It’s often said that we know less about the oceans than we know about the moon, thanks to the priorities that have guided scientific investigation of our home planet.
Sometimes it seems we know still less about the water beneath our feet: how much of it there is, how reliably it’s being replenished, how long our ever-increasing demands on it can be sustained.
Many interesting glimpses into our reservoirs of groundwater knowledge and ignorance were laid out in a talk last Thursday evening, sponsored by The Freshwater Society and the University of Minnesota’s College of Biological Sciences.
The speaker was Don Rosenberry, a Colorado-based hydrologist with the U.S. Geological Survey whose specialty is the interconnection between groundwater and surface water. In the words of his lecture title, rising social concern has made this a topic that’s “Not Just for Scientists Anymore.”
Rosenberry’s recent assignments have included the predicament of White Bear Lake, and he touched repeatedly on that lake’s falling levels to illustrate what we know and don’t know about how water moves back and forth through lakebeds.
(Interestingly, fewer than 10 among the 170 of us in attendance raised a hand when Rosenberry asked how many had come to the event because of a specific interest in White Bear Lake — perhaps a sign that the topic is indeed developing the broader public following it deserves, given that we count on this resource for most of the water we drink.)
His key points about White Bear Lake:
- As you might expect, the lake’s levels have tended to rise with above-normal precipitation and fall with below-normal amounts, typically after a few years’ lag. Since about 2005, however, the linkage has been broken, and the lake levels have been falling sharply and independently of the precipitation curve.
- Monitoring of flows near the lake surface show groundwater moving into the lake in about 18 places and out of the lake at only one, the connection to Bald Eagle Lake.
- However, water at deeper levels of the lake is moving down through the lake bottom and into buried aquifers, replacing water drawn out through wells. Scientists can determine ultimate source of well water based on analysis of oxygen isotopes; some wells near White Bear are delivering 75 percent lake water, and just 25 percent groundwater.
Can White Bear rebound? Maybe
Asked if the White Bear findings can likely be projected to other lakes and wells and in the northeastern metro area, Rosenberry said they thought they probably could be, but more research would be needed to know for sure.
Asked if there was any reasonable expectation that White Bear Lake could rebound without extraordinary measures — like proposals to pump groundwater into the lake — Rosenberry said he thought that was indeed possible, because of surprising patterns of resilience and recovery he has seen in other situations that seemed as dire.
Two cases in point:
- Near Kalamazoo, Mich., lakeshore property owners seized on extraordinary measures when their beloved Long Lake began to retreat to a degree that looked — at least in aerial photos — much worse than White Bear’s current all-time low.
They pooled their funds and sank a well capable of pumping groundwater into the lake at a rate of 2 million to 3 million gallons a day. But the lake refused to respond as expected. USGS examination of the lake bed found that it was doing its job of holding water at the surface — except in one small, porous area that happened to be just offshore from the new pumping station, and was circulating the pumped water right back to the well.
- Between Park Rapids, Minn., and Walker, rising levels in Lake Belle Taine were causing resorts to shut down, inundating septic systems, closing roads with prolonged flooding — and moving county commissioners to consider drastic, expensive solutions.
The options seemed to include digging new outlet channels, pumping the water to irrigation operations or impoundment lagoons, or somehow manipulating an unusually porous lake bed — which was already moving 22 million gallons a day into the Crow Wing chain via underground connections — to drain the lake even faster. But before they could decide on the best course of action, precipitation returned to more normal patterns, and the lake to more normal levels.
Belle Taine’s problems might not be solved for good, though, because the record now shows a steady, upward trend in both precipitation and lake level. This is happening in many other places, Rosenberry said, “as we enter a period of more frequent extremes” in weather.
Unique features of climate and geography in Minnesota mean that very little of our water comes from outside the state, and the balance between precipitation and evaporation remains delicately in balance — for now.
But in other parts of the country, Rosenberry said, there’s no doubt whatsoever that we are now “mining water,” pumping it from the ground at such rates that it can’t be replenished for 1,000 years.
Tools of the hydrology trade
Because I know so little about hydrology, I was fascinated by some of the technical sidelights of Rosenberry’s talk — including the main instrument used for measuring flows of water back and forth through a lakebed.
The “half-barrel seepage meter,” developed in the 1970s by a University of Minnesota student, consists of the cut-off end of one of those blue plastic 55-gallon drums, a bit of tubing and a plastic bag.
The bag can collect water moving up through the lake bottom, or can be filled with water to measure its flow down through the bottom. It looks kind of discarded junk and is, as Rosenberry says,”about as simple and cheap as science gets.”
Unfortunately, using these simple tools is labor intensive, therefore expensive, and thus the pace of research proceeds slowly, often driven by alarming situations on the order of White Bear Lake’s.
For a close-up look at these tools and their uses, as well as a fairly hilarious look at the new “USGS Air Force” created with cast-off drones from the Pentagon, you can check out Rosenberry’s talk here.
Good news on bad intersection
Odds appear to be increasing that the Minnesota Department of Transportation will upgrade an especially dangerous intersection where Goodhue County 9 crosses U.S. 52 south of Cannon Falls.
This long-awaited project was among those listed by Jim Erkel, a transportation expert with the Minnesota Center for Environmental Advocacy, in last Tuesday’s post about his views that the Stillwater bridge project’s cost can be measured not only in millions of dollars but lost lives.
Crashes at the intersection have killed at least five people in the last 10 years, but the $10 million to $20 million needed to upgrade it hasn’t been available.
On Thursday, the Cannon Falls Beacon reported that MnDOT engineers have come up with a simpler solution that will reduce the cost to about $8.5 million.
The story quotes MnDOT Commissioner Charles Zelle as saying his staff has “been turning over the couch cushions” to find money for the project, and that federal money available for low-cost accident-reduction projects may also be available.
Zelle is quoted as saying the project is clearly a priority for the department, and would “score very high in the Corridor Investment Management Strategy grants due to be announced in the coming weeks.”
And on Monday, the Rochester Post-Bulletin reported that the project’s chances had improved because MnDOT’s share of the cost had been reduced:
Goodhue County submitted a revised Corridor Investment Management Strategy application to the Minnesota Department of Transportation on Tuesday seeking significantly less dollars for the construction of an interchange at U.S. 52 and Goodhue County Road 9. The county reduced its funding request from $8 million to $2.1 million, which figures to make the project more palatable to MnDOT decision-makers.
“Since they’re not asking for as much money, I would suspect that they, perhaps, have a better chance,” MnDOT Public Affairs Coordinator Kristin Kammueller.
The paper also reported that the most recent fatality at the intersection — the death of Sharon Gates-Hull of Northfield on May 9 — had made it the most dangerous intersection in Minnesota, according to state officials.