ABSTRACT We examine the sensitivity of 10Be concentrations (and derived denudation rates), to debris‐flow and anthropogenic perturbations in steep settings of the Eastern Alps, and explore possible relations with structural geomorphic connectivity. Using cosmogenic 10Be as a tracer for functional geomorphic connectivity, we conduct sampling replications across four seasons in Gadria, Strimm and Allitz Creek. Sampling sites encompass a range of structural connectivity configurations, including the conditioning of a sackung, all assessed through a geomorphometric index (IC). By combining information on contemporary depth of erosion and sediment yield, disturbance history and post‐LGM (Last Glacial Maximum) sedimentation rates, we constrain the effects of debris‐flow disturbance on 10Be concentrations at the Gadria sites. Here, we argue that bedrock weakening imparted by the sackung promotes high depth of erosion. Consequently, debris flows recruit sediment beyond the critical depth of spallogenic production (e.g., >3 m), which in turn, episodically, due to predominantly muogenic production pathways, lowers 10Be concentration by a factor of 4, for at least 2 years. In contrast, steady erosion in Strimm Creek yields very stable 10Be concentrations through time. In Allitz Creek, we observe two‐ to fourfold seasonal fluctuations in 10Be concentrations, which we explain as the combined effects of water diversion and hydraulic structures on sediment mixing. We further show that 10Be concentration correlates inversely with the IC index, where sub‐basins characterized by high concentrations (long residence times) exhibit low IC values (structurally disconnected) and vice versa, implying that, over millennial time scales a direct relation exists between functional and structural connectivity, and that the IC index performed as a suitable metric for structural connectivity. The index performs comparably better than other metrics (i.e., mean slope and mean normalized channel steepness index) previously used to assess topographic controls on denudation rates in active unglaciated ranges. In terms of landscape evolution, we argue that the sackung, by favouring intense debris‐flow activity across the Holocene, has aided rapid postglacial reshaping of the Gadria basin, which currently exhibits a topographic signature characteristic of unglaciated debris‐flow systems. © 2020 John Wiley & Sons, Ltd. Bedrock weakening within sackung perimeter promotes debris‐flow erosion beyond critical depth for spallogenic production, which perturbs 10Be downstream. Debris‐flow occurrence along colluvial channels lowers 10Be (and elevates corresponding apparent denudation rates) by a factor of four, for over 2 years. Functional geomorphic connectivity, evaluated through 10Be, displays high direct correlation with geomorphic structural connectivity (i.e., IC index) over 102 to 103‐year timescales. Water diversion and hydraulic structures, by altering sediment mixing, induce two‐ to fourfold seasonal fluctuations in 10Be.