San Juan National Forest
U.S. Forest Service
15 Burnett Court
Durango, CO 81301
September 4, 2018
WESTON PASS POST-FIRE BAER ASSESSMENT REPORT SUMMARY
The Weston Pass Fire started on June 28, 2018, and is located primarily on the Pike National Forest (NF), within the Mosquito Range near the town of Fairplay, Colorado. The area is characterized by low to moderately steep terrain including dissected basins with one enclosed park. As of June 22, the fire burned 14,182 acres of Forest Service System (NFS) land, 22 acres of Bureau of Land Management (BLM) land, 54 acres of state land, and 689 acres on private land. Dominant vegetation types within the NFS burned area are primarily composed of a mix of montane and subalpine forest vegetation such as quaking aspen, lodgepole pine, ponderosa pine, mixed conifer, and grassland/forb/shrub.
The Weston Pass Fire burned area was surveyed and assessed by a Burned Area Emergency Response (BAER) team comprised of Forest Service scientists and specialists. The Forest Service is responsible for addressing risks on NFS land. The BAER team evaluated the burned watersheds to determine post-fire conditions, and identify values-at-risk such as threats to human life and safety, property, and critical natural and cultural resources. In addition to these critical values, other threats were also assessed, such as the risk for increased post-fire flooding, sediment flows, rock slides, hazard trees and noxious weed spread. Proposed emergency stabilization treatments are recommended by the BAER team which reduce these potential threats.
The BAER assessment team’s analysis of the burned area and recommended emergency treatments are documented in a Forest Service (FS) Burned-Area 2500-8 Report. This report was submitted to the Regional Forester for the Rocky Mountain Region (Region 2) by the Pike and San Isabel Forest Supervisor for review and funding. The BAER report also provides relevant information that is shared with its inter-agency cooperators to help identify potential threats to lands downstream of the fire.
The following is a summary of the BAER team’s burned area assessment for the Weston Pass Fire:
8 sub-watersheds of the South Platte basin were analyzed and modeled to compare pre-fire conditions to post-fire predicted response: Chicken Dip, Pony Park, Buffalo Creek, CR22-1, CR22-2, CR22-3, Antero Main Stem, and Rough and Tumbling.
There are approximately 3 miles of perennial streams, 44 miles of intermittent streams, and 36 miles of ephemeral streams.
There are approximately 23 miles of National Forest System (NFS) roads, and 1 mile of NFS non-motorized trail.
There are 1,038 acres with high hazard ratings for soil erosion, 461 acres with moderate hazard ratings for soil erosion, and 12,180 acres with low hazard ratings for soil erosion. Elevated soil erosion hazard is only applicable for the first few years following the Weston Pass Fire - until revegetation occurs to stabilize the slopes.
There are about 7,241 (51%) acres of unburned/low soil burn severity, 6,253 (44%) acres of moderate soil burn severity and 689 (5%) acres of high soil burn severity.
Soil burn severity is the fundamental indicator used to evaluate post-fire conditions. The soil burn severity categories reflect changes in soil properties from pre- to post-fire and are a key element used to identify post-fire threats. The distribution of unburned, low, moderate, and high soil burn severity levels become a baseline for resource specialists to monitor changes in soil-hydrologic function and vegetative response as the burned watersheds recover.
High and moderate soil burn severity categories have evidence of severe soil heating and the consumption of organic material; the soil seedbank and water infiltration characteristics are reduced. Natural recovery is slower where little or no vegetative ground cover remains, with increased surface water runoff resulting in increased soil erosion. Areas of moderate soil burn severity have viable roots and some soil cover, but may still be vulnerable to erosion on steep slopes. The low to very low soil burn severity areas still have good surface soil structure, intact fine roots and organic matter, and should recover more quickly once revegetation begins and soil cover is re-established.
Strong water repellent (hydrophobic) soil was observed within the moderate to high soil burn severity areas. Hydrophobic soil conditions are common within moderate and high burn severity areas and rare in the low burn severity areas.
Identified Values-at-Risk, Threats, and Emergency Conditions
Colorado summer thunderstorms (monsoons) have the greatest likelihood of generating large runoff and soil erosion events. If large summer thunderstorms occur, the primary values-at-risk within the burned area are human life and safety, transportation infrastructure (roads and motorized trails), cultural resources, and native vegetation communities. The primary threats caused by the fire include 1) increased runoff, which is expected to intensify the first 2-3 years following the fire until the burned watersheds recover, and 2) accelerated hillslope erosion as a result of increased runoff and decreased infiltration rates. High intensity, short duration rainfall may result in downstream flooding and localized debris flows. Additional threats originating from the destabilized hillslopes throughout the burned area include falling trees and debris flows.
Potential impacts on human life and safety, property, natural resources and cultural resources were identified by the BAER assessment team. Forest Service values-at-risk include human life and safety, roads, trails, access to a remote automatic weather station (RAWS), Buffalo Springs Campground, critical habitat for Threatened and Endangered (T&E) species (Mexican Spotted Owl, Canada Lynx, and Wolverine), hydrologic function, recovery of native vegetation due to increased risk for establishment and/or spread of noxious weeds, as well as grazing, historic properties, agricultural pipelines, spring developments, and historic land survey monuments. Non-Forest Service values include human life and safety, municipal water supply, a private reservoir, County Road 22, Highway 285, irrigation ditches, and a stream gauge.
Human Life and Safety: There are high or very high risks to the safety of forest recreating visitors traveling, range permittees, and FS employees working within the burned area. Potential threats exist along roads, trails, at recreation areas, and to permitted uses from flooding with the potential for localized debris flows, falling hazard trees, rock fall, and loss of ingress and egress. Although Buffalo Springs Campground did not burn, it is still at very high risk due to flooding and debris flows from up-slope burned areas.
There is an intermediate risk to recreating forest visitors and FS employees traveling FS Road 432, Trail 631, and all Level 1 roads within the burned area due to the increased threat of flash floods, debris flows, falling rocks, and trees.
There are increased risks associated with flooding and debris flows caused by post-fire conditions to the public traveling on County Road 22 and Highway 285 as well as private residences on the south side of County Road 22 and at the Old 63 Ranch west of Highway 285.
Property: There are high or very high risks to portions of NFS roads (158, 168, 430, 431, 433), and a NFS trail (618) within the burned area from post-fire impacts of increased overland flow, and accelerated hillslope erosion. Impacts include damage to the road and trail surface and drainage features and/or loss of access due to severe erosion of the road surface, or deposition of sediment or debris.
There is a high risk to the infrastructure within Buffalo Springs Campground due to the increased overland flow and accelerated hillslope erosion. Impacts include damage to the vault toilet and potable water hand pump.
There is a high risk to spring developments infrastructure used for grazing water development, decreasing hydrologic function, and negative effecting water quality due to flooding and sedimentation impacts.
There is a very high risk to water delivery pipeline for stock water due to flooding and erosion threats.
There is a high risk to an access road to the Jones Hill RAWS weather station due to flooding and erosion causing damage to the road prism.
There is a very high risk to historic land survey monuments due to flooding, debris flows, and falling hazard trees destroying or covering existing historic stone survey monuments.
There are risks associated with flooding and debris flows to drainage structures on County Road 22 and Highway 285.
There are risks associated with flooding and sedimentation to private irrigation ditches, ponds, and a Colorado State stream gauge located downstream from the burned area.
Natural Resources: There is an intermediate risk to water quality and hydrologic function within Rough and Tumbling Creek.
There is an intermediate risk to suitable-occupied Canada Lynx habitat within the burned area as a result of erosion, sedimentation, wind-fall of exposed tree stands, and loss of understory.
A high risk to native and naturalized plant communities as well as riparian FS treatments due to access to burned areas used by permitted cattle that is caused by the fence-line being burned.
A high risk is anticipated to native plant communities due to the threat from the spread of noxious weeds such as Canada thistle. The wildfire created conditions conducive to noxious weed spread and establishment by reducing competition, and exposing bare mineral soil.
There is a high and very high risk to hydrologic function from increased run-off with overland flow influencing erosion and sediment delivery.
There is a potential threat to domestic water supply off NFS lands due to the close proximity of Antero Reservoir and downstream Spinney reservoir from increased sediment and turbidity, as well as increased peak flood flows which can damage or clog surface water supply intake systems. There is also a potential threat for sediment and debris delivery into Buffalo Springs Reservoir.
Cultural/Heritage Resources: A high and a very high risk is anticipated to critical eligible cultural and heritage resources within the burned area as a result of the loss of vegetation cover.
Emergency Stabilization Treatments
The BAER assessment team’s emergency stabilization objectives for the burned areas are to protect, mitigate and reduce the potential for identified post-fire threats, including increased water run-off flows, soil erosion/sediment yield, loss of road and trail access, introduction and expansion of invasive plant species, and falling burned trees, for:
Human life, safety, and property within and downstream of the burned area;
Forest Service infrastructure and investments such as roads and trails;
Critical natural and cultural resources; and
Native and naturalized plant communities from new noxious weed infestations.
The following post-fire emergency stabilization measures and treatments have been approved:
Implement and monitor temporary area Forest closures to reduce risks to human life and safety.
Install burned area warning signs to caution forest visitors traveling and recreating within the burned area.
Storm-proof and stabilize NFS transportation roads and stream crossings with improved water drainage structures and features to prevent damage resulting from post-fire watershed conditions such as soil erosion, storm water run-off, and public safety hazards to improve the safety of forest visitors and employees. Conduct storm patrol monitoring to ensure stream crossings and road treatments are functioning as intended.
Storm-proof and stabilize NFS trails with improved water drainage structures and features to prevent damage resulting from post-fire watershed conditions. Conduct storm patrol monitoring to ensure crossings and trail treatments are functioning as intended.
Storm-proof campground infrastructure to stabilize vault toilet and hand-pump with sand-bags.
Install slope stabilization measures for pipeline protection, and grade stabilizers for spring collection systems.
Assist cooperators, including local, county, state, and federal agencies with the interpretation of BAER assessment findings to identify potential post-fire impacts to communities and private land owners, domestic and agricultural water supplies, and public utilities (such as power lines, state roads, county roads, and other infrastructure).
Continue to work and coordinate with interagency cooperators, partners, and affected parties and stakeholders.
Continue to communicate risks to the public, community groups, and cooperating agencies.
Provide for cultural resources protection by placing slash at eligible cultural sites.
Conduct early detection surveys and rapid response eradication with herbicide application on noxious weeds along areas disturbed by fire suppression activities, equipment concentration points, high and moderate soil burn severity areas near these fire suppression disturbed areas, and other high priority areas, to reduce the potential for impaired native vegetative recovery and the introduction and spread of invasive weeds.
Provide stone land survey monument protection by installing new land survey monuments where necessary at historic stone monuments, installing erosion control measures to improve the durability and longevity of the monument, and describing and recording monument locations for future use.
Install rock riprap to stabilize existing head-cut and dam outflow, clean spillway culvert and install culvert riser to prevent dam overtopping and potential breach, and install drainage dips along unauthorized road routes acting as water impoundments to minimize effects of cascading dam failures.
SPECIAL NOTE: Everyone near and downstream from the burned areas should remain alert and stay updated on weather conditions that may result in heavy rains over the burn scars. Flash flooding may occur quickly during heavy rain events. Current weather and emergency notifications can be found at the National Weather Service website: www.weather.gov/pub/.