In 1965, they had slide rules, rain gauges and grave diggers.
Pedro Restrepo, the 65-year-old hydrologist in charge at the North Central River Forecast Center in Chanhassen, can relate to the tools available 50 years ago even as he uses the technology of today. When he first started working in hydrology in the 1970s, the instruments being used were much the same as in 1965.
"I still have my slide rule," Restrepo said, producing from his office the well-worn tool used by engineers and scientists to do calculations before the invention of the calculator.
He compared the vast amounts of data and computer models available to the young hydrologists in his office — all of which can be called up immediately with a few keystrokes on their array of desk-top computers — to the challenges facing their predecessors in 1965. He was asked if he had any thoughts about how the millennials in his profession would react if they had to make flood predictions with only the information and tools available a half-century ago.
"Yeah," Restrepo said. "They will cry."
Comparing Forecasts
On March 19, 1965, the U.S. Weather Bureau reported there was a potential for flooding in Minnesota but "the condition was not considered serious," according to a government report published five years after the floods. As late as March 30, the Weather Bureau predicted that "if snowmelt takes 3 days or more, Minnesota streams will not crest as high as 1952 ...," which meant the Minnesota River at Mankato shouldn't top 24.6 feet.
Restrepo said it would have been standard practice in 1965 to use circumstances leading up to previous floods to attempt to estimate whether the current year's flood would be similar, less severe or more serious.
Along with the 1952 flood, there was severe flooding in 1951 that reached a level of 26.2 feet. But the forecasters had never seen a Minnesota River flood like the one that was headed toward Mankato in 1965 and would ultimately crest at 29 feet.
By April 7, after warm temperatures and heavy rains, the bureau revised its prediction for Mankato — forecasting a crest of 26.5 feet on April 9. A day later, dealing with unprecedented flows of water, the bureau upped its expected crest to 30 feet and said it would occur April 10.
The actual crest in Mankato did come April 10, but at just over 29 feet. So, three days before the crest, the forecast was too low by more than 2.5 feet and a day before the crest, it was too high by nearly a foot.
Mankato's last major spring flood threat in 2011 brought a crest of 25.5 feet on Saturday, March 26. The North Central River Forecast Center's predictions were spot-on when issued Thursday and Friday.
Even with the advances in flood forecasting, Minnesota's unpredictable weather left the hydrologists scrambling a bit earlier that week.
On Monday, March 21, 2011, they predicted a 27-foot crest and upped it to 28 feet Tuesday when rainy weather arrived. Both of those forecasts anticipated a Friday high-water mark. By Wednesday, the crest forecast dropped to 26.5 feet and the crest date was correctly moved to Saturday.
Lots of Data, Variables
A visit to the North Central River Forecast Center, which shares office space with the National Weather Service, demonstrates the impressive technology available — a wide variety of images from satellites orbiting overhead, more data from expansive radar systems, and computers that can crunch years of weather information into models capable of anticipating the future.
But a visit also shows the challenges that remain in predicting what will happen as winter turns to spring in Minnesota.
Service coordination hydrologist Steve Buan runs through some of the variables: the amount of snow on the ground in the drainage basins of all the rivers and tributaries, the amount of moisture in the snow (which can be different than the snow depth), the temperature of the air within the snow (if it's colder, it will slow the snow's melt), the amount of moisture in the ground (dry ground will soak up snowmelt and spring rains), the depth of the frost (water can't soak into frozen earth) ... .
All of that is just about the existing conditions. The flood forecasters also have to consider the impact of future weather because warmer and wetter days can exacerbate the amount of water being inflicted on the landscape.
Even when all of that is calculated, it only deals with the volume of water. The hydrologists also have to figure out where the water will go — and how quickly — to come up with an accurate forecast of how high a river will rise at a particular point on a particular day.
And they're undertaking that challenge across a region that stretches from North Dakota to parts of Indiana.
Buan hasn't been in hydrology quite as long as Restrepo, but he goes back long enough to appreciate the advances in technology.
"When I started, we still used punch cards to communicate with a computer in Washington, D.C.," he said, noting that it reflects not so much his age as how behind the times the National Weather Service was in the late 1980s.
The Olden Days
Buan, though, is intrigued by how his predecessors did their jobs, studying techniques going back to the 1880s.
He pulls out large maps from 1965. They were drawn up in St. Louis, where hydrologists responsible for Minnesota were based 50 years ago. Data were written by hand for various reporting stations at various points around the state, including those sections of land that drain to the Minnesota River. Snow depth was written with a red pen, precipitation on March 16 and 17 was recorded in pencil.
"Everything we take for granted on the computer, they were doing on paper," he said.
A March 23 map includes some ominous numbers written in by the hydrologists: the water contained in the growing piles of snow.
"At Mankato, it was over 6 inches of water content within that snow pack. Up by Montevideo, it was 7 inches. Between New Ulm and Redwood Falls, it's 6 1/2 inches," Buan notes. "So between Mankato and Montevideo, there was a lot of water."
When and how quickly would it be released from its frozen state? The St. Louis-based hydrologists had written on the side of the map the phone number of the Weather Bureau's Minnesota meteorologist — Joe Strub.
How much of that snowmelt would soak into the ground? That depended in part on the depth of the frost, and the hydrologists went to non-scientists from around the state for information on that.
"Mostly the gravedigger reports is what they would have relied on," Buan said.
For precipitation, rain gauges were scattered around the watersheds. Today, radar systems are accurate enough to show precipitation amounts across the landscape — the equivalent of having a rain gauge on every square kilometer of earth.
Could've Been Worse, And Was
In many ways, though, residents of the Minnesota River valley were lucky to have the forecasting they did in 1965. The vast suffering caused by floods earlier in the century, including the Ohio River flood of 1937 that killed hundreds and left as many as a million people homeless, prompted more government investment in weather and flood forecasting.
"People got flooded and they didn't even know it was coming," Buan said.
Mankatoans probably faced that same shock in 1881 when a major flood struck. Buan shows an April 1881 map from the "U.S. Army Signal Services Division of Telegrams and Reports for the Benefit of Commerce and Agriculture." That was what existed for organized weather tracking at the time. The map shows winter precipitation across the United States with darker shades denoting increased amounts of moisture. Upstream from Mankato, the map shows the lightest shade, meaning fewer than 2 inches.
Considering what flowed into rivers that spring, the map had to be dangerously incorrect. The reason is obvious to Buan. No one was recording the amount of rain and snow in that part of Minnesota and transmitting it, by telegraph or mail, to the Army Signal Services.
"What it's telling me is they didn't have any observations," Buan said. "... There probably was significant precipitation, but they just didn't get notification."
©2015 The Free Press (Mankato, Minn.). Distributed by Tribune Content Agency, LLC.
