Artificial water storage, originated by the construction of dams, is essential for the sustainable health and welfare of civilizations since it supplies water for human consumption, irrigation and energy production. Furthermore, dam reservoirs are used for recreation, navigation and they provide safety in the downstream valleys against extreme flood events and droughts. All reservoirs are subjected to sedimentation which, without adequate prevention and mitigation counter-measures, threatens their sustainability. As well as the evident loss of storage capacity, the adequate and safe operation of water intakes and bottom outlets belonging to the vital outlet structures can be affected by the deposition of sediments in the reservoir. This Vision Paper first addresses the state-of-the-art and the main scientific advances in terms of prevention and mitigation measures against sedimentation in reservoirs. Then, the main research challenges, which result from the assessment of what are the remaining open questions, are pointed out. The emerging research methodologies to study sedimentation processes are also discussed.

Soil and water bioengineering is a technology that encourages scientists and practitioners to combine their knowledge and skills in the management of ecosystems with a common goal to maximize benefits to both man and the natural environment. It involves techniques that use plants as living building materials, for: (i) natural hazard control (e.g., soil erosion, torrential floods and landslides) and (ii) ecological restoration or nature-based re-introduction of species on degraded lands, river embankments, and disturbed environments. For a bioengineering project to be successful, engineers are required to highlight all the potential benefits and ecosystem services by documenting the technical, ecological, economic and social values. The novel approaches used by bioengineers raise questions for researchers and necessitate innovation from practitioners to design bioengineering concepts and techniques. Our objective in this paper, therefore, is to highlight the practice and research needs in soil and water bioengineering for reconciling natural hazard control and ecological restoration. Firstly, we review the definition and development of bioengineering technology, while stressing issues concerning the design, implementation, and monitoring of bioengineering actions. Secondly, we highlight the need to reconcile natural hazard control and ecological restoration by posing novel practice and research questions.

All lakes created on natural rivers are subjected to reservoir sedimentation. The construction of a dam significantly modifies the flow conditions of natural streams inside and downstream of an artificial lake. The sediment concentration is often high during the flood season, and the entering flow shows a greater density than the ambient fluid. Suspended load can therefore be carried along the reservoir bottom to the dam in the form of turbidity currents. This paper presents research results that help to better understand this physical phenomenon, which contributes to reservoir sedimentation. It is based on in situ measurements, a laboratory scale model of turbidity currents and numerical flow simulations. The study of a thousand-year flood in the Luzzone Reservoir in the Swiss Alps using the developed computer model revealed the potential of such a tool. In particular, the impact on the sediment deposits was analyzed. A valuable evaluation of the incidence of such a turbidity flow is presented and its ef...