PRELIMINARY LANDSLIDE INVENTORY & SUSCEPTIBILITY MAPPING OF DRIFT CREEK WATERSHED, OREGON, USING LIDAR DATA

Landslides are one of the most significant natural hazards in Oregon, resulting in millions of dollars worth of damage annually. Recognition of landslides and their susceptibility in problematic areas enables communities to reduce risk and ensure safe living conditions. The goal of this study is to create a landslide inventory map for the Drift Creek watershed in the Oregon Coastal Range, using the protocol established by the Oregon Department of Geology and Mineral Industry (DOGAMI) as outlined in Burns and Madin (2009). In addition, shallow and deep landslide susceptibility maps are to be created in order to identify vulnerable areas to future landsliding.

The Driftcreek watershed is of particular importance because it presents various land management practices, some of which influence mass wasting. Excessive sedimentation, turbid waters, and stream warming within this watershed are of concern to the Oregon Department of Environmental Quality (DEQ). This project will aid future work and development within this area as well as surrounding watersheds, which experience similar water quality issues.

Landslides have been located and formatted through applications of a geographic information system (ArcGIS). Digital elevation models (DEMs) are derived through light detection and ranging (LiDAR) data, which allow visualization of the bare earth. Landslide deposits, scarp flanks, and scarps are outlined using LiDAR-derived DEMs such as hillshades, slope maps, and topographic contours, which highlight geomorphologic features. Other images such as orthophotography, geological maps, and previous landslide inventories, were used to understand the historical and present uses of land. Attributed data for every landslide is discerned based on these practices.

Certain landslides have been field checked in order to guarantee the confidence of spatial and tabular data. Rock and soil samples were taken in order to evaluate geotechnical properties found in this area. Parameters are than utilized in the susceptibility maps, which are created using the infinite slope analysis.

This data can be translated into meaningful results, which can determine how much sediment is reaching river systems, the erodible nature of the landscape, influence of human activities on landsliding, land-use planning, and much more.