ASSESSING AND DISPLAYING LANDSLIDE HAZARDS, BADLANDS NATIONAL PARK, SOUTH DAKOTA

The goal of this study is to assess and communicate hazards associated with landslides in the Badlands National Park using geological mapping and innovative GIS data gathering and display techniques. The current geological map of the Badlands National Park (1:62,500 scale) was published in 1976. While an excellent map, it gives little information useful for hazard assessment other than distribution of slide deposits. The goal here is to create a detailed map of slide distribution together with information on slide mechanisms, timing, and bedrock geologic factors that contribute to hazards. These data are displayed in GIS formats that are interactive, can be quickly updated, and useful for analysis.

Landslide zones in the Badlands are especially hazardous to park infrastructure; the main road through the park crosses three of the largest slide zones. At these crossings, road stabilization has been ongoing and expensive. Creep rates of 50 to 125 mm/week were recorded by geotechnical investigators at Cedar Pass prior to stabilization efforts in 2000. In addition to creep, there is significant danger of catastrophic slumping and rock toppling in these zones. Geologic conditions that contribute to slide formation include loosely consolidated strata, precipitation events, the presence of swelling clays, vertical jointing, and a structural dip towards the river valley.

In addition to assessing hazards, we are attempting to use GIS techniques in innovative ways. In this first phase of the project, using data gathered in three field seasons, we created a digital base map of the project area in ESRI’s ArcGIS Software. Point, line and polygon vector data were gathered with the use of both sub-meter Trimble GeoXT and Garmin GPS units. Together with field notes, drawings and hyperlinked digital images at specific landslide locations, data was checked into the project Geodatabase and specific feature classes were created/updated and overlaid on high-resolution imagery. Analysis was then performed on the layers to create distinct spatial and temporal boundaries based on geologic beds and historic activity. This state of the art geospatial digital map allows the map user greater access to spatial/geologic information and interpretation of the field area than a traditional geologic map.