The floods

THE RIVER IN FLOOD

A power river is a flood river, and Mishawaka's flood record is best read in the gauge record of the river itself: The documented great floods of the St. Joseph at this reach are a snowmelt river's floods. In March 1982 the rapid melting of a snowpack holding two to six inches of water, coinciding with moderate rain, flooded the whole northern tier of Indiana; the U.S. Geological Survey's report on that flood (Water-Resources Investigations Report 83-4201) assigns the St. Joseph River's flooding a recurrence interval of about fifty years, and high-water marks surveyed from March 1982 still calibrate the federal flood studies of this reach — the USGS's flood-inundation mapping for the river at Elkhart was fitted to the documented 1982 marks. At the South Bend gauge, four miles below the Mishawaka dam, the 1982 crest of 10.9 feet stood as the record until February 2018. Downstream at Niles, Michigan — the same river, printed here as river context and as nothing else — the standing record before 2018 was the crest of 15.10 feet on 5 April 1950.

The flood of February 2018 is the fullest documented in the record. Nearly thirty inches of snow had fallen by 17 February; then the month's rain set all-time February records — more than eight inches for the month against a previous record near five — including 3.75 inches on 20 February alone, as the temperature rose above sixty degrees and the snowpack let go. The river crested at South Bend at a historic 12.7 feet on 22 February, with a peak flow of 25,300 cubic feet per second measured at the Niles gauge — some fourteen and a half billion gallons a day passing down the river — and at Niles it crested at 17.33 feet, more than two feet above the 1950 record. For Mishawaka's own part, the contemporary record in hand is plain but general: the mayor of neighboring Warsaw, writing to his own city on 2 March 2018, recorded that "South Bend and Mishawaka suffered similar flooding of the Saint Joe River," and the county emergency figures given out that March counted about 700 homes affected in St. Joseph County, 65 of them with major damage — county figures, not a Mishawaka tally. An earlier modern flood, in August 2016, sent five and a half billion gallons a day through the South Bend reach on the county's accounting. What the floods took in Mishawaka itself — street by street, house by house, in 1913, in 1982 and in 2018 — is not established in the sources: the city's commissioned history as extracted carries no flood narrative, and the settling sources are the South Bend Tribune's flood coverage in those years, the city's council minutes, and the USGS peak-flow files for the river's gauges.

Sources:

1. U.S. Geological Survey, Floods of March 1982, Indiana, Michigan, and Ohio (WRIR 83-4201, 1984) — the snowmelt flood; the St. Joseph River's recurrence interval of about fifty years.
2. U.S. Geological Survey, flood-inundation study for the St. Joseph River at Elkhart — calibration to the documented high-water marks of March 1982.
3. City of South Bend, flood-study testimony (Lawson-Fisher, August 2018) — the February 2018 snow and rain figures; the 12.7-foot crest of 22 February; the 25,300 cfs peak at Niles; the prior 10.9-foot record of 1982.
4. National Weather Service, Northern Indiana — the Niles crest of 17.33 feet on 22 February 2018 against the previous record of 15.10 feet, 5 April 1950.
5. Mayor's letter, City of Warsaw, 2 March 2018 — South Bend and Mishawaka's similar flooding of the St. Joseph River.
6. St. Joseph County emergency management figures, March 2018 — some 700 county homes affected, 65 with major damage (county-wide).