Online Lower Minnesota River Watershed District News, June 2004
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 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.
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.)
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.