The river's record, and February 2018 · the crest that broke it

2018, against the gauge's whole record

South Bend is a river city in the literal sense — the town exists because the river bends — and in February 2018 the river made its largest statement in the gauge era: The month began as the snowiest February start on record at the South Bend cooperative observer, laying down the snowpack; then, between 19 and 21 February, a warm, saturated air mass dropped four to six inches and more of rain across northern Indiana on the melting snow. At South Bend the Weather Service measured 5.61 inches of rain in the event — more than twice the previous rainfall for any February, and, as the Service's senior meteorologist put it, the heaviest three-day rainfall for any month since records began in the early 1900s; 3.75 inches of it fell on 20 February alone, a single-day record.

On 22 February 2018 the St. Joseph River crested at South Bend at 12.7 feet — the historic peak in the city's own flood record, presented to the Common Council in the city's 2018 sewer and flood study; the United States Geological Survey's gauge at Niles showed a peak flow of 25,300 cubic feet per second, 14.5 billion gallons a day passing through the city at the flood's worst. Indiana's governor issued a disaster declaration for nine northern Indiana counties. Unlike the broad floods of memory, this one, in the city study's words, "manifested itself in just a few neighborhoods" — the riverfront districts built in the floodplain took it, and took it at a level the study's engineers placed beyond the five-hundred-year flood in flow terms. The systematic crest table against which 2018 stands — the Weather Service's historic-crests list for the South Bend gauge — is named here as the record of the river's earlier floods; this section prints the 2018 crest from the city's study and the gauge, and carries the full crest series as an assembly pull rather than reconstruct it from fragments.

Sources:

1. City of South Bend, Health and Public Safety Committee presentation, 20 August 2018 (Lawson Fisher Associates, 2018 South Bend Sewer & Flood Study findings; city document) — the historic crest of 12.7 feet, the USGS peak flow of 25,300 cfs at the Niles gauge, the February rainfall records (3.75 in. on 20 February), and the flood's concentration in a few neighborhoods.
2. National Weather Service, Northern Indiana, and Lashley's retrospective as reported in the Goshen News, February 2019 — the 5.61 inches at South Bend, the three-day rainfall record since the early 1900s, and the event's mechanics; American Meteorological Society, 99th Annual Meeting (Paper 354237) — the record snowy February start at the South Bend cooperative observer, the 19–21 February rains, and the governor's nine-county disaster declaration.