The September Flood: Five Days in 2013

Boulder sits at the mouth of a canyon. The city has always known this about itself, but the knowledge became vivid in September of twenty thirteen.

Between the eleventh and fifteenth of that month, a weather system stalled over the Front Range and delivered extraordinary rainfall. On September twelfth alone, nine inches fell on Boulder County in a single twenty-four-hour period, nearly double the previous record. The county's average annual precipitation is about twenty inches. In five days, they received roughly eighteen.

Boulder Creek, which runs through the center of the city, rose fast and carved new channels. Creeks in the foothills came down with logs and boulders and the debris of steep terrain. The town of Lyons, twelve miles north, was isolated when St. Vrain Creek flooded both access roads. More than eleven thousand people were evacuated across the region. Nearly nineteen thousand homes were damaged; more than fifteen hundred were destroyed.

Eight people died across the affected counties. Dozens of state highway bridges were damaged or swept away. Total damage across Colorado reached well over a billion dollars.

Boulder Creek's banks and path were rebuilt in the years that followed. The open space corridors along the creek, long protected by the city's land policies, gave the water somewhere to spread. Urban planners and hydrologists have since cited the Boulder Creek greenway as a case study in how open space reduces flood damage, a retrospective argument for the decisions made in nineteen sixty-seven.

The canyon walls to the west look unchanged. The creek below you runs clear most days. The history of what happened here is written in the new rock work along the banks.