Lava Butte US 97: Restoring Migratory Mule Deer Movement
The Cascades Mountains of Oregon bisect the state north to south. Migratory mule deer summer high in the Cascades, then migrate to winter range in the lower elevations to the east. The well-drained soils of the volcanic formations of the Cascades result in topography unusual in the western states, wherein no major rivers flow to the east for over a hundred miles from Bend to Chiloquin. Thus, no bridges or large culverts are present on US 97, the major highway paralleling the Cascades and perpendicular to the mule deer migratory movement to seasonal ranges. The highway has a very high traffic volume, varying from well over 5000 Average Daily Traffic (ADT) at the lowest volume stretches in the southern part to 20,000 ADT between Bend and LaPine, 30 miles to the south.
The Lava Butte US 97 project is intended to increase capacity of the busy stretch between Bend and LaPine to a projected traffic volume of up to 35,000 ADT. The twinning project divided the highway with a vegetated median of about 150 ft and allowed for two lanes each northbound and southbound.
Previous research indicated that the gentle topography devoid of funneling landscape features (except for the major lava flows at the north end of the project) resulted in no clear ‘hotspots’ where deer concentrated to cross the highway. Instead, deer crossed in a sheetflow pattern. Although deer/vehicle collisions are a problem between Bend and LaPine, records indicate that a major collision area was just south of LaPine, where traffic volume drops dramatically from about 20,000 ADT to around 8,000 ADT. The concern was that as traffic volume increased in the Bend to LaPine stretch, deer and other wildlife were no longer successful at crossing, and winter ranges were being underutilized or overutilized as a result of being forced to remain on one side of the highway. The USDA Forest Service as a cooperating agency in the project required mitigation for the loss of movement to and from seasonal ranges for deer, and other wildlife in the area.
The Lava Butte US 97 project resulted in several new or unusual approaches to mitigation. These include: deployment of an interagency Mitigation Design Team to design and manage natural resource issues on the project; construction of the first large wildlife crossing structures in Oregon, one of which is a combination traffic/wildlife structure; a cost-benefit analysis done by Oregon DOT on the structures; native landscaping on and as far through the underpasses as possible; and management of the National Forest System lands adjacent to the wildlife underpasses to funnel and encourage animal use. Additionally, because of the presence of the Lava Lands Visitor Center at the north end of the project, it was possible to set up an interpretive display to explain the rationale for the wildlife underpasses and their relationship to restoring habitat connectivity.
An interagency Mitigation Design Team was established to work on the Lava Butte US 97 project from project development through construction. The Team met on a regular monthly basis to identify and solve issues as they arose. Regular meetings allowed for issues to be dealt with early and cooperatively. One issue occurred as the DOT transitioned from project design to implementation. USFS agency staff were not funded by the same MOU and an interruption in assistance was possible, yet issues were continuing as construction began. This was resolved and the Mitigation Design Team is continuing as warranted.
Mitigation measures included two sets of wildlife bridge underpasses (two underpasses, one on each set of lanes). The southern set was designed exclusively for wildlife, emphasizing design features for the most restrictive species in the area, which was mule deer. The northern set was unusual because it included accommodation for both traffic and wildlife.
The northern set of wildlife underpasses are unusual because they are designed to accommodate both wildlife movement and traffic. The underpasses were installed primarily to improve safe access for recreational visitors to the Lava Lands Visitor Center, at the far northern end of the project area. The Visitor Center is open only in summer, from Memorial Day through Labor Day, and only during daylight hours. While the road continues past the Visitor Center, traffic is primarily limited to these time periods especially because snow is not plowed from the road during other seasons. Thus, adding an additional ‘lane’ for wildlife in the underpasses adjacent to the traffic lanes provided an extended open area for wildlife at a modest cost over the cost of the traffic function.
Although studies indicate that human use of structures intended for wildlife passage hinder wildlife use, in the case of the Lava Lands Visitor Center structure, several factors argued for the cost effectiveness of providing for both functions. These were the location of the structure near the funneling geographic feature of the lava flow, the modest additional cost to accommodate wildlife, and the temporal separation of human and most wildlife use. Alternatively, a failure to design for wildlife passage would have provided little to no passage opportunities.
The underpasses were designed to accommodate as much native vegetation and structure such as logs and boulders as possible. The orientation of the underpasses almost due north and south allows sunlight to penetrate far into the structures. In the dry, well-drained soils of central Oregon, water is a limiting factor especially under the structures. Drainage was designed to be captured and retained by a deep layer of compost under the structures. The success of this approach will be monitored to see if the passive approach can be adapted in other areas as well. While the basic structure and dimensions of the wildlife underpasses were designed according to current knowledge of effective wildlife passages, the vegetation and rock substrate under the structures were designed by landscape architect to be attractive to humans, attractive cover for animals, and to avoid a fire hazard under the bridge that might adversely affect structure integrity.
US 97 travels through the Deschutes National Forest on this project. The USDA Forest Service agreed to manage the lands adjacent to the wildlife crossing structures so that most animals, especially migrating deer, would be attracted to the structures. Along with the fencing that extends the length of the project area, the vegetation management is intended to assist animals in finding the structures in the absence of guiding topography. A glitch occurred in the agreement to manage vegetation, in that a long-planned vegetation management study area is adjacent to one of the structures. This issue is being handled through the development of a management strategy in an interagency team.
Oregon DOT conducted a project-level cost benefit analysis for the wildlife mitigation measures. Based on the number of deer/vehicle collisions in the area, both from carcass counts and GPS-collared deer mortalities, the benefit to the taxpayer from reductions in collisions was valued at $1.85 for every $1.00 expended on mitigation. This analysis was conservative in that it considered only property damage to vehicles, and a 20-year design life for the structures. No fatalities or major injuries have been recorded in the project area, otherwise the benefit would have been much higher. The value of deer to society was not considered, nor were other wildlife species which would be expected to benefit.
Median was 200’ wide with timber, intended to be visually pleasing in the NM, and also to increase safety on this stretch known for ice and heavy traffic. Fence on outside of both separated lanes would not allow large or medium animals access to habitat remaining in median. This strip was considered useful for visuals only and effectively treated as non-habitat. Future issues will occur as a lack of herbivory and lack of fire in these vegetated medians continue to grow; currently the FS has no special management plan for this type of situation. Landscape architects assited in the design of visually benign fencing because the highway travels through the Newberry National Monument. The fence choice was black vinyl mesh (7.5‘ tall) with a smaller strip of fine mesh placed on bottom for small animals, in a lapped L shape.
The Lava Butte US 97 project was submitted for an award under the Greenroads program for these features as well as several others not discussed.
…Sandra Jacobson, July 20, 2010
Page Last Modified: October 27, 2011