Five years ago flood waters caused immense damage along Colorado鈥檚 northern Front Range and foothills, killing nine people, upending the lives of thousands of others. And just as the raging water left a lasting imprint in the minds of those who lived through it, it did the same to the land itself.
During four days of rain, and weeks of receding, rivers altered course, reservoirs filled with sediment, and soil slipped down hillslopes, ending up as sand bars and log jams downstream. The change was so abrupt and sudden maps had to be redrawn.
After the flood, Sara Rathburn, a fluvial geomorphology professor at Colorado State University, recalls feeling disoriented along the Big Thompson River in its canyon downstream of Rocky Mountain National Park.
鈥淚 couldn鈥檛 locate myself in some places along that channel,鈥� Rathburn says. 鈥淎nd I thought, 鈥榃ow, this is so fundamentally different.鈥欌��
Fluvial geomorphology is, put simply, the study of what happens when water and land meet. Rathburn grew up in Boulder and has spent countless hours hiking Front Range foothills and canyons and holds an intimate knowledge of how these rivers look and function.
As the anniversary of the 2013 floods approached, I asked Rathburn, an expert in how floods change landscapes, to take me to a few places along the Front Range that illustrate just how differently things look now than they did before the flood.
She said to really see the lasting effects of the storm, we should visit North St. Vrain Creek upstream of Ralph Price Reservoir, the city of Longmont鈥檚 main drinking water supply.
The reservoir is held in place by Button Rock Dam. The floods put it to the test 鈥� not just by the massive influx of water, but the trees, boulders and sediment carried downstream. Sand bars made of chunks of cobblestone the size of sourdough loaves were left the reservoir鈥檚 delta, where the creek empties into the lake.
Rathburn and her students, including graduate researcher Johanna Eidmann, have worked to figure out the floods鈥� impact on the reservoir. According to their estimates, the amount of sediment deposited in the lake during those four days of rain in September would normally take 100 years to build up.
From above you can see the changes. An area that was once a backwater for the reservoir completely filled with sediment carried downstream, a product of the nearly 100 landslides the creek鈥檚 watershed saw between the reservoir and Route 7 near Allenspark.
Along the creek, the flood waters became charged with sediment. As the water churned, the sand and rock-laden mixture scoured the creek bed and widened it. Like taking a piece of sandpaper to a cutting board, vast reaches of St. Vrain Creek were reduced down to bedrock, all soil and vegetation swept downstream.
It鈥檚 easy to think of floods purely as destructive, especially as people have built more structures in floodplains. But Rathburn cautions against that thinking.
鈥淔loods are beneficial to river ecosystems鈥� Rathburn says. 鈥淎nd if we can think about rivers as ecosystems, especially places like [Ralph Price Reservoir] that are preserves, but getting that thinking down into communities, beyond open spaces and preserves, I think will set us up well for the future and for these big floods that are hard to comprehend, but they occur.鈥�
We stopped by the reservoir鈥檚 ranger station to meet with Jamie Freel. He鈥檚 the city of Longmont鈥檚 watershed ranger and manages the preserve that surrounds the reservoir. For most of the year he lives alone there, surrounded by rocky slopes and evergreen forests. In September 2013 he was on duty.
鈥淭he day of the flood I just remember the sheer scale of the thing,鈥� he says. 鈥淚t was moving faster than we could really comprehend what was happening to us.鈥�
Freel watched as the reservoir he鈥檚 tasked with overseeing turned the color of a 鈥渕ocha latte.鈥� It was filling so quickly the spillway was needed to lessen the pressure on the dam.
Before the flood the spillway channel looked like 鈥渁 Coors ad,鈥� a gentle cascade of lichen-covered rocks, trees and shrubs.
As the rain continued the spillway raged so violently helicopter pilots flying out residents in the foothills could see it from miles away. Whitewater rose so high rescuers nicknamed it 鈥渢he angry dam,鈥� and used it as a landmark to coordinate rescues.
鈥淚t was like a freight train,鈥� Freel says. 鈥淎ctually, it was more than one freight train. It was several freight trains. It was quite a sight to behold and to hear too.鈥�
I ask Freel if -- five years later -- he still thinks about the flood. Not in a deep way, he says, but he has to think about it in some way every day because he鈥檚 still working on recovery and restoration projects. Until the anniversary comes each year.
鈥淢y body (remembers) every year. I go through -- I wouldn鈥檛 say it was PTSD -- but there is a definite cell memory to the beginning of September. I feel awkward at the beginning of September,鈥� he says.
Downstream, near the city of Longmont, Rathburn and I chat with Ken Huson, the city鈥檚 water resources manager. We stop on a pedestrian bridge over St. Vrain Creek in the Sandstone Ranch nature preserve. It鈥檚 a wide, shallow stretch of the creek. While we talk a dozen or so bicyclists ride past.
Before the flood, the river didn鈥檛 flow here. It was a couple hundred yards away. But the flood forced it to change course.
鈥淩ight here during the flood you basically had a half mile wide of chocolate brown water,鈥� Huson says.
During the flood, Huson took a helicopter up to Ralph Price Reservoir to make sure the dam was holding. From the air he saw rivers and streams jump their banks, carving new channels and abandoning their old ones.
鈥淭he toughest part was flying almost to Lyons and I saw someone鈥檚 house floating down the creek, and starting to turn and tear and -- knowing it was someone鈥檚 house -- watching it being destroyed right underneath you was really hard,鈥� Huson says.
He says systems can be rebuilt and the landscape can change, but its the human impacts of the flood that remain the hardest to comprehend.
