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The tricky timeline of a flash flood shown in five charts

Posted at 6:04 PM, Jun 30, 2021
and last updated 2021-06-30 20:04:58-04

SALT LAKE CITY — U.S. Geological Survey Streamflow monitors give us data on Utah’s waterways and precipitation in 15 minute increments, allowing us to see the timeline of a flash flood that swept through Zion National Park and Springdale on June 29.

The rain fell on Springdale at 2:30pm.

The wall of water hit the North Fork of the Virgin near Springdale at 5pm.

It was another four hours before the Virgin swelled at the spot where it enters Quail Creek Reservoir.

The river remained a stream through St. George through the same time period, thanks to the management of reservoirs upstream.

Those reservoir managers released excess water starting just before 7am June 30, and St. George saw a strong and steady flow.