USING TERRESTRIAL LASER SCANNING FOR MODELING HYDROLOGY: A CASE STUDY ON OFU ISLAND, AMERICAN SAMOA

Terrestrial Laser Scanning (TLS) is becoming an increasingly used technology in many fields of geology. In geoarchaeology, most applications for TLS focus on measuring rates of change or cultural preservation. In this project, we apply TLS to develop high resolution DEMs to model the hydrology of prehistoric ditches not visible on one-meter DEMs derived from aerial lidar. Our case study for this application is on Ofu Island in the U.S. Territory of American Samoa, in the south-central Pacific. Because Ofu is a steep volcanic island in the tropics, our methods address many of the common challenges associated with using TLS in heavily vegetated regions. In addition, our understanding of the unique anthropogenic landscape of the island interior is enhanced by the acquisition of the high resolution TLS data. These data, paired with hydrologic modeling, provide a unique analytical approach to understanding the purpose of ditch networks created by late prehistoric Samoans. Initial results suggest that the high slope of most of these ditches would allow for a large flow capacity, likely surpassing the flow generated during a typical storm event. Furthermore, because the ditches are so large, they are unlikely to have served as solely a social function such as land boundaries and status markers, although they may have served both environmental and societal functions, simultaneously.