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usgs now gaging the complete lower minn 

Till now, the US Geological Survey (USGS) and other interested parties have not had accurate readings of Minnesota River discharge into the Mississippi at Ft. Snelling because they would have been too complex and expensive. 

Complex and expensive

The complexity owes to the hydraulic effects of water flowing back into the Minnesota from the Mississippi, including:

• The variable backflow of the Mississippi itself 

• The turbulence contributed by Lock and Dam 2

• The waves generated by barge traffic 

• Other water discharged into the river between Jordan, 40 miles upstream, and the mouth

The expenses to accomplish accurate readings would run about $80,000. This year, finally, such funds became available when the USGS contributed $41,450 of its own funds and was matched by a grant from the District. With these monies, the USGS purchased and installed in January a new Acoustic Doppler Velocity Meter (ADVM). Thanks to this instrument, the USGS is much closer to knowing just how much water is flowing into the Mississippi at Ft. Snelling — and thus to estimate the pollutant loads contributed by the Minnesota River.

Up to this point, the USGS has estimated discharge at the mouth by adding 5 percent to the Jordan gaging-station flow based on “a dye-dilution study,” says USGS Hydrologic Technician Eric Wakeman, “we’d done 30 or so years ago.”

The ADVM is just part of the equipment that the District and the USGS have jointly purchased. It’s a $7,000–8,000 device, “a little smaller than a trashcan,” says Wakeman, “with two horizontal beams that shoot out into the river and one beam at the top to measure river stage.” Over time, as the USGS develops a model of flow at the river mouth through both high and low stages, it will know pretty accurately just how much volume is being discharged. And, by inference, how much contamination as by nutrients and sediment.

Near real-time data posting

The ADVM and a special thermometer (called a “thermistor”) are submersed below a pier and catwalk upstream of Fort Snelling constructed by Metropolitan Council Environmental Services (MCES). Readings are sent via a cable to a gage house mounted on an FAA tower, from where they’re transmitted via satellite to the USGS’s Mounds View office and published to the web. The USGS mounted the gage house on the FAA tower so that it’s higher than the water levels of historic floods. (Water quality is measured at this site, too, and samples are analyzed in the MCES labs in St. Paul.)

For a good look at these nearly–real-time data — water height, velocity, temperature and precipitation — go to the USGS web site. 

The lower Minnesota model

The water-flow data are important, finally, because they will be part of the MCES’s new $1 million Lower Minnesota River Model. Without knowing just what enters the Mississippi at Ft. Snelling, it’s hard to know how we can slow down or stop impairments to the water quality of the Mississippi.