The Lyons Emergency Flood Channel—One Year Later

lyons flood channel
The Lyons Emergency Channel and McConnell Flood Berm at peak design flow.

One year ago S2o Design and Engineering completed an emergency flood channel through the Town of Lyons for the Federal Emergency Management Agency (FEMA).  The channel routed down both the North and South Forks of the St. Vrain and beyond the Confluence for 1/2 mile.  Creation of the Emergency Flood Channel protected the Town of Lyons from subsequent flooding during run-off the following year and allowed the Town time to create and implement a well-designed river restoration project in subsequent years.

It has been almost 16 months since the Town of Lyons, CO was devastated by a 1 in 500 year flood.  Over 30,000 cubic feet per second flowed through a channel that typically peaks at 600 cfs in any given year.  The flood damage rearranged channels, swept away homes, trapped people on any one of seven separate “islands” and left behind a tremendous amount of damage.

The Town itself was evacuated but for those residents who chose to stay and, “essential businesses”.  One of those essential businesses was S2o Design and Engineering.  A local Whitewater Park/River Engineering firm that is based in downtown Lyons.

S2o immediately began to partner with the Town, State, and Federal Government to aid with the recovery.  This included detailed damage assessments, which has helped the Town to recover its losses; immediate damage recovery, such as the design of the work that put the river back under McConnell Bridge and allowed residents to return home, and a number of other, equally important tasks.  We continue to partner with Lyons on the tasks associated with rebuilding this Town.

One of the most important tasks was the design of the Lyons Emergency Channel.  This project was initiated by FEMA, in cooperation with the Town, and allowed for the creation of an emergency channel through the Town.  The purpose of this channel was to create enough flow capacity, in the channel and under the bridges, to accommodate a run-off equal to the 1-in-5 year flood, should that occur in the year after the disaster.   S2o was commissioned to do this work.  A later phase of work is tasked with recreating the natural morphology and restoring the habitats along this reach of the river.  This work is ongoing.

Whitewater Park Design Work
In-Channel construction work as the channel is excavated and armoring is placed to protect homes in the confluence area from further flooding.

The project direction was, get it done right, and get it done quickly.  The Town needed the work completed prior to spring run-off.  S2o commissioned a survey of the streambed throughout Town and, foreseeing the construction, had the surveyor leave stakes and elevations at 400 foot intervals throughout the project area.  S2o Engineer Dan Woolley then used hydraulic software to design and draft a channel that accommodated the necessary flows in both the North and South Channels with S2o designer Christine Clark making the construction drawings in parallel with Dan’s work.

The project also required the design of flood berms to prevent the evulsion of the channel at the failure points that had occurred during the previous flood.  S2o Engineer Nathan Werner, a reformed Dam Engineer, designed berms that protected a number of homes from repeat damage in a project that also allowed the McConnell Causeway to be rebuilt.  The entire project was bid, and built, by March of last year.

It is not often that an engineer gets to their work tested at the extreme limit of design but this project did in fact see design flows this last summer.  S2o Engineer Scott Shipley spent several evenings in May and June with a flashlight inspecting berms throughout the Town.  The result, not a single issue that required maintenance.  Even in a rushed environment each part of the project remains s2o strong one year later!