500 Bridges. 5 Days.

SEH bridge inspectors paired off in five teams of two and assessed the safety of bridges across three Colorado counties. To complete the process promptly, the teams conducted nearly 100 inspections per day. Unfortunately, the very conditions that damaged the bridges at times made it difficult to reach them.

After devastating floods overwhelmed parts of northern Colorado, the Colorado Department of Transportation (CDOT) called on SEH bridge inspectors to assess the safety of hundreds of bridges throughout some of Colorado’s most flood-afflicted regions.

Unprecedented floods surged throughout northern Colorado last September, washing out roads, moving homes from their foundations and uprooting thousands of residents. In the aftermath, 10 SEH bridge inspectors had a critical task ahead of them: assessing hundreds of potentially compromised bridges throughout Colorado’s Front Range. They would need to investigate nearly 100 bridges per day in order to complete the task. Not a moment was wasted.

map graphic
The colored dots represent the bridge locations across Boulder, Larimer and Weld counties in north central Colorado. The five colors (green, orange, purple, blue and grey) represent the five teams of two inspectors who were charged with the triage inspection of an average of 100 bridges per day over a five-day period. To help speed up the process, the teams used a specialized Google Docs template to upload their inspection reports and provide CDOT with real-time updates.

Strategy

Pairing off in five teams of two, the inspectors distributed the inspections – which encompassed three of Colorado’s most populated counties: Boulder, Larimer and Weld. Using an abbreviated inspection process provided by CDOT, the teams worked 12-hour days and performed nearly 100 inspections per day. Unfortunately, the very conditions that damaged the bridges at times made it difficult to diagnose them.

Many roads were impassable, bridges completely washed out, making it difficult to move quickly. In some cases, we had to circle back to bridges a day or two later, when conditions improved enough for us to assess them.
Jason Triplett, PE, SEH Structural Engineer and blue team inspection leader

To help speed up the process, the teams used a specialized Google Docs template to upload their inspection reports and provide CDOT with real-time updates, which were coordinated by State and National Guard teams.

Bridge scour: the most common inspection

The most common inspection finding that SEH crews encountered was bridge scour. Scour occurs when the bank around the base of the bridge abutments is washed away and the soil is carried downstream by flood waters.

Without the bank to protect the base of the bridge foundation, the flood water and debris erodes the foundation of the bridge. In some cases, heavy scour has caused older bridges to wash away completely.

“Moving forward, new bridges will need stronger, deeper foundations and more effective riprap to reduce and prevent scour,” says SEH Structural Engineer Jason Triplett, PE.

Lesson learned

Though stronger, more flood-resistant bridges can reduce flood damage to bridges, SEH bridge inspection teams gained a better understanding of the level of effort required to respond to future flooding events.

While there is no way to prevent future flood conditions from occurring, the lesson learned is how SEH can respond to natural events that are beyond human control in a way that helps save lives and minimize loss of property.

 

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