VISUALIZING THE RELATIONSHIP BETWEEN THE BEDROCK AND SURFACE TOPOGRAPHY OF THE ROCK RIVER VALLEY NEAR THE QUAD CITIES, IL WITH ArcGIS

This study evaluates the relationship between the bedrock and surface topography of the Rock River Valley near the Illinois Quad Cities. The study area is within the Milan and Coal Valley, IL, Quadrangles along the north and south sides of the Rock River. A high resolution 10 ft (3.05 m) contour interval bedrock topographic map will be constructed, from data obtained from water well logs from the Illinois Water Well (ILWATER) Internet Map Service as well as from bedrock outcrops in the study area. Data for the surface topography was obtained from a high-resolution DEM of Rock Island County that was constructed from LIDAR data. These data were compiled into a database and was visualized using ArcGIS software. ArcScene was used to create a 3D visualization of the surface topography and the bedrock topography. The Rock River flows west through a broad but shallow valley that extends southwest from the Green River Lowland, a very deep bedrock valley. Bedrock elevations increase further from the Rock River into the upland bluffs along the north and south sides with a relief of 15 to 30 m. There is a subtle conformity between the surface topography and the bedrock while the relief of the bedrock is not as steep as the relief of the bluffs. The bedrock surface within the study area is mainly Pennsylvanian shale and Devonian limestone, overlain by up to 30 m of glacial drift (till, outwash, glaciolacustrine deposits, and loess) as well as modern alluvium. Understanding the relationship between the bedrock topography and the surface topography is important for construction, exploitation of natural resources, as well as for understanding the local aquifer systems and the origin of the modern landscape.