There’s a lot of water flowing through southern Manitoba right now. In the middle of April, government officials warned that the province was experiencing an exceptional flood in terms of the total area affected. By the first weeks of May, the situation along the Assiniboine River became a crisis as officials coped with what they termed, in effort to underline the severity of the situation, a flood with a 300-year recurrence interval. 
Clearly, this is a major inundation. A lot of land is underwater, and a lot of people are suffering. But is the flood of 2011 really, as has been repeatedly stated, “without precedent”?  This is a big claim, and it merits further consideration.
Is this a flood without precedent? Well, probably not. As geographer W.F. Rannie determined, historic records indicate the presence of significant Assiniboine River flooding in 1861, 1856, 1854, 1852, 1851, 1850, 1849, 1831, 1830, 1829, 1826, 1825, 1812, 1810, 1801, 1797, and 1795.  Studying tree growth, which is affected by flooding, has allowed scientists to determine there were likely large-scale Assiniboine River floods even earlier, in 1788, 1700, 1675, 1597, 1553, 1538, 1510 and 1496.  Neither historic nor tree ring records allow us to estimate the extremity of any given inundation, but it is at least possible that some of these floods approached the levels today being seen along the Assiniboine.
It may be more accurate to argue that this is a flood without precedent since extensive agricultural and urban settlement in the Province of Manitoba. But even allowing this, the potential of the Assiniboine River to flood in a catastrophic manner has long been recognized. The first federal government investigation of flooding along the Assiniboine took place in 1886-87, just over 15 years after the province of Manitoba was created in 1870. Between 1913 and 1920, nearly $22,000 was spent building and improving dykes between Portage La Prairie and Winnipeg.  And the protective work has continued since that time. So a flood unequaled since extensive settlement, perhaps; but unforeseen, certainly not.
And many of the actions being taken to combat the 2011 flood are in themselves well-precedented. There is currently much anxiety, both among government officials and affected residents, about the decision to deliberately cut a road embankment at a location (the now-infamous Hoop and Holler Bend) near the city of Portage La Prairie in order to allow water to flow overland, sparing the more densely populated areas closer to the city of Winnipeg. This plan, while designed to protect 850 homes and 500 square kilometers of farmland, may flood 150 homes and 225 square kilometers that would otherwise not have been so severely affected.  Flood management has always been about moving the risk around. Early in the 20th century, federal government district engineer J. E. St. Laurent worried that flood-fighting at particular locations along the Assiniboine would inevitably worsen the situation for other places. St. Laurent felt that flood protection efforts underway in 1922 would simply “throw the whole volume of flood water further down the river,” threatening areas that may otherwise have been spared.  The situation at Hoop and Holler Bend is an especially dramatic and high-stakes example of the calculus that has always been part of flood fighting. 
This flood is big. No question about that. Land has been inundated and lives have been devastated. But from an environmental history perspective, calling it “without precedent” does not seem quite correct, given the existing historic and prehistoric evidence about flooding and flood-fighting along the Assiniboine River and across the province of Manitoba.
So how, then, can we understand the use of the phrase “without precedent,” whether by provincial spokespersons or by media commentators? Is this simply the sort of intellectual shortcut sometimes taken by those under pressure to get the word out? Perhaps. However, I think this phrase might also signify something more interesting. I think it marks the difficulty of remembering environmental events, and the challenge of incorporating into our actions what we do retain from moments of crisis. Places of historic or environmental significance can be safeguarded relatively easily; it is more difficult to preserve the memory of events that come and go, even when the events in question are as dramatic as Manitoba’s floods. The phrase “without precedent,” then, tells us more about the limit of collective memory than about the height of the water.
(Thanks to Sean Kheraj for encouraging me to write about all of this, and to Jim Clifford for being receptive to my contribution.)
 A clear description of the concept of recurrence interval can be found here: http://ga.water.usgs.gov/edu/100yearflood.html
 W.F. Rannie, “Assessment of the historic hydrology of the Assiniboine River and watershed, 1793-1870” Geological Survey of Canada Open-File 4087, Ottawa, 2001.
 Scott St. George and Erik Nielsen, “Flood Ring Evidence and its Application to Paleoflood Hydrology of the Red River and Assiniboine River in Manitoba” Géographie physique et Quaternaire, vol. 56, no. 2-3 (2002): 181-190.
 Shannon Stunden Bower, “Natural and unnatural complexities: flood control along Manitoba’s Assiniboine River,” Journal of Historical Geography vol. 36, no. 1 (January 2010): 57-67.
 Library and Archives of Canada, RG 11, Vol. 4354, file: 5816-1-B, District Engineer J.E. St. Laurent to Chief Engineer A. St. Laurent, 29 July 1922.
 See my 24 April 2011 Nature’s Chroniclers post that addresses this issue in relation to the operation of the Red River Floodway. http://niche-canada.org/node/9960