Diego Tonolla

Chapter 1 – Introduction to European Rivers

Publisher Summary Rivers recognize no political boundaries. This is particularly true for Europe, which has over 150 transboundary rivers. For example, the Danube is the 29th longest river globally and it drains parts of 19 countries and 10 ecoregions. Further, 8 of the 10 largest catchments in Europe are in the eastern plains of Russia and the Ukraine and information on their present status is highly limited. Europe also has a long history in river training with most rivers being severely fragmented, channelized, and polluted. The European Union launched an ambitious program called the Water Framework Directive (WFD), which requires a catchment management plan for all major European rivers for achieving “good ecological status” by 2015. This chapter provides a comprehensive overview of all major European catchments included in the book, starting with the bio-geographic setting, with an emphasis on physiography, hydrology, ecology/biodiversity, and human impacts.

A conceptual framework for hydropeaking mitigation.

Hydropower plants are an important source of renewable energy. In the near future, high-head storage hydropower plants will gain further importance as a key element of large-scale electricity production systems. However, these power plants can cause hydropeaking which is characterized by intense unnatural discharge fluctuations in downstream river reaches. Consequences on environmental conditions in these sections are diverse and include changes to the hydrology, hydraulics and sediment regime on very short time scales. These altered conditions affect river ecosystems and biota, for instance due to drift and stranding of fishes and invertebrates. Several structural and operational measures exist to mitigate hydropeaking and the adverse effects on ecosystems, but estimating and predicting their ecological benefit remains challenging. We developed a conceptual framework to support the ecological evaluation of hydropeaking mitigation measures based on current mitigation projects in Switzerland and the scientific literature. We refined this framework with an international panel of hydropeaking experts. The framework is based on a set of indicators, which covers all hydrological phases of hydropeaking and the most important affected abiotic and biotic processes. Effects of mitigation measures on these indicators can be predicted quantitatively using prediction tools such as discharge scenarios and numerical habitat models. Our framework allows a comparison of hydropeaking effects among alternative mitigation measures, to the pre-mitigation situation, and to reference river sections. We further identified key issues that should be addressed to increase the efficiency of current and future projects. They include the spatial and temporal context of mitigation projects, the interactions of river morphology with hydropeaking effects, and the role of appropriate monitoring to evaluate the success of mitigation projects.

Combining active and passive hydroacoustic techniques during flood events for rapid spatial mapping of bedload transport patterns in gravel-bed rivers

With 7 figures Abstract: Turbulent flow in rivers and the associated movement of sediment creates unique underwater sound- scapes that can be measured passively with hydrophones while Acoustic Doppler Profilers (ADP) are an active form of hydroacoustic sampling that can be used to provide a surrogate measurement of Apparent Bedload Veloc- ity (ABV). In our study, longitudinal profiles of ADP and sound were simultaneously measured, while floating the river in a raft on the Nyack Floodplain of the Middle Fork of the Flathead River, USA during flood events exceeding bankfull conditions. In addition, similar measurements were carried out on the Kootenai River during a prescribed flood release aimed at mobilizing gravel bed sediment to positively impact White Sturgeon spawn- ing. Both data sets revealed spatially explicit zones of coherent ABV and bedload intensity (sound) over the two 12 km river segments. The ability to remotely and in real-time assess bedload transport for large gravel-bed rivers, on the floodplain scale, is a missing piece of information important for basic ecological understanding and applied science, specifically management decisions regarding regulated rivers worldwide. With these data sets we dem- onstrate a new methodology for rapid real-time spatial surveying of bedload transport in large gravel-bed rivers.

Effects of river bank heterogeneity and time of day on drift and stranding of juvenile European grayling (Thymallus thymallus L.) caused by hydropeaking.

High-head storage hydropower is deemed to be the ideal renewable energy source in Alpine regions to meet the increasing demand for daily peak electrical energy. However, this mode of operation - called hydropeaking - can imply severe hydrological and hydromorphological consequences for river ecosystems, affecting fish populations by e.g. drift and stranding of young life stages. Several fish-stranding experiments using physical models have been performed in the past, but until now very little is known about influences of time of day or gravel bank heterogeneity. We performed experiments during late summer 2013 with juvenile European grayling (Thymallus thymallus) (mean length: 53mm) in a nature-like experimental channel enabling hydropeaking simulations. In the first experiments (n=21) we observed relative drift and stranding rates for a single hydropeaking event focusing on the effect of time of day on a homogenous gravel bank. The second test series (n=15) focused on two dewatering potholes installed as potential traps. Additional experiments (n=6) were done with a reduced downramping rate to gain information about potential mitigation effects on stranding risk. During daytime and decreasing water level, we observed low drift rates of 15% and stranding rates below 5% in dewatering potholes and on homogenous gravel banks. However, in the presence of dewatering potholes, nighttime drift rates were about three times and stranding rates about ten times higher than on the homogenous gravel bank. A lowered downramping rate reduced drift to about a quarter and almost eliminated nocturnal stranding risk. These results might be used to effectively regulate water releases from high-head storage hydropower plants in a more suitable way for sensitive life stages of fish. Reducing the downramping rate or shifting peaks to daytime can reduce negative effects of hydropeaking in consideration of the morphological character of affected rivers.

Evaluation of mitigation measures to reduce hydropeaking impacts on river ecosystems – a case study from the Swiss Alps

New Swiss legislation obligates hydropower plant owners to reduce detrimental impacts on rivers ecosystems caused by hydropeaking. We used a case study in the Swiss Alps (hydropower company Kraftwerke Oberhasli AG) to develop an efficient and successful procedure for the ecological evaluation of such impacts, and to predict the effects of possible mitigation measures. We evaluated the following scenarios using 12 biotic and abiotic indicators: the pre-mitigation scenario (i.e. current state), the future scenario with increased turbine capacity but without mitigation measures, and future scenarios with increased turbine capacity and four alternative mitigation measures. The evaluation was based on representative hydrographs and quantitative or qualitative prediction of the indicators. Despite uncertainties in the ecological responses and the future operation mode of the hydropower plant, the procedure allowed the most appropriate mitigation measure to be identified. This measure combines a basin and a cavern at a total retention volume of 80,000m3, allowing for substantial dampening in the flow falling and ramping rates and in turn considerable reduction in stranding risk for juvenile trout and in macroinvertebrate drift. In general, this retention volume had the greatest predicted ecological benefit and can also, to some extent, compensate for possible modifications in the hydropower operation regime in the future, e.g. due to climate change, changes in the energy market, and changes in river morphology. Furthermore, it also allows for more specific seasonal regulations of retention volume during ecologically sensitive periods (e.g. fish spawning seasons). Overall experience gained from our case study is expected to support other hydropeaking mitigation projects.

Projekte und Praxis

Im Rahmen der Entleerung des Stausees Raterichsboden (Berner Oberland, Schweiz) wurden verschiedene gewasserokologische Schutzmasnahmen realisiert. Fur den Erhalt des Seeforellenjahrgangs 2014/15 entwickelte die Fachstelle Okologie der Kraftwerke Oberhasli AG ein mobiles fischschonendes Leitsystem fur aufsteigendeWandersalmoniden, um die laichbereiten Seeforellen in ein Nebengewasser umzuleiten. Im Praxistest konnte sowohl die okologische Funktionsfahigkeit als auch die Hochwassersicherheit nachgewiesen werden. Das Leitsystem konnte auch fur andere fischokologische Fragestellungen adaptiert werden.

Schwall und Sunk — ein kurzer Überblick

Im vorliegenden Artikel wird versucht, den aktuellen Wissenstand zu den Auswirkungen von Schwall und Sunk auf die aquatische Gemeinschaft zusammenzufassen. Künstliche Pegelschwankungen verursachen kurzund langfristige Auswirkungen auf die Fließgewässerökologie. Auf Basis von Indikatoren lassen sich diese Auswirkungen bis zu einem gewissen Grad abschätzen und daraus möglichst e ziente Sanierungsmaßnahmen ableiten. Abschließend wird der Stand der Schwallsanierung in der Schweiz kurz beschrieben.