream- efforts of the Advisory Committee on Water flow, velocity, or other property of water with Information, that updates the methods for respect to time. flood-probability analysis in the United States presented in Bulletin 17B. log-Pearson Type III probability distribution One of the family of probability confidence limits To gauge the accuracy distributions developed by Karl Pearson that of an approximation based on a probability is used in the United States as a best-fit for the distribution, upper and lower confidence distribution of annual peak flood streamflows limits can be estimated based on the proper- in the Bulletin 17B analysis procedures devel- ties of the probability distribution. This report oped by the Interagency Advisory Committee includes the 95-percent confidence limits of on Water Data (1982). the estimate of the flood quantiles as com- peak-of-record streamflow The largest puted by the methods outlined in Bulletin instantaneous streamflow value for the period 17B. that data have been collected. discharge In its simplest concept discharge peak stage See “flood peak.” means outflow; therefore, the use of this term is not restricted as to course or location, and peak streamflow See “flood peak.” it can be applied to describe the flow of water precipitation As used in hydrology, precipi- from a pipe or from a drainage basin. tation is the discharge of water, in liquid or expected moment algorithm The expected solid state, out of the atmosphere, generally moment algorithm (EMA) is an updated upon a land or water surface. It is the common method for fitting the log pearson type III process by which atmospheric water becomes probability distribution that is a more effec- surface or subsurface water. The term “precip- tive means of incorporating historical peak itation” also is commonly used to designate streamflow information into a flood-frequency the quantity of water that is precipitated. analysis than the previous Bulletin 17B probability A means to express the likeli- method. The EMA can accommodate interval hood of something occurring, also known as data, which simplifies analysis of datasets chance. The probability can be expressed as a containing historic data, potentially influential fraction, decimal, or percentage. 36 Flooding in the Southern Midwestern United States, April–May 2017

probability distribution Describes the range Sen’s slope estimate A nonparametric of possible values that a random variable can estimate of trend based on the median slope of attain and the probability that the value of the data pairs in a time series. random variable is within any subset of that stage Height of a water surface above an range. established datum, also known as gage height. recurrence interval The average interval of stationary front A front between warm and time within which the given flood is expected cold air masses that is moving very slowly or to be equaled or exceeded once. not at all. regional regression equation (RRE) Equa- streamflow The discharge that occurs in a tion developed through use of regression natural channel. Although the term discharge techniques that relate the flood-probability can be applied to flow in a canal, the word data at many streamgages in a region to the streamflow uniquely describes the discharge basin characteristics of the streams monitored in a surface stream course. The units of mea- by the streamgages. For any location along a surement often are reported in cubic feet per stream, a user can enter the basin characteris- second (ft3/s). tics (drainage area, basin slope, and so forth) as independent variables into the equations streamgage A particular site on a stream and compute various flow characteristics where a record of streamflow is obtained. (for example, 1-percent AEP flood quantile, trend The change of a particular variable 2-percent AEP flood quantile, and annual with either time or spatial location as com- mean streamflow). puted by statistical analysis.

Spavinaw Creek near Sycamore, Okla., April 29, 2017. Photograph by U.S. Geological Survey.

For more information about this publication, contact Director, USGS Missouri Water Science Center 1400 Independence Road Rolla, MO 65401 (573) 308–3667

For additional information visit https://mo.water.usgs.gov

Publishing support provided by the Rolla Publishing Service Center Back cover. USGS hydrologic technician wading St. Francis River near Patterson, Mo., April 30, 2017. Photograph by Josh Keele, USGS. Heimann and others—Flooding in the Southern Midwestern United States, April–May 2017—Open-File Report 2018–1004 ISSN 2331-1258 (online) https://doi.org/10.3133/ofr20181004