Structural control on drainage network orientation -an example from the Loucka drainage basin, SE margin of the Bohemian Massif (S Moravia, Czech Rep.)  

This paper discusses the relationship between geological structure and drainage network orientation at both a meso-scale and local scale. The Loucka Basin, located at the SE margin of the Bohemian Massif (S Moravia, Czech Rep.), has been selected as the model region for these studies. In the Loucka Basin, the bedrock comprises the metamorphic rocks of the Moldanubicum Group, which are arranged in elongated bands and lenses and are fractured with the dense network of faults. There is no extensive cover of unconsolidated younger sediments in the basin, nor any deep weathering regolith. In these respects, the geological setting is extremely favourable for the quantification of structural features and their correlation with drainage orientation. The degree of correspondence between the direction of drainage network segments and the orientation of such structural features as faults, mylonite zones, thrust-fronts and rock lineations was investigated in five study areas. The third-order streams are those most influenced by structure. The higher the order of stream segment, the weaker the correlation, and the more important the overall inclination of the terrain as a controlling factor in stream flow orientation. However, there is a strong structural control of first order streams in the periphery of the Basin. The structural control of streamflow direction in the Loucka Basin, which is built up with Precambrian metamorphic rocks, varies between 30-50% of the rectified channel length; the upper limit is considered to be the maximum conditioned by a local very high density of various linear structural elements.