Freezing and Flooding on Flat Creek

By Phoebe Coburn

On a subzero day in December, I joined Teton Conservation District staff members Carlin Girard, Elyce Gosselin, and Tom Segerstrom to check out some winter flooding just upstream of Smith’s on Flat Creek.

The creek overruns its banks during the coldest months of the year when ice dams block the flow. Frigid temperatures cause two kinds of problematic ice to form in Flat Creek: frazil ice and anchor ice. Frazil ice is created when turbulent water is supercooled (below 32⁰ F) and forms loose or disjointed ice chunks often seen floating down rivers and creeks on cold days. This type of jumbled ice stew is notorious for causing ice dams and flooding. Frazil ice can also solidify along creek bottoms—creating what’s called anchor ice—which causes flooding by displacing creek water upwards.

To help address winter flooding, the Flat Creek Water Improvement District (FCWID) formed in 2014. FCWID is a special district governed by a five-member Board of Directors who are under the supervision of the Teton Conservation District Board of Supervisors. The mission of FCWID is to explore and implement ways to prevent damage to private property due to winter flooding of Flat Creek with a commitment to honor water rights, represent the best interests of the district’s property owners and residents, while maintaining and improving water and habitat quality within the stream corridor.

Winter flooding is a naturally occurring phenomenon and has been recorded on the creek for decades. Flooding serves an ecological role, so the FCWID aims to protect private property from damage more so than they work to prevent flooding. With their members who own property along the creek, FCWID pursues best practices for preventing property damage according to their Emergency Wintertime and Spring Runoff Action Plan. During extreme winter flooding events, FCWID mitigates ice buildup by manually removing ice from the creek using machinery and by advising on the use of thaw wells that pump relatively warm ground water into the creek. They use machinery as a last resort as it presents consequences for the creek’s ecosystem and is a significant financial cost to FCWID members. Property owners along the creek also pursue more proactive measures such as sand bags, berms, and elevated landscaping. FCWID is actively researching ice formation and alternative mitigation tools, hoping to minimize disturbance to the creek.  

Though this winter may seem relatively mild for the old-timers in town, it’s the worst winter for flooding on Flat Creek that FCWID Chair Bill Wotkyns can remember. It’s hard to say why this is, but FCWID and Teton Conservation District hope to gain a better understanding of when, where, and under what circumstances ice forms in the creek through an ongoing study with Alder Environmental, the University of Wyoming, and Colorado State University. To see the findings of this study released in August of 2018, click here.

On the particularly chilly day I went to check out winter flooding on Flat Creek for myself, I was dressed like any local Jackson kid would be: woefully underdressed. After a mere minute or two of walking along the creek near Smith’s, I managed to fall through some crusty looking frazil ice up to my knees. Oops.  When the temperature is well below zero, falling into water will trigger anyone’s fight or flight instinct. Mine was flight. I post-holed my way out of creek and within seconds of reaching solid land, my not-so-trusty clogs instantly fused to my feet. I waited in the car for the rest of the field trip. Carlin was quick to point out the moral of the story: don’t bring clogs to a flood fight.