Water Resources of the United States

PROJECT ALERT NOTICE (CO) Post-Flood Field Observation for Colorado Flood

Date: Thu, 26 Sep 2013 00:19:52 EDT

Summary: Post-flood field observations and survey work in Fourmile Creek, Colorado preliminarily indicates a "wall of water" pulsed through Fourmile Creek around 10:45 PM local time on September 12, 2013.

A team jointly staffed by the Office of Surface Water and the Indiana Water Science Center conducted surveys of Fourmile Creek at Orodell, CO and Fourmile Canyon Creek near Sunshine, CO. The surveys are for the purpose of determining the peak discharges at these locations. Both of these streamgages monitor the flow coming from the Fourmile Burn area and are high gradient mountain streams.

Access to these sites has been restricted by Colorado National Guard and Colorado Highway patrol because of severe damage road and housing structures in the area. Numerous landslides were noted along Boulder Canyon Road (the road used to access the site) with significant road damage. Along Fourmile Canyon Road, numerous houses were damaged and large sections of the road have been partially destroyed (see attached photograph).

In the reach of the Orodell streamgage, the channel appears to have downcut by as much as 1 to 2 feet. Residents speak of a "wall of water" coming down Fourmile Creek in the area of the Orodell streamgage. Traditionally, flash floods have a rapid rise and fall that people sometimes mistakenly refer to as a "wall of water". However, a spike in the stream elevation (rapid rise and fall in 5 minutes) on the streamgage at 10:45 PM Mountain time was verified by high water marks collected by the survey team. The rapid rise and fall appears to be around 4 feet in less than 5 minutes. This same spike was not evident on the upstream streamgage at Logan Mills Road. Based on field evidence of deposition and severe destruction upstream, the survey team speculates that a debris jam upstream (between Logan Mills Road and the Oradell streamgage) formed and breached sending a true "wall of water" sloshing downstream. This sloshing is evident in the difference in high water mark elevations of as much as 1 foot alternating from one side of the river to the other side.

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