The roughness of fracture surfaces and its scale dependence – a methodological study based on natural fractures in sandstones from Southern Germany

The study of groundwater flow in fractured aquifers is an important part of hydrogeology. Main parameters that influence the flow rate and velocity in fractures are their number and connectivity but especially their opening width (aperture). The roughness of fractures also has an important influence, as it locally modifies both aperture and flow patterns. However, it is seldom measured, not fully understood and, therefore, often not included into calculations. The present study focuses on methodological aspects and investigates the roughness and composition of weathered fracture surfaces from Triassic Bunter Sandstone samples from Southern Germany. Such weathered surfaces have received little attention so far. For the first time, different mechanical and optical methods were used and compared. Results show a clear scale dependency, indicating a fractal, self-affine nature, despite several different methods being used. This confirms that all methods provide useful data. .