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.

Piano Key Weirs (PKWs) are an alternative to linear overflow structures, increasing the unit discharge for similar heads and spillway widths. Thus, they allow to operate reservoirs with elevated supply levels, thereby providing additional storage volume. As they are relatively novel structures, few design criteria are available. Hence, physical model tests of prototypes are required. This study describes comprehensive model tests on a sectional set-up of several A-type PKWs, in which the relevant parameters were systematically varied. Considering data of former studies, a general design equation relating to the head–discharge ratio is derived and discussed. The latter is mainly a function of the approach flow head, the developed crest length, the inlet key height, and the transverse width. To extend its application range, case study model tests were analysed to provide a design approach if reservoir approach flow instead of channel flow is considered.

This paper presents the state-of-the-art on methods to estimate rock scour due to the impingement of plunging high velocity water jets. The following topics are addressed: empirical formulae, semi-empirical and analytical approaches, determination of extreme pressure fluctuations at plunge pool bottoms and, finally, the transfer of these pressure fluctuations in joints underneath concrete slabs or rock blocks. Available methods on rock scour have been thoroughly investigated on their ability to represent the main physical-mechanical processes that govern scour. This reveals lack of knowledge on turbulence and aeration effects, as well as on transient pressure flow conditions in rock joints. These aspects may significantly influence the destruction of the rock mass and should be accounted for in scour evaluation methods. Their relevance has been experimentally investigated by dynamic pressure measurements at modeled plunge pool bottoms and inside underlying one-and two-dimensional rock joints. Test results are described and discussed in Part II of this paper.

Turbidity currents are often the main process for the transport and deposition of the sediments in narrow, alpine reservoirs. These underwater avalanches with high concentration of suspended sediments follow the thalweg of the lake to the deepest area near the dam, where the sediments can affect the operation of the bottom outlet and the intake structures. To control the sedimentation within the reservoir, the effects of solid and permeable obstacles on the turbidity current were investigated with physical experiments and numerical simulations. In the physical experiments, the velocity distributions as well as the spatial and temporal evolution of the deposits were measured. The investigated measures were also simulated by means of a two-dimensional numerical model, based on the flow solver CFX-4.4. The investigations showed that turbidity currents can be influenced effectively by properly designed constructive measures. Based on the results of the physical experiments and numerical simulations, some desi...

Water supply systems (WWSs) are one of the main manmade water infrastructures presenting potential for micro-hydropower. Within urban networks, local decentralized micro-hydropower plants (MHPs) may be inserted in the regional electricity grid or used for self-consumption at the local grid level. Nevertheless, such networks are complex and the quantification of the potential for micro-hydropower other than that achieved by replacing pressure reducing valves (PRVs) is difficult. In this work, a methodology to quantify the potential for hydropower based on the excess energy in a network is proposed and applied to a real case. A constructive solution is presented based on the use of a novel micro-turbine for energy conversion, the five blade tubular propeller (5BTP). The location of the MHP within the network is defined with an optimization algorithm that maximizes the net present value after 20 years of operation. These concepts are tested for the WSS in the city of Fribourg, Switzerland. The proposed solution captures 10% of the city’s energy potential and represents an economic interest. The results confirm the location of PRVs as potential sites for energy recovery and stress the need for careful sensitivity analysis of the consumption. Finally, an expedited method is derived to estimate the costs and energy that one 5BTP can produce in a given network.