In Mediterranean semi‐arid conditions, the availability of studies monitoring channel adjustments as a response to reforestation and check dams over representative observation periods, could help develop new management strategies. This investigation is an integrated approach assessing the adjustments of channel morphology in a typical torrent of southern Italy after land‐use changes and check dam construction across a period of about 60 years. A statistical analysis of historical rainfall records, an analysis of land‐use changes in the catchment area and a geomorphological mapping of channel adjustments were carried out and combined with field surveys of bed surface grain‐size over a 5‐km reach including 14 check dams. The analysis of the historical rainfall records showed a slight decrease in the amount and erosivity of precipitation. Mapping of land‐use changes highlighted a general increase of vegetal coverage on the slopes adjacent to the monitored reaches. Together with the check dam network installation, this increase could have induced a reduction in water and sediment supply. The different erosional and depositional forms and adjustments showed a general narrowing between consecutive check dams together with local modifications detected upstream (bed aggradation and cross‐section expansion together with low‐flow realignments) and downstream (local incision) of the installed check dams. Changes in the torrent bends were also detected as a response to erosional and depositional processes with different intensities. The study highlighted: the efficiency of check dams against the disrupting power of intense floods by stabilizing the active channel and the influence of reforestation in increasing hillslope protection from erosion and disconnectivity of water and sediment flows towards the active channel. Only slight management interventions (for instance, the conversion of the existing check dams into open structures) are suggested, in order to mobilize the residual sediment avoiding further generalized incision of the active channel and coast line erosion. Copyright © 2017 John Wiley & Sons, Ltd.

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The effectiveness of check dams on channel morphology of managed torrents is rarely assessed. Therefore, there is a need for studies that focus on the impacts of existing engineering check dams on the planoaltimetric characteristics of the torrent, particularly in Mediterranean areas, where the hydrological regime of ephemeral channels is dynamically unsteady. The quantitative evaluation of the effects of the check dams on channel morphology after many years (i.e., at least four or five decades) helps introduce innovations to the usual analysis of check dam efficacy which have often been limited to qualitative observations for only a few years after installation. As a contribution to make up these shortcomings, this paper investigates the geomorphologic asset of a torrent in southern Italy containing 10 check dams (installed in the 1950s to 1960s) and analyzes the dynamics of the scouring and sedimentation processes upstream and downstream of selected check dams after 8 rainfall events; moreover, the capability of the model by Castillo (2007) to predict scouring/ sedimentation in proximity to these check dams is assessed. Sediment stored upstream of each check dam (where lower channel gradients and wider channel sections formed very long and wide sedimentary wedges) is more than one order of magnitude higher compared to scouring downstream. The morphological analysis revealed that the check dams installed in the headwater reach play a function of bed stabilization (due to the longitudinal slope reduction) and flood lamination (because of the wider channel section) rather than a role of sediment collectors as their sediment storage capacity has already been completed. Scouring/ sedimentation dynamics depend mainly on the channel slope and width in proximity to the check dams rather than on structure height. Finally, Castillo's model showed an acceptable performance in predicting scouring/sedimentation in the channel bed close to check dams after the monitored rainfall events, the model efficiency being satisfactory and the differences between the mean observed and simulated values low. This investigation improves the understanding about morphological effects of check dams in Mediterranean torrents based on field observations and quantitative analysis.

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