The 500-Year Flood, One Year Later

In the early hours of September 12, 2013, an automated call from the Early Flood Warning System in Loveland, CO, went directly to Kevin Gingery’s cell phone. Gingery is the senior civil engineer for the city and functions as the floodplain manager. This was the first low-level alarm on the Big Thompson River, on the western edge of Loveland. Twenty minutes later, his cell rang again with a second, high-level alert.

Paradoxically, Gingery, along with approximately 250 other Colorado floodplain and stormwater professionals, was in Steamboat Springs, CO, 170 miles away, on top of the mountains, above the storm, attending a forum hosted by the Colorado Association of Stormwater and Floodplain Managers (CASFM). The conference had been scheduled for mid-September because, as all the experts knew, in Colorado “it never floods in September.”

When Gingery received the call it had been raining over the Front Range of the Rockies for three days. By the time it quit, two days later, the storm had stretched 299 miles north to south and a federal emergency had been declared for 15 counties. Ten people lost their lives, and total damages were estimated to exceed $3 billion. The storm was rated by the National Weather Service to be a 1,000-year rainfall event; most drainages up and down the Front Range had experienced at least a 50-year flood, a few were calculated at a 100-year probability, and Lyons, CO–a small town in the foothills northwest of Boulder, located at the convergence of two rivers–experienced what locals termed a 500-year flood. With a $1 million annual city budget, Lyons suffered $50 million in damages.

Naturally, old lessons in floodplain management were learned once again, with several new twists.

Lesson #1: Early Warning Is VitalForecasts Are Imperfect
Weather forecasts issued five days before the storm called for “heavy rain,” but gave no indication this storm would shatter records. Prior to the storm, Dale Rademacher, director of public works and natural areas for the city of Longmont, had been hiking with the city’s new city manager. The National Weather Service had forecast 2 to 4 inches of rain. Flooding along the Front Range usually occurs from thunderstorms in July and August. “Don’t worry. They’re usually wrong,” Rademacher had assured the city manager. “If we get 4 inches here in September, that would be a deluge.” Their city received more than 6 inches of rain in four days.

But Longmont had not received the brunt of the storm. Twenty miles up the road, Boulder received 15 inches in that same short span. Up and down the Front Range, the September 2013 storm exceeded all previous rainfall records for that month. Town after town and city after city were inundated. The previous record for September, set in 1919, was 4.8 inches.

“These are the types of rains one would expect on the coast in a tropical storm,” notes meteorologist Jeff Masters, “not in the interior of North America.” No wonder forecasts are imperfect.

At the National Weather Service, Nezette Rydell reports the organization had received conflicting advice from its various numerical weather models, as well as different outcomes from the same model run at different times. David Gochis, a scientist at the National Center for Atmospheric Research, admits, “We’ve never seen an event like this before, where there were so many critical factors that came together and focused heavy rainfall along the mountain front for such a long period.”

Still, Gingery’s experience with Loveland was a high-end example of what a good early warning system (EWS) can accomplish. The alarms that Gingery and his cohorts received set into motion a well-rehearsed automatic emergency operations plan. Low-lying roads were quickly closed, evacuation alerts issued, and personnel mobilized. At least in Loveland, no lives were lost, and nobody had to be rescued, though many were evacuated.

For Will Birchfield, floodplain manager and building inspector for the small mountain town of Estes Park, an early warning system was more visceral. Seeing how much it was raining, he grabbed his video camera and started walking along the streambanks. The water was roaring. He could hear boulders under the surface of the stream being knocked against each other as they were being rolled down the mountain. “I’ve never heard that before,” he says. “It sounded like thunder that just didn’t stop. I was very careful where I put my feet.”

While Loveland operated with nine gauges, Fort Collins, 15 miles to the north, has an EWS system that consists of 68 gauges, including two US Geological Survey gauges. The city had recently installed extra gauges far up the Cache La Poudre River, which runs along the edge of town, because of concerns about the potential runoff with high levels of debris caused by the previous year’s High Park Fire, which had been a record-setter in its own right. Accurate data from all the gauges rolled in quickly and smoothly, allowing Fort Collins to likewise activate its prepared emergency procedures.

But gauges don’t always tell the whole story. In Boulder, recently retired police chief Mark Beckner comments, “We were finding the [actual] flooding worse than the data indicated. What we were getting in the streets didn’t match what the charts told us should be happening.”

The situation was similar for Longmont’s Rademacher. He had been alerted by a midnight phone call from a park ranger at the city reservoir west of town who laconically told him it was raining pretty hard and the waters were rising. Rademacher’s wife, also a water engineer, began looking at data online, particularly from various sites higher up the canyon. She soon discovered two important stream gauges had been knocked out. “We went blind,” he says. Mobilizing available park rangers and deputies, Rademacher posted observers on bridges crossing the stream, measuring water height with tape measures suspended from bridges.

When reports were in, Rademacher knew something was wrong. The data his wife provided regarding the upstream water flow did not match the downstream observations. “The water has to be going somewhere,” he says. Ordering the observers to new locations, he found that the St. Vrain had breached its banks and was heading their way. He quickly mobilized the emergency teams and was able to begin evacuations four hours before the flood hit Longmont.

“If the data isn’t making sense, trust your instincts,” concludes Rademacher. It helps if your instincts are honed by years of professional training and observation.

Credit: City of Loveland
Deliberately located in the floodplain, the Loveland fairgrounds took heavy damage when the Big Thompson River breached its banks and cut three channels through the city, growing to a mile wide in places.

Lesson #2: Use Social Media for Education and Alerts
Flood’s coming. How to get the word out?

In a program originally tested during the 2012 High Park Fire, Fort Collins made extensive use of social media, particularly Facebook and Twitter, along with message alerts to both inform and alert citizens. During the flood, the city’s Facebook page received 179,000 hits and in three days engaged over 68,000 individuals in a populated area of 150,000. As a result, “Very few phone calls came in,” says Brian Varella, Fort Collins floodplain administrator and chairman of CASFM. The use of social media was credited with the smooth evacuation of three small neighborhoods whose residents were waiting when the police and the evacuation buses arrived.

“We can’t address flood risk in the future like we did in the past,” observes Varella. He stresses the need for strongly worded “actionable language.” He believes that it is human nature to discount risk and forget common history. For effective current communications, he notes, “a standard sound bite has gone from six seconds in Edwin R. Murrow’s day to less than one second in our time.”

Similarly, Kurt Bauer, Boulder’s engineering project manager, is working to re-engage the public about the potential of flash floods and the next likely event. He is stressing the motto “Climb to Safety.” Boulder once distributed an informational flyer to every address in the floodplain. Four months later, a survey found that 70% of the residents were still unaware that they lived in a floodplain: thus the need for ongoing education. “With our creeks, we don’t have a lot of time,” he says. His advice to other managers is “Get the word out.”

Bauer works especially hard to get the word out that people should not drive in a flood. At least 80% of the storm deaths occurred because of someone attempting to drive through floodwaters. He says that much of what worked in Boulder was because of the city’s very robust flood preparedness and outreach programs. “[Our education efforts] probably saved lives and mitigated impacts,” he says.

Lesson #3: Training and Rehearsal Pay Off
Although getting the word out in time of emergency is obviously necessary, it also pays to have been training and rehearsing for such an event.

In Loveland, Gingery says, extensive planning, training, and rehearsal paid big dividends. Within the previous year he and several members of his staff had attended specially designed Federal Emergency Management Agency (FEMA) classes in Maryland, training for the possibility of simultaneous flooding on both the Big Thompson and the Poudre rivers, a simulation that proved close to the actual flood experience. Somewhat surprisingly, FEMA’s own statistics show that “95% of communities experience what they train for.”

Gingery also credits FEMA with great accuracy in its floodplain designations. He shows an aerial photo of the actual flood overlaid with FEMA’s predicted 100-year floodplain outline. It is virtually an exact match.

For Estes, Birchfield frequently trains with police and firefighters for wildfire protection. It’s a small but tight-knit group of men who are neighbors, friends, and disaster managers.

In Fort Collins the previous spring, because of the extensive fires that had occurred west of town, managers concerned about debris, flash flooding, and landslides held a training exercise to simulate just such a flood. That exercise was especially useful in honing interdepartmental communications. As a result, says Fort Collins floodwater engineer Chris Lochra, “we now have very little hesitancy in deciding what we need to do.”

Isn’t that what training is all about?

Credit: Ayres Associates
Images delivered in real time helped emergency managers become rapidly informed of conditions, such as the river breaching and road fl ooding visible in this view of the Big Thompson River.

Lesson #4: “If You Build It, It Will Work”
Referring to earlier capital improvements, and deferring any personal credit, Loveland’s Kevin Gingery says simply, “Loveland is also a success story [relative to the flood] because of the foresight, planning, and execution of our forefathers over many generations. Our forefathers did some great planning to keep people out of harm’s way.”

And in Longmont, along Left Hand Creek, bridge work and a major rechanneling project near a trailer court and the wastewater plant were completed earlier in 2013. Both the trailer court and the wastewater plant were protected from what proved to be a 100-year event on that creek. Initially, the Left Hand Creek project had been a tough political fight, but after the flood it paid many dividends in public opinion. Rademacher draws the conclusion, “If you build it, it will work.”

Where Longmont hadn’t been as well prepared was along its other river, the St. Vrain. “Over many years our department and the city council and others involved had talked a lot about the improvements needing to be made,” says Rademacher, but they never were. The political will was simply not there. Along the St. Vrain, Longmont sustained damages estimated at $152 million. The political will changed.

“At heart we are a great community that sticks together,” says Rademacher. As evidence he mentions how the city had recently purchased the inundated mobile home park, paying pre-flood flood values. “Those people had already been traumatized enough,” he says, “and we as a community wanted to help them, and also move quickly with the cleanup and restoration.” Unfortunately, several other towns and cities affected by the flood have been drawn into litigation over land values and restoration needs.

“If you’re there for people in their time of need,” says Rademacher, “They will stand behind you when you move forward.” When he recently went to the city council to request increased fees, the council voted to allot more than what he asked.

Fort Collins, inspired by an earlier flood, had also recently made capital improvements to its floodplain, including two large levees and two engineered outflow diversions. All these worked as planned, although Fort Collins did suffer about $1 million in damages, relatively minor compared to other cities. Varella credits this to “a nice mixture of prior planning, measured response, and plain dumb luck.”

Part of the “dumb luck” was that two reservoirs on the North Fork of the Poudre were low and took a great deal of water before they began overtopping. Fort Collins is currently building another outflow into a large natural area.

On the other side of the coin, what wasn’t built didn’t work. In Boulder, officials had wanted to work on the many small drainages and ditches that are vital for quick conveyance. Because of budget restraints, this work had been put off. Not surprisingly, according to Bauer, “drainages that weren’t worked on had the most damage.”

The list of damages caused by projects up and down the Front Range that had been previously seen as necessary but had not gone forward is a sad one. Again, total damages for the flood were estimated to be over $3 billion.

Credit: City of Loveland
Residents of Loveland look over a railroad embankment that washed out when the Big Thompson River fi lled gravel ponds, which then breached and cut a new channel around the north side of the town.

Lesson #5: Anticipate New (and Old) River Channels
In almost every affected city, most of the damage occurred outside of the designated floodplains, often because the rivers breached their channels and cut new ones. The St. Vrain abandoned its channel in at least 10 places between its headwaters above Lyons and its confluence with the South Platte River. Numerous bridges were severely damaged or lost because of scouring. Other bridges had their capacity reduced by deposition of material scoured out further upstream. In Estes Park, Birchfield saw 4-foot-diameter boulders, which had been in place for many decades, “just disappear” on their tumbling journey to the plains.

The Colorado Department of Transportation (CDOT) learned a hard lesson in a hard way. Because almost all east-west roads through the mountains in Colorado run up steep-walled canyons, the question of how best to build the roads and where to put them is in itself a “100-year issue.” Having extensively rebuilt the Big Thompson road west of Loveland after a disastrous and deadly 1976 flash flood that claimed the lives of 136 people, the department discovered after this recent flood that sections it had rebuilt and elevated with riprap and fill were often the first to be scoured out. Many homes built even 50 or 60 feet above water level were lost because their foundations had been scoured out.

Because of this, CDOT revised reconstruction fundamentals. The department has been forced to blast away large portions of mountainside to relocate roadways above the 100-year mark. Many of the large stone blocks blasted from the hillside have been moved streamside as part of 12-foot-thick masonry-like structures to protect the banks. Built at great expense, the new roadways will rest on solid bedrock. The days of riprap for canyon roads are fading.

In Loveland, Gingery notes that in many places, the river channel has gone from being 50 yards wide, to 200 or 300 yards wide. In Longmont, the St. Vrain went from one to three channels, and in places became a mile wide. The Denver Post noted that in places the St. Vrain bike and walking trail, which had been 20 years in the making, “is now a trail without a stream.”

A large number of irrigation head gates, flumes, and diversion structures were also lost to erosion caused by the flood or were left high and dry when the rivers “revisited previous channels,” as Gingery puts it. In response to the widespread damage, state legislators passed a bill allowing the relocation of diversion structures without first having to apply for permission from the Water Court.

Lesson #6: Don’t Overlook Ditches, Dams, and Gravel Beds
Boulder’s David Gochis stresses that one of the most important lessons to emerge from the storm may be the need for better ditch maintenance and management. “That stuff’s not really in the floodplain mapping exercise,” says Gochis, “so a key lesson is to incorporate ditches into the projections.”

Ditches became silted up or blocked with debris. Boulder has hundreds of miles of small ditches and has identified some 200 debris dams blocking them. The city has received a conditional FEMA grant of $10 million to $14 million to remove the debris dams. In the wake of the flood, Boulder found that some of the mapping done in the 1980s was inaccurate. Using extensive pre-and post-flood aerial mapping, the city has identified two drainages and three creeks that need to be remapped. These have been updated to identify where spillage would go.

Jeff Arthur, Boulder’s director of public works for utilities, notes that for “thunderstorms where they are predicting a small amount of water that would not have caught our attention in the past, we’re paying more attention.”

In Fort Collins, a local ditch company may have prevented the flooding of three neighborhoods and the destruction of a bridge when it diverted about 15% of the Poudre River’s flow into its channels. With an average annual flow of less than 200 cubic feet per second (cfs), the Poudre peaked during the storm at over 10,000 cfs at the mouth of the canyon, according to hydrologist Beck Anderson. However, flow in the city itself was measured at 8,900 cfs. For this and other obvious reasons, Varella urges, “In the future, during a flood, ditch managers should be present in the command center.”

Credit: City of Loveland
Aerial view of Rossum Drive in Loveland, CO, which had been designed to be overtopped. The site includes installation of both low- and high-level automated alarms, which triggered a well-rehearsed emergency plan.

Another major help to stem the flow were numerous gravel beds along the Poudre, which helped absorb the force and volume of flow. However, the gravel beds along the St. Vrain in Longmont were less useful. The “missing water” that Dale Rademacher recognized “had to go somewhere” had spilled into gravel beds along the river. But these had not been designed to spill back toward the river. Instead, they spilled and broke away from the river and in the process knocked out a railroad embankment and created a new channel that outflanked the northern edges of the city’s defenses.

Within two days, six small dams along the Front Range were blown out and many reservoirs overtopped, including a dozen in Boulder County alone. In Larimer County, five small dams had a cascading failure, killing one person. At a recent CASFM conference, Bill McCormick, head dam safety engineer for the Colorado Division of Water Resources, concluded that in the past dam safety and floodplain management rarely intersected and that there is a need for safety managers and flood plain managers to communicate more. Recommendations included creating dam failure inundation maps, creating warning systems for communities downstream of dams, and more coordination with dam owners.

He summed up what worked and what didn’t: “Dams designed to withstand 100-year floods stayed sturdy,” he said. “Low-hazard dams designed for 25- to 50-year floods broke.” He also urged people to be alert for damage to the hundreds, possibly thousands, of small earthen dams dotting the Colorado landscape, many of them too small to qualify for state safety inspections.

Lesson #7: Communities Must Own or Control Their Floodplains
For good reasons, many if not most communities grew up close to the rivers, and particularly at the confluence of rivers. Thus, floodplains are often the historical heart of a community. Loveland was fortunate in that it had been founded on higher ground. The forefathers that Gingery cited had acquired large areas of bottom land and began placing natural areas, parks, trails, and the city golf course in the floodplain.

In Fort Collins, the city currently owns two-thirds of the 100-year floodplain, after decades of steadily buying up floodplain parcels. Tight regulations with special restrictions are in place for the remainder of the land. Fort Collins constantly works to acquire more land, pursuing a “willing buyer/willing seller” approach. Now, with almost full ownership of the plain, the city is working on a large new outflow project, removing an obsolete diversion structure and re-engineering the river along a 2-mile corridor that runs through the center of town.

Boulder has a historical problem in that the city was first settled by miners at the mouth of the nearby canyon and straddling the creek. As the city bought up floodplain, it occupied it. Boulder’s library and city hall, police headquarters, Boulder High School, the university’s married student housing and research campus, and the city-county court complex are all built in flood hazard areas. Naturally, controls are tight; Boulder even has its own special designation of High Hazard Zone.

By contrast, 20 miles to the east, the Weld County Board of Commissioners and the city of Evans both were forced to declare emergency disasters because of damage to structures in their floodplain. The crest of the South Platte reached a record high of 19 feet, surpassing by more than 58% the prior crest record of 12 feet. The Poudre River peaked at 7 feet. More than one hundred homes on the east side of Greeley were underwater. Mobile home parks had extensive damage. As many as 1,000 public school students were displaced. Nearby Evans lost two mobile-home parks, which were so devastated that they may need to be condemned to eliminate the health hazards posed by contaminated flood debris. The wastewater treatment plant was knocked out, requiring an estimated $14 million in repairs. The nearby town of Milliken, sitting at the junction of the Little Thompson and the Big Thompson, also lost mobile home parks, and 43 homes were destroyed.

Far to the east, Nebraska officials braced for the onslaught of debris and contamination. Fecal matter from washed-out sewage plants was their primary concern.

Lesson 8: Secure the Oil Tanks
Greeley is located in the midst of large oil- and gas-producing fields. During the flood more than 1,900 wells were affected by flood waters. Although no wellheads were damaged, the storage tanks were heavily affected. An estimated 43,00 gallons of oil were spilled and many tanks toppled. Approximately 2,600 wells were shut down during the flood. Three hundred of these remain shut down.

Across the state, Colorado has more than 5,900 oil and gas wells within 500 feet of rivers or streams. That number rises to as many as 20,850 wells when the state includes drainage areas that are normally dry but can fill with water after a storm. The Colorado Oil and Gas Conservation Commission, in its “lessons learned” report, urged the adoption of regulations that would ban underground fuel storage pits, require wells be equipped with devices that can shut them down remotely, and ensure that all storage tanks be securely anchored to prevent them from toppling in floods. The commission noted that in this storm peak flows in the oil fields did not approach the magnitude experienced in earlier floods. Nevertheless, it cautioned, “Equipment that fared well in the September 2013 flood might not do as well in a flood of historic magnitude.”

The devastated town of Lyons, at the confluence of the North and South St. Vrain rivers, had all incoming and outgoing roads cut off for up to two weeks. Floating debris helped knock out bridges and contributed to channel breaching. This town and other nearby mountain communities became the scene of the greatest aerial evacuation since Hurricane Katrina.

Lesson #9: Insurance Is Important
CASFM found that more than 51% of damages to private property were on parcels located outside a designated floodplain. In Colorado, the “mile high state,” with mountain peaks over 2 miles high, only 22,000 homes and businesses have flood insurance, according to FEMA. Most of those policies are for residential properties.

In Boulder, Bauer notes, “There is real confusion in the public thinking that you can only buy flood insurance if you are in the floodplain,” though this is not the case. He says that because of the 30-day waiting period before for such policies take effect, people should buy flood insurance now, ideally including coverage against sewer backups. Boulder and Longmont both experienced many sewer backups, both in businesses and in private residences. Bauer suggests that the public might also explore installing backflow prevention devices for their sewer connections.

The Denver Post reported that Colorado policies under the National Flood Insurance Program had increased by 1,648, or 7.7%, between 2012 and 2013. Not surprisingly, The Post reported, “September’s floods set off a wave of calls, quotes and applications.”

The city of Boulder, one of the hardest hit, added the most new policies, with a 20.1% increase. FEMA reports that Boulder County has 4,779 flood insurance policies in place, but more than 77,000 detached single-family homes. In Boulder itself, about 15% of the population of 300,000 resides in the floodplain. In the Greeley area at the end of 2013, only 153 residents across the entire Weld County had active flood insurance policies in place.

The Coming Spring Runoff
The obvious next challenge for floodplain managers along the Front Range, especially those still recovering from last fall’s big storm, is preparing for the coming spring runoff. Brian Varella sums up the biggest fear: how might cities best plan for the possibility of an early season heat wave that dumps tropical moisture at high altitude upon a heavier-than-normal snow pack when the soil is already saturated and the reservoirs are full?

Obviously, the daily work of stormwater planning and preparation continues.

Dale Rademacher takes the possibility with a smile and points out that the state experienced a serious flood in 1995 even though the snowpack was only 73% of average. “You just do what you can do and accept what comes.”

Keith Sheaffer, CDOT’s chief of operations for flood recovery efforts, observes that every spring communities experience the equivalent of a 25- to 50-year rainfall event even when “it’s just a normal spring runoff.”

Demonstrating the power of the flood in Loveland, Gingery was out marking new high-water marks when he found a motel key from Estes Park. It had traveled more than 30 miles and descended more than 2,500 vertical feet. In the Big Thompson Canyon, Estes’ Birchfield found a 1930s-era silver coin, probably from someone’s washed-out collection. He carries it with him as a symbol and reminder of the people’s losses. “Our rules were made to serve the people,” he says. “So in the end, it’s not about the rules, it’s about serving the people.”

Again, and still, the daily work of stormwater planning and preparation continues. 

About the Author

Bear Gebhardt and Stephen Johnson

Bear Gebhardt and Stephen Johnson are long-time journalists, with credits in many regional, national, and international publications. Gebhardt is also the author of seven

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