Assessing the long-term effectiveness of channel control works and supporting watershed management through sediment dynamics studies

In risk management of mountain basins, quite often, there is a lack of information on the efficiency of existing structures, the evolution of the ongoing process, and a priori in-depth study to analyse the sediment morphology dynamics and the interaction with existing channel control works. The growing capability of producing High-Resolution Topography data (HRT) greatly simplifies the analysis of geomorphological changes at multiple spatial and temporal scales and enables the development of innovative approaches to monitor sediment morphology dynamics and understand the interaction with channel control works. Indeed, thanks to multi-temporal HRT surveys (e.g., Airborne Laser Scanning - ALS), it is possible to derive accurate multi-temporal Digital Terrain Models (DTMs), and reliable DTMs of Difference (DoDs) useful to quantify the morphological changes also in catchment areas covered by vegetation. However, without a methodological and detailed workflow that considers the differences in terms of accuracy between old “legacy” data sets and recent surveys and the errors associated with the processes of co-registration, it would not have been possible to obtain accurate and valid multi-temporal DoD. The information provided by sediment morphology dynamics (i.e., exploiting multi-temporal DoDs at catchment and reach scale) coupled with a very simple, quick, and user-friendly efficiency index of channel control works, could help to support the development of watershed management strategies, assess afterward the effectiveness of existing structures, and foster a more complete decision-making chain. Therefore, this research aims to introduce a methodological approach based on integrating the sediment morphology dynamics data over large time spans in some mountain catchments with an updated state of efficiency of existing interventions. Various examples of the proposed methodology emphasized the usefulness of providing more complete information, than in the past, by exploiting field surveys and remote sensing data, in a context such as the risk management process where uncertainty and incomplete information on the ongoing phenomena prevails. The realized database could be a starting point for further analysis or provide numerical data for prediction models of the life-cycle of channel control works in risk management processes. Finally, the methodological workflow proposed could provide increasingly up-to-date information to constantly identify the areas most prone to hazards, support effective risk management decisions, improve intervention planning, find more appropriate solutions, or direct the maintenance works.