KOLD Investigates: Ground soaked, flooded before train derailment NW of Tucson

New report on Marana train derailment

TUCSON, AZ (Tucson News Now) - While federal teams and Union Pacific investigate the train derailment northwest of Tucson earlier this month, Pima County has compiled a report on storms that hit the area with a powerful one-two punch in 48 hours.

Long before the derailment, monsoon flooding rushed through the streets of some neighborhoods in Marana and the northwest side on July 8. The county report considered the storm to be 'low intensity' but it saturated the ground with 2 to 3.5 inches of rain over a few hours.

The storm on July 10 hit the same area with 'high intensity' for 30 minutes to an hour, according to the report. The rain gauge at nearby Arthur Pack Regional Park collected more than an inch of rain in the first ten minutes of the storm.

It was the perfect storm, according to Pima County Regional Flood Control District Deputy Director Andy Dinauer. He said the already saturated ground combined with the powerful second storm created what was likely a 100-year flood event.

Dinauer watched video from the Union Pacific train involved in the derailment. He said it appeared that limbs, mud and other debris stacked 4-5 feet high covered the tracks. The county report estimates the debris stretched for close to 50 feet long.

Pictures in the official report illustrate how the county's retention basins collected water without any overflow. Nearby washes, including some that rarely experience any water flow, carried water in the July 10 storm. Dinauer credited preventative maintenance and the overall infrastructure for doing its job in this situation.

Union Pacific is investigating the derailment, so is the Federal Railroad Administration. There are two tracks in the area. The water rushed over one the eastern tracks and under the western set, according to the county report. The derailment occurred on the western tracks.

"The floodwaters and debris overtopped the railroad due to the blockage on I-10 and the railroad culverts from sediment and debris," according to the county report.

Dinauer said that Pima County compiled the report for informational purposes.

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