A procedure for human safety assessment during hydropeaking events.

A method for human safety assessment on a hydropeaked river reach is proposed and applied to an Alpine river. The human safety analysis during hydropeaking events is of particular interest because most of the Alpine watercourses are affected by hydropower plant energy production that cause rapid and frequent flow alterations (hydropeaking), but at the same time these watercourses are used by the population for recreational purposes. In literature, many studies have focused on the effect of hydropeaking on the biota but a study of the interaction between a hydropeaking wave and human safety does not yet exist. The proposed procedure is characterized by the combination of hydraulic numerical simulations to study the characteristics of the flow field with a human safety analysis and is applied to a case study in north Italy. Human safety can be assessed in two different ways: one is by studying human stability during hydropeaking events and the other is exploring the possibility of a "target person" leaving the reach during hydropeaking waves, adapting proper escape strategies. For the escape strategy Dijkstra's algorithm is used, where the distance between adjacent nodes is defined as the difficulty (penalty) of moving from one node to the other. For this reason, an original set of penalty functions is proposed that takes into account the steepness (slope between two adjacent computational cells), the roughness, and the product between the water depth and flow velocity. The results show that the difficulty in escaping increases with the flow rate. Moreover, the areas where the human safety is very low are mainly located in the central part of the watercourse. The present work proposes a possible investigational tool to evaluate and parameterize the risk for the population during hydropeaking events through quantitative indices.

Hydropeaking mitigation project on a multi-purpose hydro-scheme on Valsura River in South Tyrol/Italy.

A hydropeaking mitigation project on Valsura River in the Italians Alps is described. The project is of particular interest due to several aspects. First of all, the Valsura torrent has unique morphological braiding characteristics, which are unique in the reach of Adige valley between Merano and Bolzano, and has a good reproduction potential for fish, especially in the terminal stretch along a biotope before its confluence with Adige River. Moreover, the Valsura hydropower cascade, which overall consists of six high-head hydropower plants, has an exceptional economic importance for the local hydropower industry. Lastly, the last HPP on the cascade is a multipurpose plant, so that interesting interactions between hydropeaking mitigation, irrigation supply and peak energy production are considered. The project started from a hydrological and a limnological measuring campaign and from an energetic, hydraulic and legislative framework analysis. The ecological findings are combined into a deficit analysis, founding the basis for the definition of a hydrological target state, which points to achieve a good natural reproduction for brown trout in the hydropeaked stretch, fulfilling at the same time the human safety conditions. Finally, mitigation Measures are described that at the same time comply with the following manifold aspects: a. maintenance of the requested target limits for fish reproduction; b. maintenance of the water release for the agricultural irrigation; c. enhancement of the flexibility of the hydropower plant's operation; d. reduction of the risk for local population. The paper compares operational and constructive mitigation measures and shows that constructive hydropeaking mitigation measures, for the present case study, can combine the positive effects of ecological improvement with higher safety standards and more flexible energy production.