Longmont flood recovery prepares for future storms through innovation

With the continued work on the St Vrain Greenway, Longmont has turned a tragic flood into an opportunity to improve the city’s main waterway, benefiting the environment and people around it.

Starting September 11, 2013, Longmont experienced record breaking rains. According to the National Centers for Environmental Information, the average precipitation for Colorado in 2015 was 17 inches annually. In one 24 hour span, more than nine inches fell.  Over ten days the residents saw more than 17 inches of precipitation, leading to devastating flooding throughout the northeastern quarter of Colorado.

The St Vrain Creek basin flooded, with an estimated $100 million in flood related damage in Longmont alone. Eighteen counties in Colorado were harmed by the flood, with 120 miles of state highways, 76,000 homes and 750 business damaged and ten confirmed fatalities. The result was over $4 billion in damages across the state according to FEMA and the city of Longmont. 

Whole sections of Longmont were cut off from each other as property, roads and paths were washed away. Longmont’s Sunset Campus for Parks and Natural Resources, across from Izaak Walton Pond, was underwater, as well as sections of major streets like Hover Road. Water rushed across the ground in torrents. The levy that separates Izaak Walton Pond and St. Vrain Creek was washed out almost entirely. 

Higher up in Longmont’s watershed, the Ralph Price Reservoir and Button Rock Dam were contaminated with debris that threatened further damage should it block the dam’s spillway. Colo. 80, also known as Longmont Dam Road, was washed out in sections that made even initial damage assessment by emergency responders hazardous and life-threatening.

The 2013 Flood has been referred to as a 100-year flood, though not necessarily due to frequency. Instead it refers to the probability that a storm or rain event could happen. 

“A 100-year storm event is a flood that statistically has a 1-percent chance of occuring in any given year,” said Josh Sherman, Senior Civil Engineer for the city of Longmont. 

The state of Colorado evaluated drainage for St Vrain Creek after the flood and determined the water flow during the storm had  increased 150% through Longmont. Accommodating the higher water flow  became one of the starting goals of the Resilient St Vrain Project, or RSVP, resulting in approximately 500 structures and 400 acres of land being removed from the 100-year floodplain due to channel improvements, according to Sherman.

The Resilient St Vrain Project is the city’s master plan for the channel improvements. The total cost for RSVP has been estimated to $140 million, from the city’s website. Longmont has secured funding for the work, including the completed projects, up to S. Sunset Street and the completion of Izaak Walton Reach 2, totalling half the projected budget. 

“Generally FEMA funds 75% of the disaster cost and the local agency (i.e the city) is required to provide or match the remaining 25%. For the 2013 Flood recovery, the state has committed to providing half (12.5%) of the local agencies’ match,” said Rigo Leal, public information officer for the city of Longmont.

“The city has been able to maximize funding to continue to move the project further upstream than originally expected,” Leal explained.

Other sources of funding have included a $20 million voter approved storm drainage bond, FEMA disaster recovery and Colorado Development Block Grant Disaster Recovery from the Department of Housing and Urban Development. Competitive bidding by local contractors resulted in costs below the estimated budget for each phase of the project, making more room for the city to operate with financial efficiency, according to Leal.

Dickens Farm Nature Area is one of the more noticeable and noteworthy additions, having earned an award from the Colorado American Public Works Association for 2020 Best Trail/Park Project.

Dickens Farm is noteworthy, not just for its access to recreational activities, but for the ecological considerations as well.

“Prior to the flood there was an eight to ten foot tall irrigation structure across the creek. The structure created a barrier to fish passage upstream,” Leal said.

The structure was destroyed in the flood and the city worked with the ditch company to relocate the diversion downstream. Drop structures —man made structures designed to control the speed of the water  — were constructed in the creek corridor, allowing for fish to pass up and downstream. Areas, where rocks were used to stabilize the creek banks, were buried and covered with native seeding and planting to provide a better wildlife habitat in the channel.

The prime operation for the section is relocation of a sanitation line that crosses St. Vrain Creek near Left Hand Brewing Company’s tap room. 

The U.S. Army Corp of Engineers, or SUSACE, has partnered with the city to work on Izaak Walton Reach 2. The final designs have been completed, along with the USACE feasibility studies, and construction is set to begin by late 2021. This section of work will be overseen by the USACE, and includes the replacement of the Boston Avenue bridge and improvements to the channel and levy between Izaak Walton Pond and the creek.

The city has completed a conceptual level design for City Reach 3, which would encompass the area from Sunset Street to Airport Road. Plans and design information are available on the city’s website. In order to secure funding options, a proposal has been submitted for a FEMA Building Resilient Infrastructure and Communities grant.

The first upstream improvement in City Reach 3 is the section between Sunset Street and Hover Road, referred to as Hover Road Reach. According to Sherman, the preferred design is a split flow channel from Lykins Gulch to Fairgrounds Pond and a new bridge at Hover Road approximately 1800 ft south of the current bridge that crosses the creek. That phase is estimated to cost up to $20 million.

Though likely that City Reach 3 won’t see completion until 2025 or later, each phase completed makes Longmont a safer place should another statistical improbability occur.