PROJECT ALERT NOTICE (CO) Survey Team on St Vrain Creek below Longmont, CO

Date: Thu, 26 Sep 2013 21:31:33 EDT

Summary: Severe damage along lower St Vrain Creek noted by USGS survey crews from South Dakota and Colorado.

A survey team from South Dakota and Colorado Water Science Centers have collected high-water mark and channel and bridge geometry data for the computation of peak flood flows on St. Vrain Creek below Longmont, Colorado area. Surveys were completed along the St Vrain Creek at both Colorado Highway 119 and Interstate 25.

During the field effort in this reach, severe damage to private and public property and infrastructure has been observed and documented. At the west Highway 119 bridge in Longmont, flood flows have caused major damage by scouring banks and streambeds and leaving significant deposits of materials in others. the flood overtopped Highway 119 by several feet. Tree and debris piles are common and will take much effort to remove. Overhead and underground electrical and communication lines were damaged by the flooding. A concrete bike path which runs along the river has been destroyed in many places.

At the bridge over St Vrain Creek on I-25 two spur dikes upstream from the bridge were both breached by flood waters. At the state park just upstream of the I-25 bridges, facilities were submerged during the flood by as much as 10 to 15 feet of water. Concrete culverts and sidewalk were washed out and dislodged from their original locations and remain scattered in the creek and floodplain. The constriction of the St Vrain through the I-25 bridge caused large amounts of erosion near the bridges. On the downstream side of the I-25 bridges dikes have been almost completely washed out and the creek has moved to a different course. Many underground utilities are broken and exposed.