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July 7, 2007

Watching, tracking river conditions

Geological survey keeps daily river log

John Cross

If you drive across the Veterans Memorial Bridge with any regularity, perhaps you’ve wondered what the fellow leaning out over the edge with the pulley-and-wheels contraption every so often is up to.

It’s all part of an on-going survey by the United States Geological Survey of water conditions on the Minnesota River.

The USGS is the federal agency charged with mapping the country, assessing its geological resources and hazards, understanding its natural biological resources, and providing hydrologic information for water resources.

According to its mission statement, information the USGS gathers is used “to contribute to the wise management of the Nation’s natural resources and to promote the health, safety and well being of the people.”

The monitoring station on the Veterans bridge is one of six stations stretching from the Minnesota River headwaters at Ortonville all the way down to Ft. Snelling where it finally dumps into the Mississippi River.

On a daily basis, a volunteer from Minnesota State University unlocks the large box located on the upstream side of the bridge and cranks down a bronze weight shaped like a fish into the current to gather water samples to measure sediment levels.

But every six weeks, Dan Daly, a hydrological technician, travels from the USGS’s Moundsview Office to Mankato to spend four hours doing a complete assessment of river conditions.

Daly charts current speeds and suspended sediment particles from a half-dozen different areas of the river bed by lowering a floating device called an acoustical Doppler system that sends signals back to the rugged laptop computer he wears over his shoulder, down to the water.

In addition, Daly uses a portable crane to lower another fish-shaped weight down to the water at each of those points to gather more water samples to determine sediment load rates. Finally, he gathers material from the river bed that will be used in an on-going Minnesota Pollution Control Agency study on phosphorus levels.

The samples and data Daly gathers year-round provide a real-time picture of such river conditions as flow rates and sediment loads.

Over the long-term, the data collected by the USGS can be used by other agencies to determine trends in water quality and for predicting flood and drought conditions.

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