A B S T R A C T This study demonstrates a human impact on the development of active drainage network (ADN) operating during heavy rainfall in a medium-high relief flysch catchment. The ADN was reconstructed with the use of ALS-LiDAR data. The results have revealed that the density of the ADN (11.2 km•km −2 ) is c.a. 5 times higher compared to the river system (2.2 km•km −2 ) and c.a. 25% of the ADN constitutes man-origin elements (roads, ditches and plough furrows), which are incorporated into

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... he drainage system. The Hortonian's type of analysis has revealed that man-origin elements significantly change the structure of a natural, river drainage system, and man-origin elements are predominantly attributed to 1st and 2nd order streams, which drain the upper part of the hillslopes. Roughly up to 37% of 1st and 2nd order streams are the man-origin elements of the ADN and those streams drain c.a. 22% of the catchment area. Quantification of the changes in the ADN gave the opportunity to analyze the hydrological response of a catchment. The results have revealed that the reconstruction of flood wave parameters by rainfall-runoff (SCS-CN and GIUH models) hydrological models is more accurate when the Horton's parameters describe ADN operating during heavy rainfall. It has been revealed that alteration of the ADN influences the flood wave peak predominantly, increasing it up to 11%.