The September 2013 flooding in Rocky Mountain National Park washed out a section of the Twin Sisters Trail. Park staff have received approval to reroute and repair the trail/NPS file photo

It took three-and-a-half years, but Rocky Mountain National Park officials in Colorado have received the go-ahead to conduct repairs and rerouting to two trails that were heavily damaged by torrential rains and floods in September 2013.

Sue Masica, director of the National Park Service's Intermountain Region, recently signed off on the plan for the work. 

Following the September 2013 flood, park staff prepared an environmental assessment to evaluate alternatives and the potential impacts associated with reestablishing five trails that were badly damaged during the flood: Twin Sisters, Aspen Brook, Alluvial Fan, Ypsilon Lake, and Lawn Lake. The purpose of the EA was to identify potential travel routes while protecting natural and cultural resources and preserving wilderness character.

A decision to reroute and repair the Lawn Lake, Ypsilon Lake, and Alluvial Fan trails was previously made, and a finding of no significant impact was signed for those three trails last June. Park staff deferred the decision on the reroutes and repairs to the Aspen Brook and Twin Sisters trails until 2017. A description of the selected action for the Aspen Brook and Twin Sisters trails follows.

Aspen Brook Trail - The trail will be rerouted and repaired. Abandoned sections of the existing trail (about 3,360 feet) will be stabilized and revegetated. This work is expected to take a number of years to complete. During the trail construction, some areas may be temporarily closed to hikers. This trail will remain closed to equestrian use for the duration of the project. A new trail extension to provide a connection to Spur Highway 66 outside the park is a second element of this decision and has additional requirements.

Twin Sisters Trail - The informal foot trails that have developed across the landslide and south of the landslide will be retained and maintained to the extent practical. The informal foot trails will be incorporated into the regular trail maintenance program, and repairs and erosion-control measures to mitigate impacts will be implemented. Existing trail segments or informal routes that are redundant or obsolete will be stabilized and revegetated. The steep trail grade, limited width, and limited clearing limits of the informal foot trail on the south side of the landslide does not accommodate equestrian use; therefore, only pedestrian use will be allowed on the Twin Sisters Trail.

Once these Twin Sisters Trail repairs and erosion control measures are completed, the park will monitor trail conditions over time to determine if repairs are adequate and sustainable. If repairs are not sustainable, the park may seek funding to construct a trail reroute.