Valley Network Evolution in Sandstone Terrains: Tectonic Controls and Surface–Subsurface Process Interactions Revealed by Geomorphometric Analyses and Field Surveys

Valley networks in sandstone terrains are commonly interpreted as products of structurally-controlled fluvial incision, coupled with hillslope and denudational processes. However, the role of tectonic and subsurface controls in shaping valley morphology and drainage organisation remains insufficiently explored. This study addresses the interplay between surface and subsurface processes in a sandstone tableland, with particular emphasis on tectonic controls, lithological variability, and their influence on valley network geometry and morphological diversity of valleys.

The sandstone-dominated area of the Intra-Sudetic Trough (NE Bohemian Massif) was examined using geomorphometric methods applied to high-resolution airborne LiDAR-derived digital elevation models. A set of primary and secondary topographic indices was calculated to characterize drainage organisation, valley incision, and spatial patterns of erosional dissection. These indices were subsequently integrated using two types of cluster analysis to delineate areas with an enhanced erosional signal.

To complement the geomorphometric analysis, field investigations were conducted, including detailed landform mapping and geophysical surveys employing Electrical Resistivity Tomography (ERT). These data, supplemented by analyses of sandstone composition and petrographic characteristics, provided insights into the links between surface, near-surface, and subsurface processes and geological controls, enabling for the development of a conceptual framework for valley network evolution.

The results demonstrate that valley morphology in sandstone terrains reflects a complex interaction between tectonic structures, lithology, and surface–subsurface process coupling. Pre-existing fault systems and joint networks exert a strong influence on drainage orientation, valley spacing, and incision patterns, often preconditioning zones of enhanced erosion. These structural controls, combined with differential weathering and subsurface erosion, promote the development of a wide spectrum of valley forms, including narrow canyons, gorges, V-shaped valleys, broad troughs, and flat-bottomed valleys, occurring in varied morphological positions within the sandstone-dominated landscape.

The observed morphological diversity cannot be explained solely by rock control on surface fluvial processes. Instead, the study highlights the importance of subsurface processes such as dilation-driven rock mass disintegration, chemical weathering, and fracture-guided underground erosion. The integration of geomorphometric techniques with field-based and geophysical data provides a quantitative and process-oriented perspective on valley network evolution.