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The frequent pressure pulsations due to hydraulic transients in hydropower plants induce cyclic loading on the rock mass that may contribute to increased instances of block falls and increased risk of tunnel collapse over the power plant lifetime. This study focuses on understanding the effect of frequent start and stop sequences of hydropower in unlined pressure tunnels. For this purpose, data from a pore water pressure monitoring system is utilized, which was installed at the downstream end of the headrace tunnel at the 50 MW Roskrepp hydropower plant in southern Norway. The objective of this study is to analyze the recorded data and quantify the impact of the hydraulic transient on the surrounding rock mass in the unlined pressure tunnel. The monitoring of pressure data over several years clearly shows that frequent load changes could cause a considerable effect on the rock mass and constituent joint system. A delayed response of the pressure in boreholes in the rock mass compared with inside the tunnel is seen in all start and stop sequences and is considered to be the main reason for instability caused by transients. The response of pore pressure in boreholes is greatly influenced by the characteristics of joints. The results show that the start sequence and shorter shutdown duration exert a greater impact on rock mass as compared to the stop sequence and longer shutdown duration. Therefore, it is recommended to increase the shutdown duration so that the impact can be minimized to increase the tunnel lifetime. This study recommends implementing a more conservative design approach in tunnels with weak rock masses in projects that involve frequent load changes. [ABSTRACT FROM AUTHOR]

Many Norwegian rivers and lakes are regulated for hydropower, which affects freshwater ecosystems and anadromous fish species, such as sea trout (Salmo trutta). Lakes are an important feature of many anadromous river systems. However, there is limited knowledge on the importance of lakes as habitat for sea trout and how hydropower affects the behaviour of sea trout in lakes. To investigate this, we conducted an acoustic telemetry study. A total of 31 adult sea trout (532 ± 93 mm total length) were captured by angling in river Aurlandselva, Norway, and tagged between July 20 and August 12, 2021. The tags were instrumented with accelerometer, temperature, and depth sensors, which provided information on the sea trout's presence and behaviour in lake Vassbygdevatnet. Our results indicate that there was a large prevalence of sea trout in the lake during the spawning migration, and that the sea trout were less active in the lake compared to the riverine habitats. An increase in activity of sea trout in the lake during autumn might indicate that sea trout spawn in the lake. However, the discharge from the high-head storage plant into the lake did not affect the depth use or activity of sea trout in the lake. Furthermore, the large prevalence of spawners in the lake during autumn will likely cause an underestimation of the size of the sea trout population in rivers with lakes during annual stock assessment. In conclusion, our results could not find evidence of a large impact of the discharge on the behaviour of sea trout in the lake. [ABSTRACT FROM AUTHOR]

This article proposes and demonstrates a new classification system of fish population level effects of hydropeaking operations in rivers. The classification of impacts is developed along two axes; first, the hydromorphological effect axis assesses the ecohydraulic alterations in rivers introduced by rapid and frequent variations in flow and water level, second the vulnerability axis assesses the site‐specific vulnerability of the fish population. Finally, the population level impact is classified into four classes from small to very large by combining the two axes. The system was tested in four rivers in Norway exposed to hydropeaking, and they displayed a range of outcomes from small to very large impacts on the salmon populations. The river with a relatively high base flow and ramping restrictions scored better than rivers with the lower base flow or limited ramping restrictions, indicating that hydropeaking effects can be mitigated while maintaining high hydropower flexibility. Most effect factors could easily be calculated from timeseries of discharge and water level, whereas the use of hydraulic models to estimate potential stranding areas may require more work. The vulnerability factors are mainly qualitative and depend more heavily on expert judgments and are thus more uncertain. The system was deemed suitable for the purpose of supporting management decisions for rivers exposed to hydropeaking operations. It evaluates the severity of the additional pressures due to hydropeaking operations and proved useful to identify mitigating measures. While the system was developed for Atlantic salmon river systems, it could be adapted to other species or systems. [ABSTRACT FROM AUTHOR]

This paper describes an experimental campaign where a simplified test method. The Rapid Step-Rate Test (RSRT) has been investigated in a full-scale field setting. The test, originally developed to assess rock stresses for pressure tunnel considerations, had in an earlier laboratory study demonstrated a promising ability to assess the magnitude of fracture normal stress. The field campaign presented herein was therefore aimed at assessing the field applicability of this test. The field experiments were conducted inside the pressure tunnel of the Løkjelsvatn Hydroelectric Power Plant in Norway, under field conditions identical to those for which the test originally was developed. A total of 29 individual tests were conducted in 7 boreholes, providing 20 test cycles with interpretable test results. The stress estimates made from the test cycles not affected by the near-field stress of the tunnel showed good correlation with the magnitude of minimum principal stress found from a preceding hydraulic fracturing and over-coring stress measurement campaign. The experience from the field campaign suggests that the RSRT can represent an efficient and reliable method to assess the magnitude of minimum principal stress, particularly useful for the final design of unlined pressure tunnels. Highlights: A first field verification of a new flow-controlled hydraulic jacking test protocol, the Rapid Step-Rate Test, is presented The test protocol enables estimation of fracture normal stress through analysis of the pressure decline curve during fracture closure stages The onset of fracture closure can be identified as a distinct brake of slope, passing from an initial linear pressure decline to a more gradual decline [ABSTRACT FROM AUTHOR]

Hydroelectric power facilities can generate episodic total dissolved gas supersaturation (TDGS), which is harmful to aquatic life. We developed a decision tree-based risk assessment to identify the potential for TDGS at hydropower plants and conducted validation measurements at selected facilities. Applying the risk model to Norway's hydropower plants (n = 1696) identified 473 (28 %) high-risk plants characterized by secondary intakes and Francis or Kaplan turbines, which are prone to generating TDGS when air is entrained. More than half of them discharge directly to rivers (283, 17 % of total). Measurements at 11 high-risk plants showed that 8 of them exhibited biologically relevant TDGS (120 % to 229 %). In Austria and Germany, the analysis of hydropower plants was limited due to significant data constraints. Out of 153 hydropower plants in Austria, 80 % were categorized at moderate risk for TDGS. Two Austrian plants were monitored, revealing instances of TDGS in both (up to 125 %). In Germany, out of 403 hydropower plants, 265 (66 %) fell into the moderate risk, with none in the high-risk category. At a dam in the Rhine River, TDGS up to 118 % were observed. Given the uncertainty due to limited data access and the prevalence of run-of-river plants in Austria and Germany, there remains an unclarified risk of TDGS generation in these countries, especially at spillways of dams and below aerated turbines. The results indicate a previously overlooked potential for the generation of biologically harmful TDGS at hydropower installations. It is recommended to systematically screen for TDGS at hydropower installations through risk assessment, monitoring, and, where needed, the implementation of mitigation measures. This is increasingly critical considering the expanding global initiatives in hydropower and efforts to maintain the ecological status of freshwater ecosystems., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Martin Schletterer reports a relationship with TIWAG Tyrolean Hydropower that includes: employment. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Arctic rivers and water resources currently experience significant hydrological changes due to climate change and global warming. The flow regime alteration in Arctic rivers strongly influences the conservation and sustainability of the native biodiversity of the riverine ecosystem. The change in major characteristics of the daily and monthly flow regime of seven arctic rivers has been assessed in this study. The daily flow (40–120 years) at the outlet of Lena River, Yenisey River, Kolyma River, and Ob' River in Russia; Yukon River in the USA; Mackenzie River in Canada; and Tana River, Norway was used. Except for the Tana River, the rest of these rivers have been regulated. In addition, monthly flow alteration in the headwater of these rivers and below sixteen dams was assessed. In this research, we applied 'Indicator of Hydrologic Alteration' (IHA) and 'River Impact' (RI) methods to estimate daily monthly flow change in the river. Based on the daily analysis, the most significant change was observed for Yenisey and Ob rivers. The Kolyma hydropower shows the lowest impact, while the Shushenskaya Dam on Yenisey shows the highest impact on the flow regime. • The flow regime variation of seven major arctic rivers was analyzed. • The impact of 16 dams on the flow regime of the major arctic rivers was studied. • Winter streamflow of Arctic rivers increased significantly over the past 40 years. • The Shushenskaya dam on the Yenisey river showed the highest impact on flow regime. [ABSTRACT FROM AUTHOR]

Perspectives on the Environmental Implications of Sustainable Hydropower gathers scientific papers from three of the worlds most important hydropower producers to discuss aspects of sustainable hydropower and the means by which it can be studied and achieved. The papers examine the application and use of new technologies and protocols for studying hydropower, adaptive management and the implications and use of long-term data sets for minimizing hydropower impacts on fish populations. The papers include a cross section of biological and hydrological experts. The implicit among country comparisons highlight a number of common hydropower themes, particularly the need to expand from single species studies to include broader consideration of the ecosystem, the importance of maintaining habitat, trait and species diversity and the need for consistently collected long-term data sets. [ABSTRACT FROM AUTHOR]

Total dissolved gas (TDG) supersaturation downstream of hydropower plants may cause gas bubble disease (GBD) and harmful effects in fish. Little is known about tolerance levels of TDG supersaturation on Atlantic salmon (Salmo salar Linnaeus, 1758) in natural rivers. The present study investigated the effects of TDG supersaturation on the survival of Atlantic salmon smolts at two field sites in Norway. Here, we kept smolts in cages at increasing distances from hydropower plants known to cause TDG supersaturation and at control sites. We recorded fish mortality and examined for GBD using a stereo microscope. Mortality and symptoms of GBD commenced in fish exposed to an average of 108.3% TDG (maximum 111.0%, water depth 0.55 m) for 2 days. Significant differences in time before mortality at the control sites and test sites commenced at 110.2% TDG (maximum 111.8%) for 3 days. The study indicates that Atlantic salmon may be more vulnerable to TDG supersaturation than Pacific salmonids, which are considered at risk when the TDG is above 110%. In addition, the study provides important data to link effects caused by TDG in the laboratory and in the field. [ABSTRACT FROM AUTHOR]

Total dissolved gas supersaturation from dams and power stations is a chronic freshwater pollutant that is toxic to animals with aquatic respiration. Laboratory ecotoxicology experiments have revealed capacity for captive fishes to saturoregulate by moving deeper, but field ecotoxicology research is largely lacking. We instrumented 94 brown trout in the Rysstad basin of the Otra River, Norway, with depth sensor acoustic transmitters and monitored their movements for 10 months. We found that the depths used by the trout largely protected them from the effects of total dissolved gas supersaturation, which ranged from 96% to 133% total gas pressure during the study. The depth use of fish was affected by sun position, lunar phase and spatial position in the river (i.e., available depth), and there was an extremely weak effect of total dissolved gas supersaturation that was counterintuitive (i.e., positive slope, movement toward surface). Depth traces of the fish revealed that nine fish died during the study, mostly coinciding with the first wave of supersaturation, consistent with observations of untagged dead fish with signs of gas bubble trauma found on the river bottom during this period (May‐June). Overall, tagged trout exposure to total dissolved gas supersaturation depended on their use of depth, but responses to waves of extreme supersaturation at supraphysiological levels were weak and biologically insignificant, with individual variation and spatial position in the river most important in the model. Exposure to total dissolved gas supersaturation was mediated by individual differences in habitat use, which may be linked to activity and other traits that determine overall vulnerability to exposure to total dissolved gas supersaturation. [ABSTRACT FROM AUTHOR]

The meaning of riverine landscapes to society has evolved to serve our ever-changing needs, from harvesting and transporting resources to arenas for outdoor recreation and contemplation. From the 18th century, rivers have been important resources for industry and hydroelectric power. The objective of this study is to explore and describe the rhythms of everyday use of a river environment using multiple quantitative and qualitative methods, and to identify subjective, multiple and often competing relations. We use Lefebvre's concept of rhythmanalysis and Ingold's contextual approach as a tool for bridging scientific and methodological disciplines. Our results show a wide breadth in everyday activities and a dynamic relation between people and the river on multiple time scales. The use of the river environment appears orderly and predictable, but the wide spectrum of everyday users on different spatiotemporal scales is diverse and forms multiple rhythms at each locality. The partial lockdown in Norway in response to Covid-19 and the subsequent shifts in people's daily routines changed the rhythm of daily and weekly use patterns, and demonstrates how rhythms can change rapidly in the face of large-scale, societal agitation. We argue that rhythmanalysis is a useful analytical tool in interdisciplinary approaches to better understand the use and valuations of landscapes. • Approaches rural river everydayness through interdisciplinary rhythmanalysis. • Portrays the polyrhythms of nature and society. • Provides an example of empirical way to explore river environment complexity. • Managing landscape by an understanding of its polyrhythms, preventing arrhythmia. • Describe the contextual and dynamic relation between people and nature. [ABSTRACT FROM AUTHOR]

Load changes in hydropower plants result in significant pressure transients and unsteady flow in the waterway. It has been observed that instances of block falls in tunnels have increased in unlined pressure tunnels subjected to frequent load changes. To examine this problem, field instrumentation was conducted in the 3.5 km long unlined headrace tunnel of 50 MW Roskrepp hydropower plant in southern Norway. This article describes the methodology of instrumentation, presents the observations and findings. The monitoring clearly demonstrates that frequent load changes have a considerable effect in the rock mass consisting of system of joints. The observations show that pressure transients can travel deep into the rock mass irrespective of their time period. Moreover, pressure transients with longer time periods, i.e. mass oscillations, are seen to induce a higher hydraulic gradient between the rock mass and the tunnel itself. A delayed response from the rock mass is observed during pressure transients, which is the main cause of development of hydraulic gradient and additional pore pressure acting on the rock blocks. Hence, it is evident that the cumulative impact of small but frequent pressure gradients is significant and is responsible for increased instances of block falls over a long period of operation of the unlined tunnels of hydropower plants with frequent start–stop sequences. The overall impact is governed by pore pressure response of the jointed rock mass which depends on the conditions of joint geometry and joint wall properties. [ABSTRACT FROM AUTHOR]

Although regular curtailment of wind power has not been necessary in the Nordic power system so far, rapidly increasing wind power capacity means that it may be needed in the future. To estimate the amount of curtailment in the future Nordic power system we develop an hourly dispatch model based on open data. The model is validated against historical data and used to perform a case study for the Nordic power system in 2025 to estimate the amount of wind power curtailment under different assumptions. Curtailment is found to be below 0.3% of available generation for a 26 GW wind scenario and below 1.7% for a 33 GW wind scenario, when considering trade with neighbouring systems. The most important measures for decreasing curtailment are found to be increased transmission capacity, particularly between the areas in Sweden and those in Norway and Denmark, as well as flexibility of nuclear generation. Inertia requirements are found to have a limited impact on curtailments. • Annual wind curtailment with 26 GW wind power is found to be below 0.3%. • Inertia requirements are found to have minor impact on curtailment. • Transmission capacity from Sweden to Norway and Denmark reduces curtailment the most. [ABSTRACT FROM AUTHOR]

As Europe moves towards renewable energy, hydropower stands out as a renewable technology that can provide supply side flexibility through dispatchable electricity production. Several studies have investigated the flexibility hydropower can provide with a particular focus on the Nordic hydropower resources. Of all European countries, Norway has the largest hydropower resources and storage capacity. However, Norway also has a highly electrified heating sector, which means high electricity demand during winter when reservoirs are low. This paper uses EnergyPLAN to analyse how a shift from individual electric heating to district heating affects the flexibility the Norwegian energy system can provide to Europe. The analysis develops a 2015 reference scenario and two scenarios that introduce district heating based on biomass and heat pumps, respectively. Results show that district heating can decrease the maximum load on dammed hydropower facilities, thus freeing up capacity for potential export. Furthermore, the dammed hydropower facilities are able to balance the electricity demands in all hours of the year. However, the shift to district heating also increases forced export to drain reservoirs as domestic electricity demand is reduced. Also, the amount of import the system is able to handle is decreased under the modelled conditions. • A shift from electric heating to district heating frees up generation capacity. • A decrease in electricity demand leads to excess electricity production. • The amount of import the energy system can handle decreases with district heating. [ABSTRACT FROM AUTHOR]

Norway is the largest hydropower producer in Europe and provides currently 96% of domestic electricity supplies. Hydropower is a renewable and climate friendly source of energy, but causes an impairment on local environmental conditions, recreational use and aesthetics in and along impacted watercourses and lakes. Around 70% of the larger Norwegian watercourses and half of the country's total water-covered areas are regulated for hydropower production. By 2022, up to 430 hydropower licences will come up for revisions to implement the European Water Framework Directive in Norway. These have considerable potential to increase environmental and aesthetic conditions in Norwegian watercourses. We examine the decision-making of five completed licence revisions by means of document analyses of all relevant written sources, showing the content, methods and procedural qualities of the revision process. Despite case-specific differences, there are significant commonalities which form the basis for recommendations. Multi-criteria decision analysis (MCDA) can be used to improve the documentation of physical impacts and value judgements in hydropower decision-making processes. We analyse the perception of main interest groups with regards to the use of MCDA in future revisions. There exists a rather strong resistance to using MCDA due to a variety of political and regulatory reasons. [ABSTRACT FROM AUTHOR]

Abstract: Hydropeaking involves rapid changes in water flow, causing negative effects on aquatic organisms. To reduce these effects, hydropower licenses contain restrictions on hydropeaking. The owners of a hydropower plant are obliged to follow the requirements in the license. This study was conducted to understand the effect of environmental policies in small hydro licenses. We studied the occurrence of hydropeaking by analysing 256 high‐head, small Norwegian hydropower plants in relation to a set of characteristics that define each plant. We selected plants that were online during 2005–2014 and chose 2015 as a year for hourly production patterns. We counted the number of starts, that is, the moment when the hydro facility starts to produce energy, as an indicator of hydropeaking. Among the analysed plants, 75.8% had restrictions to practice hydropeaking. Production typically showed daily, weekly, and annual cycles though shapes varied depending on turbine type and location. The number of starts was independent on having or not having a license to practice hydropeaking. The average duration of periods with production and the average production in these periods were higher for plants without restrictions. The number of starts varied widely among plants. The number of starts was lower for installed Pelton turbines than for Francis and Kaplan turbines, which was in agreement with the characteristics of the turbines. Overall, these results show that hydropeaking restrictions given in the licenses are rarely followed. The high number of starts may be explained by failure in the grid system, improper maintenance, and financial interests. Their relative importance should be subject to further investigation. [ABSTRACT FROM AUTHOR]

The purpose of this study was to identify the factors that influence municipalities׳ participation in new hydropower development in Norway. Since Norway is pursuing the ways of realizing the political objectives related to the promotion of renewable energy, it is relevant to reconsider planning new hydropower developments. Due to political priorities there has been a boom in small scale hydropower development but very limited development has taken place in large scale hydropower during the last 10 years. Norway has a huge potential for small hydropower plants along with renovation and expansion of existing hydro plants. Municipalities in Norway are involved in hydropower generation in different ways. Municipalities have unique knowledge about the local environment and they communicate both with local communities, NGOs and energy companies regarding both positive and possible negative impacts of hydropower development. Thus it is important to investigate the municipal councils׳ attitude and participative behavior in increasing new hydropower plants in their regions. It is also important to determine the challenges that municipalities are experiencing in that regard. In order to identify factors influencing municipality׳s participative behavior in new hydropower development the motivation–opportunity–ability (MOA) framework was used. Several hypotheses were proposed. To test the hypothesized relationships, a survey was conducted and data were collected from municipalities across Norway. The findings suggest that the extent to which municipalities participate in the new hydropower development process depend on motivation, opportunity, and ability to participate. The role of pre-existing beliefs and attitudes were not found to have an influential role in participation, however opportunity proved to be a key determinant. Though municipalities have positive attitude towards new development but the benefit they receive and their opportunity to participate during the process are found to be the important determinants in increasing their participative behavior. [ABSTRACT FROM AUTHOR]

Abstract: Renewable energy is a cornerstone of German climate change policies. Germany has adopted particularly ambitious renewable energy targets, and is now implementing an Energiewende – a transition to a nuclear-free and low-carbon energy system. The transition could be eased through European cooperation. This article investigates the economic, political, environmental and technological factors that act as drivers and barriers to renewable energy cooperation between Germany and Norway. The article finds that German actors see Norwegian electricity as a means for enhancing the stability of their electricity system as Germany shifts to a greater reliance on renewables. In Norway the picture is more mixed. Norwegian state-owned electricity producers and grid operators are interested in cooperation largely out of profit motives, but expect Germany to create a favorable environment for investors. Energy-intensive industries and consumers on the other hand, are afraid that more electricity cooperation with Germany will raise electricity prices. The Norwegian environmental movement is split on the issue. Parts of the movement see renewable energy cooperation as an important step towards a European low-carbon energy future. Nature and outdoor organizations, however, argue that new renewable energy infrastructure, including pumped-storage hydropower, will result in major environmental impacts. If cooperation is to be achieved, these economic and environmental concerns will have to be taken seriously. [Copyright &y& Elsevier]

It is well established within both the economics and power system engineering literature that hydropower can act as a complement to large amounts of intermittent energy. In particular hydropower can act as a "battery" where large amounts of wind power are installed. In this paper I use simple distributed lag models with data from Denmark and Norway. I find that increased wind power in Denmark causes increased marginal exports to Norway and that this effect is larger during periods of net exports when it is difficult to displace local production. Increased wind power can also be shown to slightly reduce prices in southern Norway in the short-run. Finally, I estimate that, as much as 40 percent of wind power produced in Denmark is stored in Norwegian hydropower magazines. [ABSTRACT FROM AUTHOR]

Abstract: A vanguard project is an effective mechanism for testing new opportunities to deploy existing technologies into new markets in an effort to realize growth. Typically such endeavors are motivated by organizational needs to generate new knowledge and learning to develop or renew existing capabilities of the firm. In the case of Norwegian independent power producers (IPP), a recent trend to achieve company level growth is by expanding hydropower operations into international markets thus testing theoretical foundations of vanguard projects. Whilst many other European IPPs have internationalized stepwise in a pan-European context, Norwegian IPPs have chosen to pursue non-core European markets for international expansion. This paper serves to underscore the innovative globalization strategy shifts amongst Norwegian IPP by underpinning the challenges and opportunities of these activities in developing and emerging countries. To achieve this research objective triangulation of quantitative and qualitative data is utilized. Primary qualitative data includes exploratory case studies at the firm level, whereas quantitative data includes a national survey amongst Norwegian IPPs. Theoretical considerations lie within how such vanguard projects allow for core business activities to persist by diversifying geographically into dissimilar markets. The result of this research stream identifies the degree to which Norwegian IPP actors are actively developing such vanguard projects in which geographic locales of emerging markets. The mixed method approach results delineate how Norwegian IPPs are internationalizing and what the managerial implications are for entrepreneurs and IPPs alike. [Copyright &y& Elsevier]

The effects of induced water level fluctuations and introduction of the mysid Mysis relicta Lovén on population structure of brown trout, Salmo trutta L., and Arctic charr, Salvelinus alpinus (L.), were studied during 1953–1995 in Limingen hydroelectric reservoir, Norway. The main response was a marked reduction in catch-per-unit-effort (CPUE) for trout and charr, probably caused by reduced recruitment following increased variation in water level. For both species, mean length decreased until 1967 and increased thereafter, whereas mean mass-at-length increased for the whole period. Both length and mass-at-length were negatively correlated with CPUE. The increases in mean length and mass-at-length were probably because of reduced competition following the reduced recruitment. Mysis relicta has become an important food item for charr but not for brown trout, but the increases in mean length and mass-at-length of charr started prior to the appearance of M. relicta in the charr diet. [ABSTRACT FROM AUTHOR]

We studied reindeer (Rangifer tarandus tarandus) distribution in relation to possible travel barriers (roads and power lines) in south-central Norway, 1997-2000, using lichen biomass as an indicator of reindeer use. We recorded lichen cover on both sides of potential barriers within comparable habitat in 42 sites for 3 different reindeer herds. We used cover-biomass regressions to assess the relationship between lichen cover and biomass. In 2 of the regions, lichen biomass was 5.3 times and 2.8 times higher in areas isolated by.2 parallel power lines and an adjacent winter-closed road compared to biomass on the other side of the potential barrier. In a third region, lichen biomass did not vary significantly between areas on either side of a single winter-closed road. Lichen biomass data suggested that wild reindeer used both sides of a closed road in winter, whereas 2 parallel power lines and a winter-closed road in combination reduced reindeer migration and resulted in very different grazing pressures on either side of the power lines, even 30 years after the power lines were constructed. Construction of power lines, and particularly parallel power lines, should thus be avoided in wild reindeer habitat. Fragmentation of wild reindeer ranges in Norway results in a substantial reduction in available ranges and traditional migration routes between important seasonal ranges, with a likely overall reduction in carrying capacity. [ABSTRACT FROM AUTHOR]

The main objective of this study is to investigate the effect of hydropower plant operation on the long-term stability of unlined pressure tunnels of hydropower plants in Norway. The authors analyzed the past production data of some hydropower plants to find out the number of starts/stops and the frequency and magnitude of load changes. The study demonstrates that an average of 200–400 start/stop events are occurring per turbine per year for the analyzed period, with an increasing trend. Currently, 150–200 large load changes per turbine smaller than 50 MW are occurring every year, and this is expected to increase by 30–45% between 2025 and 2040 for one of the studied power plants. Most importantly, the monitored pressure transients and pore pressure response in the rock mass during real-time operation at Roskrepp power plant are presented. A new method is proposed to calculate and quantify the hydraulic impact (HI) of pressure transients on rock joints and the effect of duration of shutdown/opening, which is found to be the most dominant parameter affecting the magnitude. The results show that faster shutdown sequences cause unnecessary stress in rock mass surrounding pressure tunnel. The hydraulic impact (HI) can be more than 10 times higher when the shutdown duration is reduced by 50 percent. The study recommends that duration of normal shutdowns/openings in hydropower plants should be slower so that hydraulic impacts on the rock joints are reduced and cyclic hydraulic fatigue is delayed, prolonging the lifetime of unlined pressure tunnels and shafts. [ABSTRACT FROM AUTHOR]

The friction loss in a part of the rock-blasted unlined tunnel of the Litjfossen hydropower plant in Norway was determined from experimental and numerical studies. Remote sensing data from the prototype tunnel provided the input data for both the numerical model and the construction of a 1:15 scale model with an innovative milling approach. The numerical simulations were based on the solution of the Reynolds-averaged Navier–Stokes equations using the CFD program OpenFoam. Head loss measurements in the scale model were carried out by means of pressure measurements for a range of discharges and were compared against the results of the numerical model. The measured data were used to determine the Darcy–Weisbach and Manning friction factors of the investigated tunnel reach. The high-resolution remote sensing data were also used to test the applicability of existing approaches to determine the friction factor in unlined rock blasted tunnels. The results of the study show the usefulness of the chosen hybrid approach of experimental investigations and numerical simulations and that existing approaches for the determination of head losses in unlined tunnels need to be further refined. [ABSTRACT FROM AUTHOR]

This paper presents a technical review of the existing pumped storage plants in Norway. The power system is changing towards integrating more and more renewable energy, especially from variable renewable energy sources, leading to new challenges for the security of supply, power, frequency, and voltage regulation. Thus, energy storage options are a highly researched topic in the current situation. Even though there are many energy storage technologies, most are optimal for short term grid balancing, and few are capable of providing long term (weekly or seasonal) storage. One exception is pumped storage, a mature technology capable of delivering both short term and long term energy storage. In this paper, the ten existing pumped storage plants in Norway are presented, several of which are capable of seasonal energy storage. The Norwegian knowledge and experience with pumped storage plants technology is provided as a basis for future research within the field. The review provides information about energy production and storage capabilities, construction costs, specific costs per kW and stored kWh, electromechanical installation, technical specifications, and operational experience with focus on the design of the tunnel system layout. The data presented in this review are unique and previously unpublished. A discussion and conclusions regarding the current situation, trends, and future outlook for pumped storage plants in Norway within the European power market are provided. [ABSTRACT FROM AUTHOR]

The globally increasing pace of ecosystem degradation makes it necessary to develop efficient restoration programmes. A reliable tool for estimation of the remaining time to recovery is an important component of such a programme. In this study, we explore the performance of the novel, ordination regression-based approach (ORBA) for prediction of time to recovery. We applied ORBA to a dataset of plant species composition data from ten spoil heap sites in S Norway, resulting from hydropower development. Five study sites were situated in the alpine and five in the boreal bioclimatic zone, the latter group showing large between-site variability of climate, time since disturbance (age) and restoration treatments. The vegetation of spoil heaps was recorded at two time-points, while that of the surroundings of each spoil heap was recorded once, to serve as a reference. We obtained time-to-recovery predictions based on ordination of the full dataset and of two data subsets that represented alpine and boreal sites, respectively. The vegetation of all spoil heaps became more similar to the vegetation of their surroundings over time. In many cases, linear models described the temporal pattern less well than asymptotic models. The latter models predicted slow recovery for all sites, but showed large variation in time to recovery among the boreal sites. In some of the boreal sites, we observed extremely species-poor plots and many infrequent species. Moreover, in one site we observed apparent mismatch between observed vegetation development and the underlying model of increasing similarity to surroundings. We ascribed these cases to suboptimal restoration practises, and for them, non-significant ORBA models resulted. Our findings support the conclusions of previous studies; that ORBA is a robust method for predicting time to recovery over a wide range of restoration projects. Its output – predicted time (years) to recovery – is easily communicated and may be useful in evaluating the speed and direction of restoration programmes. However, our results also demonstrate the importance of carefully assessing the properties of datasets (e.g. plotwise species richness) subjected to ORBA analyses. Unlabelled Image • Predictions of restoration success are useful in restoration of degraded habitats. • ORBA (ordination regression-based approach) offers time-to-recovery predictions. • Times to recovery were predicted for alpine and boreal hydropower spoil heaps. • Dataset properties and adequacy of underlying models affect time-to-recovery predictions. • ORBA appears robust and promising but further exploration is encouraged. [ABSTRACT FROM AUTHOR]

An increase of tightly integrated, renewable energy sources with highly varying production leads to a greater need for flexible hydropower plants to "balance" the intermittent production from these sources. From a systems perspective, the intermittency aspect constitutes a disturbance, while the tight integration leads to a multivariable systems, both of which causes increased challenges for good control. This instigates the need for a model based analysis and synthesis tool which can describe dynamic phenomena, supports multiphysics problems, and allows for immediate use in advanced control analysis and design. Previously, an open source Hydro Power Library (OpenHPL) have been developed within the multiphysics Modelica eco-system which satisfies the above requirements: OpenHPL contains a set of model units relevant for hydropower systems, as well as examples of tools for analysis of these models for control purposes. Thus far, OpenHPL has been validated by comparison against other simulation tools. However, a real test of OpenHPL is to use it to describe a real hydropower plant using minimal plant information, to tune model parameters against experimental data, and to validate the model. As a case study, experimental data from the Trollheim hydropower plant in Norway have been made available, and used to test OpenHPL. By flow sheeting a hydropower model in OpenModelica using OpenHPL, the model can be simulated from within a script language (Python via the OMPython API, Julia via the OMJulia API) and further analyzed using analysis tools in the script language. Based on default model parameter suggestions from OpenHPL, least squares model fitting was carried out in Python, and the model was validated with good model fit. Important parts of the modelling phase were the development of a new friction model for the Francis turbine, and iterations on the description of the turbine outlet geometry. The results are complemented with a discussion of possible uses of the model. [ABSTRACT FROM AUTHOR]