Tuesday, November 14, 2006

Merging Digital Soil Surveys and Landscape Models: Application to Mapping Surficial Geology.

Michael Barnhardt and Donald Luman. IL State Geological Survey, 615 E Peabody Dr, Champaign, IL 61820

Early in their respective projects, a geologist, mapping the surficial geology, and a soil scientist, developing a soil survey, may share a similar goal: creating a conceptual model that depicts the character of geologic sediments (parent materials) on the landscape. This sediment-landscape assemblage is actually a thin, three-dimensional model because pedologic information may be collected to depths of 10 ft, and geologic information to 50 ft or more below land surface. Although the broader objectives of these two projects may differ, they share the need to interpret accurately the relationship between landscape position and parent material, and identify any patterns. Increasingly, digital soil surveys and high resolution digital terrain models are available for areas where detailed geologic mapping (1:24,000-scale) is planned. Within a GIS, we produced a soil-landscape model by draping geologic and parent material data and high resolution color orthophotography over a LiDAR-derived digital elevation model with a one-foot vertical resolution. This model served as a framework to plan our fieldwork, which involved extensive drilling to depths of 50 ft or more. The model is especially useful when mapping near wetlands and other transitional areas. We used a digital 1939 orthophotograph with a wetlands coverage to map changes at a specific site. Models have been developed for a variety of landscapes including 1) low-relief floodplains, 2) high-relief terrains with complex landscape components, and 3) low-relief uplands with minimal drainage development. The utility of the model is related to the complexity of the landscape and near-surface geology but it provides a first look at the surficial geology mapping units. Information derived from the model is used by municipalities and county agencies for land use planning, aquifer protection, and other environmentally-related issues.