THE ALLEN RESIDENCE, A MOUNTAIN DREAM HOME
by Richard Giraud
Investigation into a residence destroyed by avalanches provides an excellent example of poor avalanche hazard land-use planning. The Allen residence was a mountain dream home constructed in an avalanche runout zone near the Sundance Ski Resort, Utah. A chronology of events pertaining to the Allen residence was used to investigate residential development of an avalanche runout zone and the resulting economic loss. Structural damage and economic loss could have been prevented if adequate land-use planning and engineering guidelines were followed.
On February 13, 1986, the residence was struck by an avalanche which substantially damaged the structure. A law suit, Transamerica Insurance Company v. Sundance Development Corporation and others was filed and eventually dismissed without a conclusive ruling. On February 25, 1993, the residence was struck by a second avalanche destroying the remaining structure and damaging adjacent homes. Mapping of vegetation patterns and avalanche terrain could have provided design information for avalanche magnitude, frequency and runout behavior. Mitigation of the avalanche hazard is critical to avoid additional damage to adjacent homes and possible loss of life. Hazard mitigation could include both operational and structural methods.
The Allen residence was a private home that was struck by two snow avalanches. This paper presents a chronology of events regarding the Allen residence, avalanche hazard evaluation techniques to define the hazard and mitigation possibilities for remaining homes exposed to the avalanche hazard. The Allen residence is located in the Wasatch Mountain Range ten miles east of Orem, Utah. The Allen residence is part of the Sundance Mountain Home Development which is northwest of the Sundance Ski Resort.
Two other homes are located adjacent to the Allen home, one uphill and one downhill. The homes are located in the runout of the Bearclaw (sic) avalanche path. Several avalanche paths are present west and southwest of the site. U. S. Forest Service land is present west of the site and is part of the Mt. Timpanogos Wilderness Area. The homes have a spectacular view of Cascade Cirque and the Stewarts Cascades (waterfalls) on the east side of Mt. Timpanogos. The view includes nearly 5,000 vertical feet of relief.
When the residence was struck by the first avalanche it was owned by Robert Allen. For the purposes of this paper the residence or destroyed residence is referred to as the Allen residence. Locally the site is known as the Allen house.
Several sources were utilized to construct the chronology of the Allen residence. Utah County planning files provided information on the building permit, plat maps of the development, and the protective covenant for the development. Utah County assessor records were used to document the property value through time. U. S. District Court records were useful in obtaining a consulting report of the 1986 avalanche damage and court decisions. The Daily Herald was used to gain newspaper information concerning avalanche dates and damage. Utah Avalanche Forecast Center (UAFC) avalanche advisories are used to profile the forecasted backcountry avalanche hazard.
Field visits were used to observe terrain, avalanche path aspect, age density and types of vegetation, vegetative growth patterns, and character of damaged vegetation. Slope angles used in this report were measured on profiles constructed from the U. S. Geological Survey 7.5 minute Aspen Grove quadrangle and directly from slopes in the field.
HISTORICAL BACKGROUND AND PREVIOUS WORK
Snow avalanches have always conflicted with human development in the Wasatch Mountains. Historical usage of the Wasatch Mountains has shifted from mining to winter recreation and development. Likewise, the avalanche hazard has shifted from mining to winter recreation and development.
In describing avalanches along the Wasatch Front, Perla (1971) points out that a growth in winter usage and development has increased public exposure to avalanche hazard. Perla provides examples of evaluating sites based on terrain and vegetation when planning new construction. Perla also lists avalanches that have caused property damage in Provo Canyon.
Christian (1986), in a Daily Herald newspaper article describes avalanches at Bridal Veil Falls in Provo Canyon. Large avalanches occurred at Bridal Veil Falls during March 1924, February 1932 and February 1986. Bridal Veil Falls is approximately three miles south of the development.
DESCRIPTION OF DAMAGING AVALANCHES
February 13, 1986 Avalanche
The avalanche path is an uncontrolled hazard and representative of backcountry avalanche conditions. The backcountry avalanche forecast issued by the UAFC is used to profile the avalanche hazard at the time of the slide. The UAFC issued an avalanche warning on the morning of February 13, 1986 for the northern Wasatch Mountains from the Utah-Idaho border to Spanish Fork Canyon, which includes the Provo area mountains (UAFC, 1986). Fourteen to thirty three inches of high density new snow was reported throughout the mountains. The backcountry avalanche hazard was reported as extreme with large destructive avalanches certain. The forecast advised staying well away from large avalanche runout zones. The avalanche warning remained in effect through February 22, 1986.
February 25, 1993 Avalanche
The UAFC backcountry avalanche forecast for February 25, 1993 was for a high hazard at upper elevations exposed to wind and that natural avalanches were occurring on slopes of all aspects 35 degrees and steeper (UAFC, 1993). Later in the day on February 25, 1993 after more snow had fallen, the hazard was forecasted as high on slopes 30 degrees and steeper and elevations above 6,500 feet.
Both avalanches were part of major avalanches cycles affecting the Wasatch Mountains. The February, 1986 cycle was a longer cycle, however, both cycles caused significant property damage and loss of human life in the Wasatch Mountains.
UTAH COUNTY PLANNING AND ASSESSOR RECORDS
U. S. DISTRICT COURT RECORDS
A law suit resulted from the February 13, 1986 avalanche. The suit was filed in the U. S. District Court, District of Utah, Central Division in Salt Lake City. The case, Transamerica Insurance Company v. Sundance Development Corporation and others was filed in 1987 (Case No. 87C-0921S). A court order on November 8, 1989 dismissed the case and stated that each party bear its own costs.
ALLEN RESIDENCE SUMMARY CHRONOLOGY
The following is a summarized chronology of the Allen residence.
-September 2, 1983 the building permit is approved.
-The accessed 1985 market value of the property is $836,369.
-February 13, 1986 the home is struck by an avalanche. No one was in the home at the time of the slide. Damage was extensive.
-Accessed 1986 market value of the property after the February 13, 1986 avalanche is $582,882.
GEOMORPHOLOGY AND VEGETATION MAPPING
The Bearclaw Cabin avalanche path is a steep northeast facing gully directly above and southwest of the Sundance Mountain Home development. The Allen residence is adjacent to steep mountainous terrain on a north facing slope at an approximate elevation of 6,700 feet. The avalanches travel approximately 1,900 feet vertica1 and 3,300 feet horizontal to reach the Allen residence. The slope angles of the avalanche starting zone and track are 37 degrees. Avalanche flow is confined in the starting zone and track by a gully. Avalanche flow is unconfined in the runout zone. The runout slope angle in the vicinity of the Allen residence is 17 degrees. Historical avalanche behavior has demonstrated that the runout slope angle is too steep for moderate and large avalanches to decelerate and stop before impacting the Allen residence.
Surrounding mountain slopes have forests of conifer and aspen trees. Scattered conifers, aspen and small shrubs are present near the Allen residence. Mature conifer trees are present outside of active avalanche paths. Burrows and Burrows (1976), mention that shrubs are often useful indicators of the frequency of avalanching or intensity of disturbance because they can grow in sites where trees cannot survive. Frequent avalanching keeps the vegetation in the starting zone and track to a minimum. Frequent avalanching also has resulted in small trees and shrubs in the runout zone.
The vegetation trim lines in the avalanche runout are both sharp and ragged. The trim lines suggest different avalanche flow patterns in the runout. Many of the conifer trees near the Allen residence and adjacent homes are missing the uphill branches. The apparently avalanche damaged conifer trees and shrubs near the homes suggests that avalanches runout into the developed home area.
AVALANCHE HAZARD PLANNING, EXISTING HAZARD AND MITIGATION
Avalanche Hazard Planning
tool to avoid areas where the risk is unacceptable and to properly design structures to reduce the risk presented by avalanches.
A study of the avalanche hazard would have provided planning and development guidance. The hazard and associated risks could be quantified objectively. The frequency and magnitude of avalanches impacting the site could have been estimated. Avalanche runout distances, velocity and impact pressure could be estimated and used in the design and location of homes.
Existing Avalanche Hazard
Avalanche Hazard Mitigation
Even though the mitigation possibilities are limited because the homes are constructed, structural and operational mitigation methods should be evaluated. Structural mitigation methods could involve the construction of arresting, deflecting or catchment structures in the runout zone. Supporting structures in the starting zone would not be possible because the starting zone is in the Mt. Timpanogos Wilderness Area where permanent manmade structures are not allowed.
Operational mitigation methods could consist of seasonal occupation, occupation with an evacuation alternative and explosive control of avalanches. Seasonal occupation would involve usage when the avalanche hazard is not present, generally May through October. Occupation with an evacuation alternative could be used to reside in the homes during the winter months. Evacuation would be based on avalanche hazard forecasting. Seasonal occupation and occupation with an evacuation alternative only protects human life and not damage to structures. Artificial release of avalanches by explosives is a widely used form of mitigation for ski areas and highways. Artificial release generally involves the release of smaller avalanches to limit the release of large avalanches.
Snow avalanches have conflicted with human habitation in the Wasatch Mountains since the area was first settled in the mining era of the late 1800's. The Allen residence was constructed in an avalanche runout zone and was destroyed by avalanches. The adjacent homes remain exposed to the hazard. The property damage and economic loss may have been avoided if adequate land use planning would have been followed. A study of the hazard could have provided planning and development guidance.
Based on recent history and vegetation patterns, avalanches will continue to impact the homes adjacent to the Allen residence. The Allen house and adjacent homes were constructed without any regard to the avalanche hazard. Mitigation possibilities are limited because of this. Different mitigation methods should be evaluated to determine hazard reduction, mitigation effectiveness and cost feasibility.
Avalanches are a normal process of nature. Nature cannot be fooled and the future will always come. Avalanches will continue to run into the developed home area. If the hazard is not mitigated, additional property damage will result and human lives may be lost. As the philosopher George Santayana said: "Those who fail to remember the past are condemned to repeat it".
I would like to thank Rand Decker for his suggestion of the problem, his discussion and use of photographs. Bruce Tremper was very helpful in supplying avalanche forecast and weather data. Darce Trotter was helpful to focus the project.
Burrows C. J., and Burrows V. L., 1976, Procedures for the study of snow avalanche chronology using growth layers of woody plants: Institute of Arctic and Alpine Research, University of Colorado, Occasional Paper No. 23, 54 p.
Henetz, P., 1993, Avalanche kills skier, icy roads closed in Wasatch canyons: The Daily Herald, Provo newspaper article Saturday February 26th, l l9th year, p. A3.
Karren and Associates, 1986, Robert G. Allen Residence - final report: Unpublished consulting engineering report on avalanche damage to the residence, 6 p.
Keaton, J. R., 1988, A probabilistic model for hazards related to sedimentation processes on alluvial fans in Davis County Utah: Unpublished PhD Dissertation, Texas A&M University, 441 p.
Mears, A. I., 1993, Snow-avalanche hazard analysis and mitigation methods on highways: Transportation Facilities through Difficult Terrain, Wu and Barrett editors,Balkema, Rotterdam, p. 487-494.
Mears, A. I., 1989, Avalanche runout distances and dynamics - current methods and limitations: The Avalanche Review, Vol. 7, No. 4.
Perla, R. I., 1972, Snow avalanches of the Wasatch Front: Environmental Geology of the Wasatch Front, Utah Geological Association Publication 1-O, 25 p.
U. S. Forest Service, 1993, February 1993: Avalanche Notes, U. S. Forest Service Westwide Avalanche Network, Fort Collins, Colorado, unpublished monthly report.
U. S. Forest Service, 1986, February 1986 revisited: Avalanche Notes, U. S. Forest Service Westwide Avalanche Network, Fort Collins, Colorado, unpublished monthly report.
Utah Avalanche Forecast Center, 1993, Backcountry avalanche and mountain weather advisories February 13 through February 27, 1993: Utah Avalanche Forecast Center, U.S.D.A. Forest Service Wasatch-Cache National Forest and N.O.A.A. National Weather Service, unpublished public avalanche advisories.