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Three-Dimensional Visualization Aids Both Study and Recreation
Timpanogos Cave National Monument, Utah, Applies GIS
By B.E. McNeil, J.D. Jasper, D.A. Luchsinger, and M.V. Ransmeier
Timpanogos Cave (TICA) National Monument is a 250-acre site surrounded by forest service wilderness areas and easily accessible by more than one million people along the Wasatch Front, Utah. It is set in American Fork Canyon, a limestone canyon with geologically spectacular cliffs, avalanche chutes, pinnacles, and caves. The monument was created in 1922 to protect the Timpanogos Cave system, a set of three caverns perched in a cliff band 1,500 feet above the canyon floor. The cave system is known for its spectacular coloration and abundance of helictites. More than 70,000 visitors tour the caves each year and are placing increasing demands on the resources.
GIS has long been known as a valuable tool to better manage, interpret, and maintain resources. It is also a proven decision support system. With these benefits in mind, the managers at TICA sought to implement this valuable technology. Having worked closely over the years with Esri's Cave and Karst Program and also with Esri's Conservation Program, TICA chose to implement ArcView 3.2 with the ArcView Spatial Analyst and ArcView 3D Analyst extensions. TICA management then requested data development and GIS planning technical assistance from the National Park Service Intermountain Region GIS Support Office in Denver, Colorado. This request led to the development of a comprehensive GIS plan and the beginning of collaborations with the University of Denver Department of Geography. This last collaboration has been very fruitful; many of the data layers and applications presented in this report are the result of undergraduate and graduate research.
Data collection and development are paramount to applications in a GIS. Data development for a GIS must be customized to requirements and barriers of the study area. At TICA, all data must be high resolution, be highly accurate, and function relative to the extreme topography and/or three-dimensional cave environment. Data has been collected and developed from a variety of sources including GPS, hard-copy maps, existing information databases, and aerial photography. Many applications are made possible through the development of a high-resolution Digital Terrain Model (DTM). The DTM serves as the key base layer for TICA's GIS. This two-meter resolution DTM has been created through digitizing and interpolating 10-foot contour lines obtained from a hard-copy, 1 inch = 100 feet scale map. The terrain model has been checked for accuracy through the collection of 75 randomly distributed, highly accurate GPS control points. The accuracy and resolution of the DTM allows the GIS at TICA to visualize features and model phenomena in ways not possible with commonly available terrain models.
A demonstration of the power and usefulness of the DTM has come through the completion of a rockfall hazard model. The unstable Deseret Limestone geology, steep topography, and multitude of visitors all combine to make rockfall a hazard of much concern for managers at TICA. While rockfall chutes and many hazard-prone areas along the trail to the cave are well known, the GIS is now a powerful tool to quantify and objectify the rockfall hazard to TICA visitors, employees, and structures. The relative hazard model uses the DTM to delineate rockfall paths and determine slope while incorporating a vegetation map to account for friction. The velocity of falling rocks could be calculated for every location (grid cell) in a hazard area. Using this method, the rock's velocity is calculated at each cell using a mathematical equation accounting for friction, gravity, horizontal distance, and vertical distance of the rock's fall. As the equation was translated into an ArcInfo GRID modeling environment, the velocity was calculated through running the FLOWLENGTH GRID command over a cost-distance surface simulating resistance to rockfall. Because it was not possible or necessary to obtain exact rockfall velocities, the model results in output maps representing hazard in relative terms (e.g., low, high, and extreme), identifying dangerous rockfall paths. These maps are used by TICA management as planning and decision making tools for source area stabilization and hazard mitigation.
Visualizing and a Virtual Field Trip
The DTM and the GIS now allow management at TICA to visualize the cave and overlying terrain for purposes ranging from interpretation to natural resource management. Using the DTM and cave maps as background images, the park interpretive staff and the University of Denver have created a virtual field trip. While this field trip is structured and realized in a Web-based design, it is inherently a GIS application, interactively displaying and managing spatial information in the form of maps. The TICA virtual field trip is designed in a Web-based format to embrace the largest possible virtual visitor population and allow that population the freedom to explore the cave and cave trail from anywhere at any time.
The inspiration to create a virtual field trip for TICA arose largely out of the limited accessibility to the caves and the limited nature of interpretation along the trail leading to the caves' entrance. Because the Timpanogos Cave system is located high on the south wall of the American Fork Canyon, visitors must climb 1,065 feet in elevation over 1.5 miles of hard-surfaced trail to reach the entrance to the caves. This climb is challenging for most visitors and actually prevents a significant population from being able to reach the caves at all. During the late fall and winter months, the trail is completely closed to the public because of dangerous ice and snow on the trail as well as increased rockfall hazard. Virtual field trips enable people to experience the full resources of TICA regardless of their physical condition or the time of year. It is hoped that TICA will soon be able to provide access to the virtual field trip from its visitor center so that during times of inclement weather or when visitors find themselves unable to hike the trail, they will be able to enjoy the park.
Visitors to TICA's virtual field trip may choose to "hike the trail" or "tour the cave" from the home page (www.nps.gov/tica/index.htm).
Visualizing and Natural Resource Management
Natural resource management has also benefited greatly from the visualization opportunities of the GIS at TICA. One of the most basic gains in understanding the cave resource has come through visualizing the cave and its overlying topography. The three-dimensional cave line plot is created through reading the survey coordinates (distance, bearing, and altitude) into COMPASS software (www.fountainware.com/compass). The CAVETOOLS extension of ArcView will then convert the COMPASS data to a three-dimensional ArcView shapefile. GPS locations of surface features identifiable on the original cave survey are used to georeference the three-dimensional shapefile.
Creating GIS layers of cave features is problematic since aerial photography and GPS techniques are not possible. To overcome these obstacles, a scanned Timpanogos Cave map was georeferenced to the line plot shapefile. This map provides an excellent base for recording and planning management actions. The cave map is the ultimate utility for management of cave-related data. Currently the park is documenting its cave cleaning efforts, photomonitoring points, habitat zones, electrical corridors, place names, and significant cave features. GIS provides the framework for managing all this data in its natural, spatially interconnected environment. Powerful resource management decisions and conclusions are now available because of this more spatially aware information management.
A longer version of this article appeared in the Journal of Cave and Karst Studies (April 2002, Vol. 64, No. 1). To read the complete article with references, visit www.caves.org/pub/journal/PDF/V64/v64n1-McNeil.pdf. For more information, contact Brenden McNeil (e-mail: email@example.com).
To learn more about GIS for Cave and Karst, see www.esri.com/cave.