2013 Floods: Rebuilding Boulder Open Space

For four days following Wednesday, Sept. 11, 2013, floodwaters and persistent rainfall prevented Open Space and Mountain Parks (OSMP) staff from cataloging the full extent of the flood's damage. Finally, when the rains began to subside on Monday, Sept. 16, OSMP staff assembled in a small conference room. A map of the entire trail system, separated into dozens of zones, lay on a table in front of them.

Teams of two to three staff members were tasked with hiking all trails in their zone to catalog the damage, identify the likelihood of whether major or minor repairs were needed, and determine whether trails were safe and passable for the average visitor. When the assessment teams returned, the damage to open space and its effect on the community and OSMP became clear: It would take years for the city’s open space system to rebuild from the historic flooding.

Recognizing that community members needed a space to heal from the floods, OSMP prioritized trail repair work that would reopen popular trails to help as many people reconnect with the land – as fast as possible.

By September 30, 2013, the department began reopening significant sections of several major trails. Then, week after week, the department opened more and more trails. By November 1, 2013, the department had reopened 108 miles of trails – or about 75 percent of its 145-mile trail system.

Throughout the fall of 2013, OSMP staff trail crews – and teams of generous volunteers – conducted significant repairs on important open space trails, including the Bear Canyon, Skunk and Bobolink trails. Smaller repair projects on the Goat and Fern Canyon trails and several others helped visitors reconnect with OSMP’s dramatically changed open space system. By the end of 2013, the department was able to reopen 95 percent of its 145-mile trail system. However, significant flood repairs still loomed.

When OSMP completed its initial damage assessment, the department knew it would have a long recovery process ahead of it. Recognizing the scope of the rebuilding efforts, OSMP established flood recovery as its top departmental priority and focused its rebuilding on infrastructure that was eligible for reimbursement from the federal government, such as Chapman Drive, the NCAR-Bear Canyon Trail, the Shadow Canyon South Trail and important Mesa Trail sections.

Floodwaters completely eroded about 30 to 40 feet of the Royal Arch Trail, creating a massive trail gap in the popular Boulder trail. Recognizing the trail’s importance to visitors and the climbing community, OSMP and the Front Range Climbing Stewards – a trail-building partnership between two Boulder-based nonprofits, the Boulder Climbing Community and the Access Fund – worked together to complete repairs along the path. That work, assisted by volunteers, included the construction of a new route around the trail section that was destroyed during the 2013 floods.

The September 2013 floods caused significant damage in the area. To address the damage, OSMP trail crews began to repair a landing platform that provides visitors a view of the falls and completed additional repairs in the area. As OSMP crews conducted their work, they recognized the need for additional rebuilding work, such as more substantial repairs to the gabions, which are rock baskets used to catch sediment from the hillside. Unfortunately, those repairs would necessitate extended closures in the area.

In 2018, the department rebuilt the gabion walls and conducted additional repairs to stabilize the Boulder Falls trail. OSMP reopened the iconic Boulder area in June of 2018.

Floodwaters caused extensive damage to trail tread and carved large gullies along the path. In 2015, OSMP completed improvements along the trail, which included better connections to existing paths on Mount Sanitas and enhanced drainage features that will make the trail more resilient and less prone to erosion damage. OSMP also completed numerous other flood repairs, including fixing large trail gullies. Volunteers also helped complete repairs along this popular path.

Chapman Drive, constructed by the Civilian Conservation Corps (CCC) during the Great Depression in the 1930s, sustained significant damage along 2.6 miles of the road, which is used as a recreational trail and vehicle access for administrative and emergency purposes. Damage included erosion ruts more than 4 feet deep in some places, along with landslides that removed sections of the road and destabilized nearby slopes. The floods also destroyed the trailhead parking lot when Boulder Creek jumped its bank.

OSMP’s repairs along Chapman Drive fixed significant trail damage and included additional infrastructure, such as replacing seven culverts, to address water drainage along the trail. All of the work was completed to match the historic CCC design and construction of the road while making important drainage improvements for sustainability. This work has helped improve visitor experiences on the trail while providing emergency vehicles an alternate access road to and from Flagstaff Mountain.

The flood caused erosion damage along the Shadow Canyon South and Mesa trails near the South Mesa Trailhead. The erosion damage was a few inches to 3 feet deep in some places. To repair the damage, OSMP filled in erosion ruts with soil excavated from new roadside drainage ditches.

The Shadow Canyon Creek crossing was hardened with stone to prevent significant wash-outs. OSMP also made drainage improvements to reduce the likelihood of substantial road damage in future flood events, including adding more than 5,100 feet of side ditches and 46 rolling dips. Those features will collect water from the road and adjacent slopes, diverting it from the road. This work fixed 2.25 miles of trail, which can now be used for vehicle access, including OSMP administrative needs, emergency responses and utility access.

The flood caused erosion damage along the Shadow Canyon South and Mesa trails near the South Mesa Trailhead. In some places, the erosion damage was a few inches to 3 feet deep. To repair the damage, OSMP filled in erosion ruts with soil that was excavated from new road-side drainage ditches.

The Shadow Canyon creek crossing was hardened with stone to prevent significant wash-outs. OSMP also made drainage improvements to reduce the likelihood of major road damage in future flood events, including the addition of more than 5,100 feet of side ditches and 46 rolling dips. Those features will collect water from the road itself along with adjacent slopes, diverting it away from the road. All told, this work fixed 2.25 miles of trail, which can now be used for vehicle access, including OSMP administrative needs, emergency response and utility access.

The surface material covering the trail washed away during the floods. The trail next to the bridge crossing Four Mile Creek was also washed away when the creek jumped its banks. OSMP re-graded the trail and surfaced it with crusher fines, which is a gravel product. OSMP also gently sloped the trail to allow water to drain off its surface. OSMP also made several other repairs, including:

• Adding 1,430 feet of trail-side ditch to collect water from the trail surface and adjacent slopes.
• Adding 12 rolling dips to divert water from the trail and trailside ditches.

The floods caused extensive damage to trails on Shanahan Ridge south of the National Center for Atmospheric Research, with floodwaters cutting ruts 5 to 6 feet deep in some places. The floods also damaged water features along Shanahan-area trails used for emergency vehicle access. To repair the damage, OSMP resurfaced portions of the trail, replaced existing drainage features and added new ones.

The 2013 floods destroyed bridges that crossed the Doudy Draw, Skunk Canyon and South Boulder Creek trails. After completing extensive permitting, OSMP rebuilt new bridges that are more sustainable and less likely to be a complete loss in the next flood.

The 2013 floods damaged infrastructure that helps drain water from the area and off trails. Floodwaters also caused extensive trail tread damage, with floods cutting gullies 2 to 3 feet deep in some trail areas. The McClintock Bridge also sustained significant damage and needed to be repaired. When the floods subsided, OSMP immediately focused on repairs in the Chautauqua Meadow area. In time, the department began work on larger recovery projects, including repairs to the Chautauqua Trail and the McClintock Bridge.

To make the Chautauqua Trail more sustainable for the future, OSMP repaired the path with some slight alignment changes and repaired culverts and side swales to improve drainage and minimize trail erosion. Repairs to the Chautauqua Trail also featured a re-surfaced trail tread that will allow visitors who use wheelchairs to access one of two gathering areas that have provided generations of visitors breathtaking views of the Flatirons. The project also included restoration and revegetation of areas along the Chautauqua Trail.

The 2013 floods ripped the Gregory Canyon Road apart, making it impassable. The Amphitheater Trail bridge over the creek was buried entirely under flood debris at the trailhead. In June 2015, OSMP completed repairs to the Gregory Canyon access road and trailhead, completely rebuilding sections of the road ripped apart by the floods. In 2017, OSMP raised the Amphitheater Bridge to a minimum height required by Boulder County, which will help make the bridge more resilient. OSMP also installed stacked stone abutments to provide more protection from high-water levels.

OSMP worked with community partners to help restore areas disturbed by the floods. In 2015, the Environmental Protection Agency lauded Seth Blum, a Boulder teen, for his work to help restore a riparian area near South Boulder Road and South Boulder Creek. That work, guided by OSMP’s ecological staff, restored 25,000 square feet of habitat and included the planting of 1,000 native plants, shrubs and trees.

Every June and August since 2014, the department has monitored Preble’s Meadow jumping mouse, a federally threatened species. Trappings and data collected by OSMP indicated the animal species remains in sensitive OSMP habitats following the floods.

In 2017, OSMP completed a major restoration project that repaired damage from the 2013 floods by returning Boulder Creek east and west of 61st Street to its pre-flood channel. The project also improved native fish habitat in Boulder Creek and restored natural areas surrounding the creek. It also included the planting of more than 11,000 native trees and shrubs. This will help improve the creek’s sustainability and resiliency and help mitigate damage to private and public property during future floods.

When Open Space and Mountain Parks staff assessed the trail system on Sept. 16, 2013, they noted that trails built with sustainable trail-building principles weathered the floods with little to no damage. These principles, which OSMP has been utilizing and honing for years, require extensive collaboration between trail specialists, planners, wildlife, plant and wetland ecologists – and at times – engineers and landscape architects. The key goal of sustainable trail building is to minimize trail erosion by ensuring water drainage. This is done by:

• Having minimal 8-percent grades that greatly reduce trail erosion. Steeper trail grades allow water to gain volume and velocity, which increases erosion potential.
• Building grade reversals, which are trail segments where an ascending trail will descend for a few feet, then return to ascending. This creates low points in the trail that forces water off of it.
• Building outslopes, which are sections of trail that tilt slightly downward and help the trail drain water off of it.