For hundreds of years, thousands of people have connected with the Mississippi River. Today, we sometimes forget that the Mississippi is always flowing through our fair cities, at least until it floods.
In this moment, the river can be an extraordinarily humanizing resource. When we stand together on the Science Museum's plaza, peek over the rails on Kellogg Blvd.'s parkland, or sit near the steps on Harriet Island, all gazing at the flooding river, we are not accountants, scientists, or novelists but everyday people witnessing an event that still produces the same awe, fear, romance, or dread that thousands of people for hundreds of years before us have experienced when they too watched or experienced a flood.
In future posts, my colleagues and I will chat about the impact of flooding on the Mississippi's landscape and try providing some historical perspectives on river floods.
If you'd like to learn more about our National Park Service unit, the Mississippi National River and Recreation Area, please visit us at www.nps.gov/miss.
-Ranger Brian
Tags : NOAA/USGS and US Army Corps of Engineers (COE) forecast charts are showing a new predicted crest for the Mississippi River here in downtown St. Paul at a whopping 19.8' late on 3/25.
That's 2 feet higher than predicted yesterday, and would make the 2010 flood #7 on the top-ten list of recorded floods at this site.
Watching the river, 3/18/10
in Earth and Space Science, Physical Science, The Water Cycle, Weather and Climate, and Forces of Nature
If you're visiting the Science Museum of Minnesota, look out the windows from the Mississippi River Gallery on level 5. If you're in downtown St. Paul, stop by the museum and look at the river from the overlook on Kellogg Plaza. (City officials are asking folks not to flock to areas where barriers are going up - especially Harriet Island - but the view from in or around the museum is spectacular and safe.)
Kate's photos, 3/18 (3): Looks peaceful, doesn't it? Still, the city is warning people to stay off of the river, out of the low-lying parks, and away from Harriet Island and Water Street.
Courtesy Kate Hintz
The Mississippi is going up FAST today, and forecasters expect that the river will officially reach "flood stage" by early this afternoon. (It's 10:45am, and the river's at 11.67'. It's risen a foot and a half in the last 24 hours, should reach 12' ("action stage") pretty soon, and 14' ("flood stage") by late today.
Kate's photos, 3/18 (2): Look across the river to the floodwall: that's the high-water mark for the 1965 flood, the highest in recorded history. That year, the river crested here in downtown St. Paul at 26.01' and marked the end for the communities then down on the river flats.
Courtesy Kate Hintz
Kate's photos, 3/18 (1): Shepard/Warner roads will close from Chestnut Street to US 61 starting Saturday morning, and could remain closed for weeks. Take your river sightseeing drive/bike ride/walk before then!
Courtesy Kate Hintz
So what's going on around the river?
- The city has closed all city boat launches and temporarily banned all recreational boating within the city limits.
- Water Street will be entirely closed, starting this afternoon.
- Hidden Falls and Lilydale regional parks are closed.
- Flood barriers are going up at the St. Paul downtown airport and at Harriet Island.
- Harriet Island will close once the river reaches 17'.
- Warner/Shepard Roads will be closed from Chestnut Street to US 61 starting Saturday morning in preparation for the construction of a temporary levee that could withstand river levels to 26'. These roads could be closed for weeks, depending on the extent of the flooding.
Here's the latest hydrology graph:
3/18 hydrology graph, 10:15am
Courtesy USGS
High and fast
in Earth and Space Science, Math, The Water Cycle, Weather and Climate, and Forces of Nature
Look out the window or walk down the street to nearly any river or stream in Minnesota right now and you are likely to observe two things about the river:
- it is getting deeper (or “rising” in relation to the banks); and
- it appears to be moving faster.
You can, of course, confirm these observations by investigating reports from gauging stations along these rivers, maintained by the U.S. Geological Survey. (See data for the gauging station serving downtown St. Paul.) But what is really happening?
It may be high and fast...: ...but (as of today) the Mississippi at St. Paul is still in a bankfull state.
Courtesy Liza Pryor
Until a river flows over its banks, it is considered to be in a “bankfull” state. In this state, the water flowing through the river is confined to a relatively fixed channel area. Simply put, floods occur because more water is being introduced into this channel from upstream, due to snowmelt, heavy rains, or a dam breach. As this added volume of water moves through a fixed area, it both increases in velocity and in depth until it overflows the banks, at which point some, but not necessarily a lot, of the volume and velocity moving through the channel are reduced.
Scientists call the rate of flow through a channel “discharge." Discharge is defined as the volume of water passing through a given cross-section of the river channel within a specified period of time.A simple equation for determining discharge is
Q = D x W x V
where Q = discharge, D = channel depth, W = channel width and V = velocity.
Looking at this equation, it is easy to see that if discharge becomes greater and channel width is fixed, then an increase in both volume and depth (or height relative to the banks) is likely to be the cause. Discharge can be measured in cubic feet per second or cubic meters per second, for example.
But is the river flowing at the same rate at the surface as it does along its banks and beds? Understanding this requires investigating some more detailed equations, as the banks and bed introduce friction, which affects the rate of flow.
To learn more about rivers and how they flow, you may want to check out the works of Luna Leopold, and M. Gordon Wolman. In particular:
- Leopold, Luna B. (2006, reprint). A View of the River. Harvard University Press; and
- Leopold, Luna B.; Wolman, M. Gordon; and Miller, John P. (1995). Fluvial Processes in Geomorphology. Dover Publications, both classics for understanding how rivers work.
Also, check out our full feature on the 2010 Mississippi River flooding.
As of 11:19am, the US Geological Survey is forecasting that the Mississippi River will crest here in downtown St. Paul at 18 feet.
New flood crest prediction, 3/17
Courtesy USGS
That would put Water Street and the lower section of Lilydale Regional Park underwater (at 14'), require secondary flood walls at the St. Paul Downtown Airport (17'), submerge much of Harriet Island (17.5'), and make Warner Road impassable due to high water.
An 18-foot crest would also make this year's flood #9, historically speaking, bumping the flood of 1986 (16.10') off the top-10 list.
Also, check out our full feature on the 2010 Mississippi River flooding.
Minnesota Public Radio featured the new Saint Paul condo developments, down by the Mississippi River, this morning. The Mississippi is predicted to reach flood stage by Friday, and these folks are going to have a pretty good view of the rising water. Check out our full feature on the rising Mississip', with a time-lapse of the river's rise.
Watching the river, 3/16/10
in Earth and Space Science, Physical Science, The Water Cycle, Weather and Climate, and Forces of Nature
All day, up in the Mississippi River Gallery, people have been stopping to look out the window and watch the river.
Here's how the US Geological Survey sees it:
Mississippi River, actual vs. forecast, 3/16/10, 1pm
Courtesy USGS
The river's rising, but not as fast as yesterday. And yesterday's rise outpaced predictions by almost a foot, but today the rise matches the predicted curve almost exactly.
So what are folks seeing out the window? Take a look.
Also check out our full feature on the 2010 Mississippi River flooding.
Watch the steps: They're a good benchmark.
Courtesy Liza Pryor
Raspberry Island: Still high and dry
Courtesy Liza Pryor
Looking upstream: You're still looking at Harriet Island. But low-lying areas of Lilydale (upstream, south side of the river) get inundated when the river reaches 14 feet or so. Right now, that's predicted to happen sometime after 7pm on Sunday, 3/21.
Courtesy Liza Pryor
It's been a very snowy winter so it should come as no surprise that the flood risks in Minnesota are going to be high as well. There's a 60-percent chance that the Mississippi River will be creeping up close to our backdoor here at the museum in the latest forecast announced today. Start packing the sandbags right now in Moorhead and Fargo. There's a 98-percent chance that the Red River will flood this spring.
Underwater, or “internal” waves, unlike the familiar wind-generated surface waves, occur due to density stratification often generated by coastal tides. These internal wave can lead to redistribution of nutrients and minerals. Internal waves can also cause vertical “velocity shear”, intensifying the vertical mixing process within the water column and bringing suspended particles and nutrients to the surface. Understanding and tracking these internal waves is another way to monitor the vital signs of an estuary.
Internal waves
Courtesy CMOP
CMOP successfully launched its new autonomous underwater vehicles (AUV) to help scientists gain a better understanding of the Columbia River estuary. One of the first studies to use these vehicles will be directed at internal waves. Craig McNeil, oceanographer from the Applied Physics Laboratory at the University of Washington and CMOP investigator, is using AUV’s to study the generation and propagation of internal waves in the Columbia River estuary and plume. He's interested in the physics of internal waves and mixing near the sea surface and the sea floor.
McNeil said,
“Scientists speculate that some bottom following internal waves have closed circulations that traps water and biology. The AUVs will help us sample these waves so we can better understand these complex mixing mechanisms.”
One upcoming experiment will study the dynamics of the freshwater plume as it spreads out over the denser saltwater of the coastal ocean. Of particular interest is to compare measured observations with theoretical predictions. McNeil will program the vehicles to travel into the advancing plume and navigate through the plume front. This will allow CMOP to study the progression of internal waves that are known to be generated at the advancing plume front and determine their propagation speed.
Watch researchers deploy the AUV: Watch Craig, Troy, and Trina deploy the AUV in the Columbia River.
Courtesy CMOP
Before those measurements could take place, McNeil needed to test the vehicles’ capabilities in the field. Along with oceanographer Trina Litchendorf and field engineer Troy Swanson, McNeil tested the vehicle in Lake Washington over the winter months. By spring the team was ready to take it through its paces in the Columbia River estuary.
They traveled to Astoria, Oregon, and met up with CMOP’s field team for the vehicle’s first mission in the river. They decided initial tests would be conducted during slack tide due to the limits of the vehicle in strong currents. The mission was based on tidal cycle information supplied by CMOP’s cyber-team. The expected velocities during slack tide would be less than 0.5 m/s or about 1 knot, which was in the acceptable range for the vehicles
The vehicle was deployed near the first transponder set by the team in the North Channel of the Columbia River. There it performed a compass calibration and proceeded to its first designated waypoint. To make sure it was on track, McNeil monitored the vehicle’s position with a device called the Ranger. The Ranger's transponder receives status updates from the vehicle.
Water temperature map: This figure shows a map of water temperature recorded by the CTD on the AUV during its first mission in the North Channel of the Columbia River estuary westward of the Astoria Bridge.
Courtesy CMOP
The results of the mission were a success. The vehicle traveled upon its designated coordinates and collected salinity and temperature data. Now the team has a better understanding of how to control the vehicle’s navigation in the river, which means it will be able to perform longer missions.
McNeil and his team will now use the AUVs to study various physical processes in the Columbia River estuary, including internal waves, currents, and mixing of various biogeochemical components of the water; all of these adding to our understanding of the estuary’s vital signs.
More photos of the AUV deployment: More photos of the AUV deployment
Courtesy CMOP
Estuaries are coastal areas in which rivers and oceans meet. Thus, they include both fresh and salt water, each of which support different ecological communities of plants and animals, large and small. Salinity (“saltiness”) of the estuary is a measure of its health--a vital sign--for those communities.
In some cases, salt-water from the ocean side of the estuary can begin to “intrude” on an area previously dominated by fresh water. It is important to be able to measure and monitor this aspect estuary health.
CMOP has developed a remote sensing device that opens the way for scientists to better understand and predict salinity intrusions in estuaries.
Circuit analog for dipole source on river bed
Courtesy CMOP
Oceanographer Thomas Sanford, Ph.D., and his team from the Applied Physics Laboratory at the University of Washington, have developed a bottom-mounted instrument for measuring electrical conductivity in the water column, which can be transformed into salinity readings.
The current process for measuring salinity involves sensors that provide “point” observations. Sanford’s instrument provides measurements of integrated salinities across the entire water column, allowing a more representative description of salinity intrusion.
How does it work?
Sanford’s approach is to produce a low-frequency electrical current and measure the resulting electric field at a nearby dipole receiver. The received electrical field is a function of the electrical conductivity of the water column and the sediments.
Quasi-static electrical analog circuit: The quasi-static electrical analog circuit for electric currents divided between the parallel resistors of saline water (Rw ) and the sediment (Rs ) is such that: Vr /Is = CRwRs /(Rw + Rs ) = C(Σw + Σs )-1 , ∴ Σw = CIs/Vr – Σs, where Σw is the conductance (vertical integral of σ) of the river, C is an empirical calibration value, Is is the source current, Vr is the receiver voltage and Σs is the conductance of the sediments
Courtesy CMOP
Sanford’s team deployed the system in the Columbia River estuary before and during a flood tide. At the same time, they took measurements with a CTD, a standard oceanography-sampling device that reads Conductivity, Temperature and Depth. As the layer of seawater thickened, they observed the decreased resistance of the water column caused the receiver voltage to decrease.
Previous studies in the Columbia River had demonstrated a tight correlation between electrical conductivity and salinity. This correlation permits the conversion of electrical conductivity to salinity. Sanford’s team collected a time series of water-column electrical conductivity that they converted to salinity. The inferred salinity was shown to agree with the salinity readings from the CTD.
Vertically integrated salinity: Observed vertically integrated salinity from CTD casts (red dots) compared to that inferred from the electrical measurements using the electrical conductance time series fitted to the equation: Sw = 8.82*(CIs/Vr -Σs ), where C is an empirical coefficient equal to 43, Is is source current and Vr is observed electric field and Σs an offset caused by leakage into the sediments equal to 8. Blue dots are observed electrical conductance and the continuous curve is the electrical conductance, both converted by salinity by the factor 8.82 psu/S/m.
Courtesy CMOP
What's next?
CMOP researchers are looking at Sanford’s new sensor as an opportunity to better explain processes as diverse as internal waves, estuarine turbidity, and summer blooms of phytoplankton (tiny mobile plants that sometimes collect in massive “blooms” in surface waters in estuaries). They expect to improve computer models that are designed to depict the variable conditions of the estuary, and anticipate changes associated with climate and human impact. Once demonstrated for the Columbia River, the new sensor has the potential to be used in estuaries around the world.
Subscribe
I want to learn about
Science Buzz is supported by the National Science Foundation.Copyright © Science Museum of Minnesota, 2004-2010, except where noted.
Add a new comment