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Reduction of Streamflow From Upstream Ice Formation

Reduction of Streamflow From Upstream Ice Formation. Brian Connelly North Central River Forecast Center Chanhassen, Minnesota. a.k.a. “Ice Bite”. Ice Bite - What Is It ?. River water temperature is approaching 32°F. An ice cover hasn’t formed on the river yet.

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Reduction of Streamflow From Upstream Ice Formation

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  1. Reduction of Streamflow From Upstream Ice Formation Brian Connelly North Central River Forecast Center Chanhassen, Minnesota a.k.a. “Ice Bite”

  2. Ice Bite - What Is It? • River water temperature is approaching 32°F. • An ice cover hasn’t formed on the river yet. • An extreme cold snap occurs over the course of a few days. • Cold temperatures rapidly generate a stationary ice cover on the river, and freeze some water sources. • Since the river ice is stationary it is removed from the downstream flow, and river levels can drop rapidly.

  3. Ice Bite – Who Cares? • Low water event, not flooding • An ice bite can have temporary but significant impacts on navigation, municipal water supplies, and power plant operations. • River levels typically rebound somewhat after a few days.

  4. Ice Bite Example • St. Louis, Missouri – January, 2003 • Lower than normal precipitation during summer and fall of 2002 • Low water entering winter season • Concern over navigation

  5. Upper Mississippi Air & Water Temperatures

  6. Approximate River Ice Cover Before Event

  7. Approximate River Ice Cover After Event

  8. Air Temperature & St. Louis Stage

  9. Forecasting Ice Bite • Monitor Conditions • Significant portion of river must be ice free • River water temperature must be at or near freezing • Watch air temperature forecasts for prolonged cold snaps • Rule of Thumb • Flow reduced by 50% • Rebounds to about 75% of original flow • Source: Wise forecaster from the NCRFC

  10. Flow Reduction Rule of Thumb

  11. Conclusions • Process isn’t modeled, but it may be possible to predict using an approach similar to some of the ice jam prediction methods. • Potential RFC Forecaster Aids • Plot latest water temperature observations spatially. • Plot latest ice cover/thickness observations spatially. • Plot forecast freezing degree days spatially. • Refine the rule-of-thumb

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