Report Number: 126
Year: 2010

Spatial Distribution of Badlands in the Ugum Watershed: Characterization and Temporal Analysis

Soil erosion, rather common in the southern part of Guam, marks the savanna landscape in the form of erosion scars. These large, orange-red colored patches are often called badlands. Soil erosion not only degrades the quality of the topsoil, but also severely impacts the water quality in the streams and the ocean where it also affects the coral reef system and marine flora and fauna. Several studies (Khosrowpanah et al. 2007, Golabi et al. 2005, Scheman et al. 2002, Lewis 1999) have shown that badlands are one of the major contributors of soil erosion and associated sedimentation. Although several studies have measured erosion rates of badlands on Guam, the change of badlands through time as well as terrain attributes (that affect badland distribution) was unknown prior to our study. We utilized a geographic information system (GIS) to quantify temporal changes in badland coverage of a historical aerial image and up-to-date satellite imagery in our study area in the Ugum Watershed. In addition, we conducted a quantitative spatial analysis of badlands and their distribution to characterize badlands in respect to terrain attributes like elevation, slope, slope direction (aspect), distance to drainage divide, geology, and soils. Our results show that badlands have expanded over time, but they also have the ability to recover. More studies on badland change over time in other areas on Guam at a smaller time-interval are needed to more accurately determine the overall rate of badland change. We also found a significant relationship between proportional abundance of badlands and elevation, slope, distance to drainage divide, and soils. The relationships of the spatial distribution of badlands and terrain attributes provide the basis for future development of a predictive model for mapping potential badland areas on southern Guam.

Shahram Khosrowpanah
Yuming Wen
Maria Kottermair