Good international practice for mitigating hydropower impacts on aquatic ecosystems

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J

Himalayan Aquatic Biodiversity and Hydropower:

Review and Recommendations

Atle Harby, Ana Adeva-Bustos and Marcell Szabo-Meszaros

SINTEF Energy Research, Water Resources

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2 Himalayan aquatic biodiversity and hydropower:Review and Recommendations

Report

Good international practice for mitigating hydropower impacts on aquatic ecosystems

Himalayan aquatic biodiversity and hydropower:

Review and Recommendations

KEYWORDS:

Hydropower Aquatic ecosystems Impacts

Mitigation measures

VERSION

Final version ^DATE2020-12-01

AUTHOR(S)

Atle Harby, Ana Adeva-Bustos and Marcell Szabo-Meszaros

CLIENT(S)

The World Bank CLIENT’S REF.

Pravin Karki

PROJECT NO.

502002543 NUMBER OF PAGES:

34

ABSTRACT

This report gives an overview of the mitigation approaches to address the challenges or impacts of hydropower on the aquatic biodiversity: altered flow regimes, depleted habitats and obstructed migration of species. This report also gives an overview of mitigation measures related to fish stocking. Good International solutions and good practice to mitigate negative impacts are suggested and illustrated with some examples.

PREPARED BY

Atle Harby ^SIGNATURE

CHECKED BY

Bendik Hansen ^SIGNATURE

APPROVED BY

Knut Samdal ^SIGNATURE

REPORT NO.

2020:01331 ^ISBN 978-82-14-064285 CLASSIFICATION

Unrestricted CLASSIFICATION THIS PAGE

Unrestricted

Bendik Hansen (Dec 1, 2020 16:22 GMT+1)

Bendik Hansen

Knut Samdal (Dec 1, 2020 19:15 GMT+1)

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Table of content

Preface 4

What is in this report? 4

Executive summary 5

1. Introduction 7

2. Diagnosis of impacts 8

2.1 Hydropower types 9

3. Good practice methods to mitigate impacts 10

3.1 Legislation, regulation and strategic planning 10

3.2 Mitigation hierarchy 12

3.3 Mitigation measures and decision management 13

4. Specific mitigation measures 14

4.1 Flow regime and water temperature 15

4.2 Habitat 18

4.3 Upstream fish migration 21

4.4 Downstream fish migration 22

4.5 Fish stocking to mitigate declining populations 29

5. Good practices in planning processes 32

6. References and key documents 33

Front page photo: Marshyangdi hydropower dam in February 2020 (Photo: Atle Harby).

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Preface

This report is written for the World Bank supported project "Himalayan aquatic biodiversity and hydropower: Review and Recommendations." The objective of the study was to review and

summarize current good international practice for mitigation of hydropower impacts on fish aquatic biodiversity and hydro-morphology, focusing on fish populations and their habitats. The measures selected have been reported as good practice to facilitate an adequate design, management, and operation of hydropower projects, enabling sustainable management of hydropower production meanwhile mitigating impacts on, and conserving the natural environment in riverine ecosystems.

SINTEF Energy Research was responsible for writing this summary report, supported by the team engaged in the project "Himalayan aquatic biodiversity and hydropower: Review and

Recommendations": comprised of Leeanne Alonso, Nikita Pradhan, Deep Shah and Rakesh Yadav, as well as Pravin Karki and Nicholas Zmijewski from the World Bank.

The report does not rely upon a comprehensive use of references. However, most statements are based on scientific journal articles, reports and information combined with the authors own experience and judgement.

What is in this report?

This report provides a brief introduction to aspects related to the diagnosis of hydropower impacts on ecosystems and aquatic biodiversity with a focus on fish. The main part of the report focuses on mitigating impacts from hydropower which are described in several categories and illustrated by case studies from good international practice.

The report is meant to provide an overview and guide readers from policy makers, authorities and the hydropower sector towards more detailed information when needed. This report does not give a comprehensive description or many technical details. Instead, a list of important and good

information, guidance, reports, and articles for further reading and information is provided.

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Executive summary

Hydropower may change flowing river sections to ponds and lakes upstream of the dam, alter flow and morphology in downstream reaches and bypassed rivers, causing direct mortality of aquatic species, changes in habitat conditions and introduce barriers for fish migration. Hydropower operations change the natural flow regime, especially power plants that operate with rapid and frequent variations in flow, so-called hydropeaking.

Hydropower projects that will result in significant residual impacts should be considered unsuitable for future development or mitigated if already constructed. For projects for which residual impacts will accrue, a key element is to find cost-effective mitigation measures, as it is important to balance the needs for electricity generation and a sustainable ecosystem, simultaneously.

It is challenging to mitigate all the impacts of hydropower, but there are many mitigation measures that can be implemented without compromising the total hydropower production or its operation.

When mitigation measures lead to loss of power production or restrictions in how to operate, the balance between benefits and impacts need to be assessed to make good decisions. Many hydropower and dam projects also serve other purpose than only electricity production, such as domestic, industrial and agricultural water supply, flood control and navigation. These services must also be included and balanced with needs for the aquatic ecosystem when appropriate. Degradation in the aquatic ecosystem may also have direct and indirect costs both on a local and a larger scale.

This report provides an overview of main points to consider when planning and implementing mitigation measures, and it identifies several examples of good practice mitigation measures. As each hydropower project is unique, and each river has specific aquatic ecology, it is important to select mitigation measures and adapt them to the local conditions. Good practice examples may be used as guidance in the process.

The mitigation hierarchy provides a structured approach to how to prioritize mitigation measures.

The best solution is always to design or retrofit a project to avoid negative impacts. If this is not possible, mitigation or restoration measures to minimize the impact should be implemented. As a last remaining option, compensation measures can be implemented.

Authorities may use legislation, regulation, strategic planning, licensing, monitoring, and

enforcement to ensure that aquatic ecosystems and biodiversity are taken care of in hydropower projects. Licenses and permits given to operate the power plants and produce hydropower should include terms and conditions to mitigate impacts on the environment, and there should be monitoring and penalties for non-compliance to the terms.

Impacts on aquatic ecosystems and biodiversity must be evaluated for each individual hydropower project. However, it is equally important to consider the status, impacts and mitigation measures in the larger area. Cumulative impacts of multiple large-scale developments, such as hydropower projects and dams, pose a significant risk to fish migration as downstream dams may block the access to upstream habitats.

Main conclusion:

To meet good international practice, countries should make a master plan for where to develop hydropower. All hydropower projects should release e-flows to diverted reaches and have two-way fish passage facilities. A monitoring program should be implemented to measure the effectiveness of mitigation measures, supporting adaptive management.

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As mitigation measures are being implemented, it is strongly recommended to monitor and evaluate their effect and, where warranted, reconsider and redesign measures. This is what is called adaptive management, a structured, iterative process of robust decision making to reduce uncertainty over time.

The main solutions to mitigate negative impacts from hydropower on the aquatic ecosystem are listed below, as our recommendations for decision makers, authorities and hydropower companies:

Figure 1. Introducing gravel and stones to improve shelter and habitat conditions for fish in a bypassed section of a river in Norway. The re-design of the riverbed creates variation and suitable habitats for different species and sizes of fish and invertebrates (Photo: Ulrich Pulg).

• Alterations of flow and water temperature can be mitigated by releasing e-flows of a suitable volume.

• Stones, gravel, current deflectors, construction of riffles and pools and other structural measures can mitigate degraded habitats together with some release of e-flow.

• Fish must be able to move safely past dams. Guiding devices and fine trash racks can help fish move downstream, while fish ladders and nature-like fishways help them move upstream.

• Fish stocking must be seen in combination with other measures, and it is must be managed without compromising natural fish populations.

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1. Introduction

Most hydropower projects will affect both aquatic and terrestrial biodiversity, and they will have an impact on multiple stakeholders and users. Examples of this are how migratory fish are being affected by dams blocking the river, by reduced flow in a bypassed section of the river downstream the dam where water is diverted, and fisheries communities being affected by the impact on fish population stocks.

It is often common to find or develop several hydropower projects in the same catchment.

Therefore, it is very important to consider the impacts on the whole catchment, as well as how each single project contributes to catchment-wide impacts. An example is how a single dam in the downstream section of a river may impact the fish species composition in river reaches upstream if the dam blocks migratory fish from ascending to their natural habitats further upstream.

This report focuses on the impacts of hydropower development on aquatic biodiversity with a special focus on fish at single hydropower projects. We strongly recommend assessing and diagnosing impacts considering the hydropower type and the location of the powerhouse, the target species and the mitigation objective, among other important aspects, and to plan mitigation measures for each hydropower project site following the mitigation hierarchy with consideration to other users and stakeholders, as well as taking a holistic view of the whole catchment.

This report presents impacts of hydropower on aquatic ecosystems and how to mitigate it in two main parts. The diagnosis of the hydropower impacts is presented first, focusing on fish. This part includes general topics for all kinds of impacts, including legislation, mitigation hierarchy and decision management. A description of good practice with examples follows, classified in five categories:

• Flow and temperature

• Habitat

• Upstream migration

• Downstream migration

• Fish stocking

After each category, examples of international good practice of mitigation is provided, including a description of the impacts, the mitigation measures applied, and the lessons learned. At the end of the report the reader will find a section with conclusions and a short discussion about good practices in adaptative management and holistic views of both hydropower development and the aquatic ecosystem.

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2. Diagnosis of impacts

Hydropower is a site-specific technology developed where the topography and hydrology are favourable. Hydropower plants require construction of a dam or weir, generally obstructing fish movements. Habitat are altered upstream of the dam, turning running water into ponded reaches.

Downstream of the dam, hydropower operation imposes changes in flow and sediment transport, impacting habitats. Biology and composition of fish populations are unique to each site. As such, the environmental problems and the related measures are also very specific to each location, posing challenges to presenting generic measures for all possible sites.

To identify the impacts from hydropower, it is recommended to adapt a systematic approach following Environmental and Social Impact Assessment (ESIA) methods. Many institutions,

associations, and governments (including Nepal⁶) issue guidelines for ESIA. A good example on how to diagnose impacts from hydropower and how to mitigate them is the environmental design method, which was developed to mitigate impacts from hydropower on salmon populations⁷. The focus is to identify the bottlenecks, i.e. the main factors having an important impact on fish. When the diagnosis is established using specific tools, it is possible to design the most appropriate mitigation measures considering the hydropower production (Figure 2).

Figure 2 The structure of an environmental design concept for salmon in hydropower rivers (modified from Forseth and Harby 2014⁷), focusing on identifying the bottlenecks to be mitigated.

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2.1 Hydropower types

Hydropower are normally grouped in three categories: Storage (or reservoir), Run-of-the River (RoR) and pumped storage (PHS) plants. A storage hydropower project will generally allow much larger changes in flow than a Run-of-the River plant. However, they can both provide hydropeaking although RoR plants will not always have sufficient water available to peak production over longer continuous periods.

For understanding the environmental impacts of hydropower, it is necessary to know the location of the powerhouse. If the powerhouse is located further downstream, a section of the river will be bypassed as water are diverted away. If the powerhouse is located at the foot of the dam, there is no diversion of water. Figure 3 illustrates the different powerhouse.

A hydropower project will influence and give direct impacts to the following river reaches:

• Reservoir or ponded reach upstream the dam. The impounded or backwater area can vary between several hundred meters to several hundred km in the extreme cases.

• Bypassed or diverted river section river section if the powerhouse is not located at the foot of the dam. This section can vary from just 100m to many km.

• Downstream reach, i.e. downstream the outlet of the powerhouse. The effects of the dam and hydropower operations can be seen for several km up to the whole way to the ocean or next lake or reservoir.

Different types of mitigation measures are relevant for these impacted river reaches, whereas some measures may apply to all reaches. For instance, e-flows should be released to bypassed sections to ensure a significant flow, whereas hydropeaking impacts and mitigation is necessary for downstream sections.

Figure 3. Different powerhouse location at the foot of the dam (left) or further downstream (right), leaves the river with a "bypassed reach" (right). Both situations have a "downstream reach" where the flow is totally or partly controlled by the turbined water.

Rivers with multiple power plans in a series are referred to as cascaded systems, these may include modifications or combinations of the hydropower types presented in Figure 3.

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3. Good practice methods to mitigate impacts

This report focuses on general aspects for good and successful practice of mitigation measures.

Successful mitigation of hydropower impacts on the aquatic ecosystems and biodiversity are not only dependent on technical solutions. It is also important that legislation and regulation are effective and provides the right incentives and impose appropriate obligations to hydropower plant owners to actually implement mitigation measures. The effectiveness of mitigation measures needs to be regularly and consistently monitored and subsequently evaluated for further reassessment and potentially redesign following the mitigation hierarchy over again.

3.1 Legislation, regulation and strategic planning

Providing electricity to enable society to function is essential in all countries, and the development of electricity generation, transmission and distribution is, therefore, regulated and controlled by

governments in most countries. As hydropower projects are often considered essential in such developments, it is important to incorporate strategic planning, permitting, licensing and surveillance in national legislation. A good strategy is to develop a Master Plan at a country level to guide

hydropower development to the most suitable sites with respect to power potential, economy, and environmental and social impacts. A such plan will ensure a long-term perspective on natural resources management incorporating economic, environmental and social values. The plan can be revised and updated at regular intervals, and it will serve as guidance for public and private investors.

Licenses and permits need to be given with certain terms and conditions to mitigate impacts on the ecological and social environment. The terms and conditions need to be subject to oversight by the authorities, and there should be penalties for non-compliance to the terms.

To identify the impacts from hydropower, it is recommended to adapt a systematic approach following Environmental and Social Impact Assessment (ESIA) methods². ESIAs identify the valued environmental and social components, assesses the potential impacts of the project upon these, and suggests measures to mitigate the impacts, which can be used to set the terms of the license. It is important that there is an obligation to monitor and evaluate how the mitigation measures function, and their effectiveness, and eventually adapt the measures to better meet the objectives.

Some examples on how legislation is used to ensure mitigation measures are listed:

•

In Norway, where hydropower provides around 95 percent of all electricity, a Master plan for hydropower development was developed in the 1980's. The objective was to classify all water courses for either potential hydropower development or protection. The main criteria for classification were power plant economics and the degree of conflict in relation to different user interests (sport fishing, tourism, recreation, etc) and impacts on the environment (ecosystems and biodiversity). When a hydropower licence is given, special terms taking care of environmental mitigation measures are given. Old licences are being revised after 30 years (40 or 50 years in some cases), in order to update the terms according to current scientific knowledge. However, the terms and obligations are always balanced against the need for electricity and power. Each licence term is subject to a comprehensive consultation process before the Ministry for Oil and Energy make the final decision. If the terms are violated, a special department for environmental crime in the police are entitled to fine the hydropower operator.

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•

In Switzerland, where hydropower provides about 50 percent of all electricity generation and plays a major role for integration of other renewables, a special fund to be used for

mitigating negative impacts of hydropower is established. The fund is financed by an addition to the electricity bill to consumers.

•

In Sweden, hydropower watercourses and their hydropower plants are classified according to their capability of providing flexibility and regulation to the electricity grid. Power plants and watercourses that are important for the electricity grid flexibility are given less strict environmental mitigation measures. Hydropower companies in Sweden has also established a common fund to support mitigation measures where it is most needed, regardless who is the owner of the hydropower plant or the operator of the river regulation system.

•

The Norwegian Agency for Development Cooperation has supported Bhutan's Department of Energy to develop a GIS-based system and a database for hydropower projects, as well as a masterplan for developing their hydropower resources. The support also included

developing a licensing and tariffing system for the energy sector and establishing a legal system that separates the regulation and operation of hydropower plants.

•

The International Finance Corporation has developed a Strategic Environmental Assessment (SEA) of the Myanmar hydropower sector considering environmental and social values at the river basin level, recommending an approach to achieve sustainable hydropower

development. The SEA recommends moving the initial planning focus away from individual projects to basin health to plan a sustainable sector development.

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3.2 Mitigation hierarchy

A hydropower project should aim to minimize the ecosystem impacts, while optimizing the generation of energy. In order to ensure no-net-loss or net-gain of biodiversity¹⁵ as a result of the development of a hydropower project, the mitigation actions should follow the Mitigation Hierarchy¹ (Table 1), applied in the following order:

1) measures designed to avoid impacts 2) measures to minimize impacts

3) measures to mitigate and restore biodiversity

4) measures to compensate or offset residual biodiversity impacts if needed

Table 1 Common mitigation measures following the mitigation hierarchy, focusing on impacts on fish

Mitigation

hierarchy Possible measures

Avoidance

• Project siting (avoid main stem and sensitive ecosystems)

• Project design elements (Run-of-River to avoid large reservoir, reduced bypassed reach, necessary height of dam)

• In-water work timing (relative to migration and spawning)

• Flow regime (smooth variations in flow, peaking amplitude and timing)

• Regulating weir or dam to absorb peaking impacts

Minimization

• Fish passage (ladder, lift, nature-like, trap/truck, upstream, downstream)

• Sediment management (flushing schedule)

• Minimum water flow in diversion reach

• Guidance structures, racks and louvers for safe downstream fish migration

• Screens to prevent fish from turbine entrainment

• Fish-friendly turbines allowing fish to pass turbines with minimum damage

• Environmental Flow Requirements Restoration

and mitigation

• Enhance aquatic habitats in river and tributaries

• Address external pressures (overfishing, sediment/sand mining)

• Fish hatcheries and propagation for reintroduction

• Address cumulative impacts in the river basin Offsets and

enhancing habitats off- site

• Enhance aquatic habitat in sites outside the project influence or in another river or tributary

• Protected aquatic habitats

• Artificial fish propagation (for local consumption or supplement only)

Avoidance and minimization measures offer the greatest opportunity to reduce potential impacts of hydropower projects on rivers and can reduce the project’s liability for restoration and offset measures, which are often harder and costlier to achieve¹. “No net loss” and “net gain” can be delivered via restoration offsets, avoided loss offsets, or positive conservation actions¹⁵. The best opportunity to identify and apply mitigation measures for hydropower projects is at the earliest design stage of a project when siting of the project’s infrastructure is being considered^1,2.

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3.3 Mitigation measures and decision management

In management and decision-making, balancing different needs, costs and benefits are crucial and also a challenge. For hydropower projects, the benefits for the energy system are obvious. If the hydropower project can store water, the benefits are both in the form of renewable electricity production and as provider of flexibility to the electricity network. There may also be benefits in a higher degree of river regulation related to water management (i.e. flood control, drought management, domestic, irrigation or industrial water supply, navigation, etc.).

In terms of monetary values, the costs of mitigation measures are not possible to generalize as they must be adapted to site-specific conditions. However, there are some general trends, as well as some general cost data that can provide a basis for determining costs. When mitigation measures are planned as an integral part of the hydropower project development, it is generally less costly than imposing measures at a later stage or by retrofitting existing assets. Some costs related to standard elements like amount (m³) of concrete for fish ladders, number and dimensions (m²) of trash racks with a certain bar spacing or volume (m³) of gravel for creating spawning grounds are possible to generalize. However, how much of these quantities that are needed for each power plant and dam are site specific.

The costs of hydropower development and management are not only given in monetary value (e.g.

costs of construction or loss of income related to reduced fisheries in diverted rivers) but also related to the loss of biodiversity or reduced productivity and resilience in ecosystems which cannot easily be monetized, including loss or reduction in ecosystem services. These values must be weighed in addition to monetary values when defining and designing mitigation measures. It is also necessary to set the objectives of the measures with a targeted effectiveness in mind.

The effectiveness can be set for the functioning of the measure, for example in how large a

proportion of fish population that should be able to ascend a fish ladder or how large a proportion of artificial spawning grounds that should be used by fish each year. Alternatively, the effectiveness criteria could also be indicated at a high level as the number of fish species still breeding in a river section. The effectiveness of a measure can then be monitored for potential improvements.

Adjustments to the mitigation plan can be made accordingly, which is referred to as adaptive management. As it is often difficult to foresee the impacts of the hydropower project and the implemented mitigation measures, adaptive management is often required to obtain good and lasting solutions.

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4. Specific mitigation measures

Impacts related to hydropower and fish, as well as possible mitigation measures are categorised in many articles, guidelines, handbooks and tools. Some of the most relevant documents, reports and tools are listed under References^{2,9, 13}. In this report, the impacts and good practice mitigation measures are classified in five categories (Table 2).

Table 2. Main categories of hydropower impacts on fish and good practice mitigation measures to address them.

Flow and temperature regimes

Hydropower may change the magnitude, duration, timing, frequency, and rate of change in flow events. Good practice mitigation measures are release of water to river sections that have altered flow regimes or where water is diverted or bypassed, often called environmental flow, ecological flow or just e-flow.

Alterations and loss of habitats

Changes in flow regime and lack of dynamic geomorphological processes may lead to large changes, degradation and loss of habitats. Different structural mitigation measures like constructing riffles and pools, adding stones and gravel, adding large organic debris, combined with flow release are good practice mitigation measures.

Downstream fish migration past dams, weirs, and other infrastructure

Dams and weirs obstruct fish from moving downstream, and there is a risk of being entrained into the turbines of the hydropower plant. Trash racks to stop debris from entering the turbines often have bar openings wide enough for fish to pass through. Good practice mitigation measures are trash racks with finer spaced openings to exclude fish and different ways and constructions to guide and lead fish to a safe migration route over spillways or through gates.

Upstream fish migration past dams, weirs, and other infrastructure

Dams and weirs often block upstream fish movements. good practice mitigation is installation of step-pool or vertical slot fish ladders, nature-like fishways or other installations designed for the fish species in the river. It is also important to ensure that fish can find and enter the fishway, at least in the migratory season.

Declining fish populations

An overall impact of hydropower is often declining fish populations. To compensate for this or for lost habitat, stocking fish from hatcheries is common all over the world. It is possible to stock fish as eggs or very young individuals, but it is more common to stock them after some initial breeding at the hatchery. The chance of adapting to local conditions are higher when fish are stocked early or as eggs. It is important to ensure that stocking does not compromise the natural fish population or reduce the natural genetic variation.

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4.1 Flow regime and water temperature

Hydropower operation can change natural flows in downstream rivers and alter their magnitude, frequency, duration, timing, and rate of change which are recognized as the five key components needed to sustain biodiversity and ecosystem integrity^10-12. Water temperature may also be altered by hydropower design and operation. Flow and water temperature will be affected by changes in seasonal flow redistribution and transfer and diversion of water between catchments. Stream flow is the main driver of the physical condition of riverine ecosystem, and flow changes will have an impact on other factors since they are directly dependent on the availability of water.

If the hydropower production discharge will follow a changing load in the electricity system,

especially if there is a large proportion of intermittent energy sources such as wind and solar power, it may be characterized as a hydropeaking operating regime with peaking and off-peaking (low or zero) production. Both storage and Run-of-River hydropower can be operated with hydropeaking.

Storage hydropower will typically reduce the magnitude and frequency of floods, but it may also increase the duration of high flows. Because of its smaller storage volume size, Run-of-River hydropower has less ability to regulate the flow and will often have to produce power from the available reservoir inflow, i.e. limited alteration of the flow regime. However, daily peaking during the peak load hours is also possible from run-of-river hydropower.

Mitigation measures include the release of water to river sections that have an altered flow regime or where water is diverted or bypassed, often called environmental flow, ecological flow or just e- flow. The implementation of e-flows (operational measure) may require some technical measures and may be combined with structural measures:

• Operational measures: Measures considered in the hydropower operation planning and scheduling to ensure the e-flow release. These measures include imposing operation

constraints, operation objectives, and/or target flow regimes. The implication of imposing an e-flow on the discharge scheduling may include minimum flows through the year, as well as freshets and seasonal variations, among others.

• Technical measures: To ensure the release of e-flow, modifications should be made on the power plant infrastructure, e.g. a technical setup that allows release of water through gates, a wider range of turbine discharges, slower stop and start-up, among others.

• It is also possible to introduce structural or hydro-morphological measures carried out in the riverbed or in reservoirs, or structures connected to the river system, to reduce effects from low water levels, low water velocities and minimise hydropeaking effects (to be elaborated in following example and chapter 4.2 Habitat).

E-flows are often suggested as mitigation measure in the planning of hydropower projects through environmental and social impact assessments (ESIAs), or in licensing processes from the authorities.

There are also a large set of methods, reports, and guidelines for deciding e-flows^1,3. The key message is the intent to recreate the main components of the natural hydrological regime (floods, low flow periods, variation in flow). However, release of large amounts of e-flow outside the turbines may be challenging to combine with an economically sound project. A combination of structural and operational measures can often be a good alternative.

Direct monitoring of the effectiveness of the implemented e-flow regime to maintain the fish populations is seldom possible. However, overall studies of the fish population through different methods, e.g. electro-fishing, environmental DNA, at representative sites, may give a good indication about how well e-flows are helping to sustain fish populations.

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Good Practice:

INNERTKIRCHEN HYDROPEAKING, SWITZERLAND

Characteristics Innertkirchen I, Innertkirchen IE, Innertkirchen II

HPP type High head storage hydropower plant in a complex system of several storage and run-of-river power plants

Owner Kraftwerke Oberhasli (KWO)

Operation start date 1942

Installed capacity 255 MW

Expected generation/year 750 GWh/year

Turbines 5 Pelton turbines (Innertkirchen I) Flow rate through Powerhouse 39 m³/s

Operation of power plant

Peaking Load and Backup, powerhouse underground creating peaking problems downstream of the outlet. Use 672 m of difference in altitude to produce energy between the Handeck reservoir and the Aare River in Innertkirchen

Bypass reach 16 km

River flow information

Annual mean discharge in the hydropeaking section is ca. 35 m³/s. Natural minimal flow in winter is 2,4 m³/s (based on data from 913–1921). Floods from May to October (190 m³/s), occasional winter floods can reach 40 m³/s.

Fish migration species documented in river

Brown trout (Salmo trutta)*, bullhead (Cottus gobio), rainbow trout (Oncorhynchus mykiss), brook trout (Salvelinus fontinalis), arctic char (Salvelinus alpinus),

grayling (Thymallus thymallus), burbot (Lota lota), and perch (Perca fluviatilis).

The Hasliaare (also called Aare) is a gravel-bed river regulated by the hydropower company Kraftwerke Oberhasli (KWO) which has built nine powerhouses and several artificial reservoirs in the Hasliaare catchment. The major issues in the Hasliaare River are directly related to flood protection and hydropower production. The HPPs generated approximately 1 750 GWh in 2010, corresponding to 10% of the electricity produced by Swiss HPPs and covering the energy

consumption of approximately 1 million inhabitants. Two of the hydropower plants (Innertkirchen I, IE and II), operates with significant hydropeaking. To reduce the effects from hydropeaking, mitigation measures have been implemented according to Swiss legislation.

Mitigation measures

The cantonal and federal authorities have chosen to construct a 20 000 m³ retention basin (Figure 4) and a gallery in the mountain from the powerplant to the retention basin with a volume of 60 000 m³. This makes it possible to reduce the "flow falling rate" (also referred to as the "ramping rate" – up or down), which is expected to reduce stranding risk of juvenile fish at low flows.

Minimizing the flow up-ramping rate is expected to reduce macroinvertebrate drift.

Through a cost-effectiveness analyses, it was found that the 80 000 m³ volume was the most cost- effective since smaller volumes were not enough to mitigate the peaking effects and larger volume were resulting in disproportionally higher costs. The retention pond was completed in 2016. A monitoring program over the next 10 years was planned to evaluate the predicted ecological improvements, further optimize the regulation of the retention volume, and gain new knowledge on the efficiency of such mitigation measures. The first results have shown a significant increase in the number of juvenile fish.

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Good Practice:

INNERTKIRCHEN HYDROPEAKING, SWITZERLAND

Figure 4. Retention volume basin and gallery and its effects reducing hydropeaking Lessons learned

• Integrating modelling methods and using different indicators for physical and biological responses addressed the hydropeaking problem and supported hydropower plant owners, authorities, and water resource managers in planning, evaluating, selecting, and realizing appropriate and effective mitigation measures.

• Interdisciplinary collaboration among scientists and stakeholders was fundamental for creating a common understanding of river ecosystems affected by hydropeaking before developing a broadly accepted approach for effective evaluation and implementation of mitigation measures.

• This case study, including the future outcomes of the planned long-term monitoring, will provide useful information and necessary guidance for the evaluation of adverse hydropeaking impacts and possible mitigation measures. However, authors also stated that more research is needed, especially to establish a standardized and reliable relationship between measurable and predictable hydrological parameters, and the status class of ecological indicators.

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4.2 Habitat

The aquatic habitat is defined by the flow regime, the hydraulics and the morphology of the river or reservoir. The physical habitat determines the biotic composition and supports the productivity and sustainability of aquatic ecosystems⁸. Water velocities, turbulence and water depth change instantly as the flow changes. The composition of the substrate develops and changes at a slower rate, determined by sedimentation and erosion processes, mostly controlled by high flows and floods.

Hydropower operations will affect all these components of the habitat.

The hydropower dam creates a reservoir or a ponded river, that previously was a free-flowing river or a lake. If the created reservoir or ponded river was a free-flowing river before the dam was created, the environment is changing drastically. Species that prefer flowing waters (lotic species) will no longer find their natural environment. For lakes turned into reservoirs, the change in habitat conditions are manageable. However, ponded river reaches and reservoirs will see changes in water level according to hydropower operations and inflow. Seasonal filling and drawdown of the

reservoirs may influence the freshwater species in the reservoir.

Bypassed or diverted river reaches downstream of the dam will receive no flow from the turbines, and water must be released as e-flow through gates, special e-flow turbines or by other means. A certain minimum quantity of water is necessary to maintain aquatic life. In addition, it is possible to change the habitat conditions by structural measures such as creating appropriate substrate, suitable water depths and water velocities through alterations of the riverbed itself. To accommodate a much lower flow, it may also be necessary to narrow the river by creating a "river-in-the-river". This

concept is using a narrower part of the former river to construct nature-like sequences of habitat structures that are found in the river, typically riffles and pools with various substrate sizes (Figure 5) Habitat and substrate in river reaches downstream of the powerplant outlet will receive the same total amount of water as in natural conditions, but it may be distributed differently throughout the year, month, week, and day.

Riverbanks are often covered with embankments and flood protection measures, and they may be lacking riparian vegetation. This is normally not due to hydropower, but it must be considered together with planning mitigation measures.

Figure 5. A "River-in-the-river" at Øyvollen, Norway, where 85 % of the water is diverted through a powerplant. The "new"

river runs inside the old river channel as a narrower river channel with functioning riffle-pool sections, creating more suitable habitats for fish and invertebrates. Flood may still pass through the whole section. Photo: Knut Alfredsen.

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Good Practice:

HABITAT MITIGATION LAUDAL, NORWAY

Characteristics Laudal hydropower plant

HPP type Storage reservoir

Owner Agder Energi

Installed capacity 32 MW

Expected generation/year 146 GWh/year

Turbines 2 Francis turbines

Flow rate through Powerhouse 110 m³/s

There are six hydropower plants in the system with Laudal being the one most downstream. The powerhouse is

underground, with 36 meters of head and a 6 km tunnel. This Leaves a bypass section of the river with minimum flow until the powerhouse outlet (i.e., tailrace).

Bypass reach 6 km

River flow information Inter-annual discharge is 88 m³/s. Instream flow was 1.5 during winter and 3 m³/s during summer.

Fish migration species

documented in river Salmon, and sea trout have the highest interest.

The river Mandal River, located in southern Norway, is 115 km long with a catchment area of 1800 km² and a mean annual discharge of 88 m³ s. The river is regulated by 6 hydropower plants and 9 reservoirs. Nearly 90% of the storage capacity is found in the Nåvann and Juvatnet reservoirs in the surrounding mountains. Atlantic salmon can migrate 47 km upstream from the sea to a final migration barrier at the Kavfossen waterfall which includes the two lowest hydropower plants, Bjelland and Laudal. They were constructed in a period when Atlantic salmon were absent from the river due to acidification of the water. To mitigate the aesthetic effects of the low minimum flow and maintain a continuous water level in the bypasses of the hydropower plants, eight stone weirs and one low concrete weir were constructed in the late 1980's at the 6 km bypassed reach. It was argued that the combination of low flows and the weirs were negatively impacting the Atlantic salmon population that was back in the river after several years of liming program and stocking.

Mitigation measures

The Norwegian Water Resources and Energy Directorate (NVE) implemented a new minimum flow regime to double the amount of water that was previously being released into the bypass reach as a voluntary act of the hydropower company. This new regime included a release of 6 m³/s in winter, a spring release of 50% of the inflow during the smolt migration period, and 8 – 25 m³/s in summer, depending on inflow. To find an optimal release in which the hydropower company will not lose a significant amount of money from the release of water, a combination of hydro- morphological changes in combination with different releases were tested to find the most cost- effective solution. The hydro-morphological changes comprised the removal of several of the weirs in the bypassed reach, and the addition of spawning gravel (Figure 6). The simulation results were discussed with the hydropower company and it was decided to carry out this measure. In general, the present situation with the removal of the weirs, combined with increased water discharge and addition of spawning habitat has led to an improvement in habitat conditions and salmon production. More monitoring is still needed to confirm conclusive findings, but preliminary results show that the habitat mitigation measures implemented were successful.

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Good Practice:

HABITAT MITIGATION LAUDAL, NORWAY

Figure 6. Before (left) and after (right) weir removal in Mandal River. Upper figures (simulated results) lower figures after being removed.

Lessons learned

• It is possible to improve fish habitat and, therefore, fish production through the implementation of mitigation measures

• The use of previous modelling techniques allowed different mitigation alternatives and search for the most cost-effective option.

• Implementing hydro-morphological changes in the riverbed reduced the amount of e-flow needed to ensure habitat improvements in the bypassed river reach, and hence mad it possible to maintain a higher power production while still meeting environmental objectives.

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4.3 Upstream fish migration

Dams and weirs blocking the river will be a barrier for fish to move upstream. In addition, dams and weirs can also lead to fragmentation of habitats and disrupt the longitudinal connectivity. For instance, adult fish can be unable to reach regular spawning grounds located upstream of a barrier, inhibiting their natural lifecycle. Barriers to migration can have a large impact on fish in river sections far upstream if they stop natural migration patterns from the sea or from rivers and lakes in the downstream part of the catchment. Even if mitigation measures are installed to make barriers passable, barriers still have an impact on fish as their migration may be delayed.

Different fish passage facilities are implemented to mitigate the impact from barriers on migration and movements. Even with appropriate and good fish passage facilities, it is often time-demanding for individuals and fish schools to find the intended route. The path-seeking behaviour of fish implies increased energy consumption which may reduce survival. Comprehensive studies from the last decades indicate that most of the existing fishways have poor efficiency^4,5. The hydrological (flow rate, water level) and hydraulic conditions (velocities, turbulent features), might limit the utilization of fish passage facilities. Usually, the insufficient conditions (i.e. low flow rate, too low or too high velocities) originate from ambiguous design (e.g. improper location, too high a gradient, small pools, dysfunctional resting pools, etc.) and from the lack of maintenance, or the combination of both.

Fish migration does not necessarily happen year-around. For most fish species, they have a distinct migration period. During these events, when fish search the fishway or wait to pass, their upstream migration is delayed and may lead to increased mortality.

There are many types of fishways⁴. The most common are pool-type fish ladders for fish that are strong swimmers and able to jump, and vertical slot fish ladders for fish that swim close to the bottom. The pool-type fish ladder is easy to adapt to different locations, and it is the most commonly used. However, the vertical slot fish ladder has a wider suitability for different species even under changing flow conditions. Baffle-type fishways consist of a series of special deflectors on the floor and on the channel sides as well, applicable for use in steep terrain where space may be limited.

They create relatively strong flow conditions, which are suitable for large fish that are good

swimmers. Nature-like fishways look like small creeks or side channels to the main river that has a much lower slope to make it possible for fish to swim through. They require a larger footprint for construction and like all mitigation measures, they must be carefully designed to meet the

requirements of the local fish population. A challenge for all fishways, is to make sure fish can find the entrance, and to adapt the flow in the fishway to make it possible for fish to select entering the fishway. When the powerhouse is located at the foot of the dam, there may be a much stronger current coming from the turbines. When the powerhouse is located further downstream, the challenge is often to attract the migrating fish into the bypassed reach of river.

Alternatives to create a fishway, is to trap fish in a chamber or similar where it is possible to close the entrance. Fish can then be guided into locks just like ships, guided into a lift, being pumped upstream the dam or loaded on trucks for transporting them to upstream areas. Most of these solutions are quite costly and require advanced and specialised technical and operational procedures, as well as constant funding to ensure the functioning and maintenance of these measures.

All fishway structures need to be maintained to avoid blockage, clogging or reduced capacity, and it is important to monitor their efficiency. It is possible to do adjustments after construction or in design flow for most types of fishways if they are not working well.

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4.4 Downstream fish migration

When fish migrate downstream from reservoirs or ponded rivers from hydropower dams, they risk being drawn (entrained) into the power plant turbines. The passage through the turbine blades is dangerous as blade strikes and the increased pressure damage fish with small injuries (for juveniles, at low-head hydropower systems), to even lethal damages (increases with body length or at high- head hydropower systems). If there is a safe migration route, fish may have challenges in locating it.

This may lead to increased energy consumption and higher risk due to predation. In cases with long delays, species with synchronized migration can decide to turn back and not migrate in the season.

Floating guidance structures and trash racks are common installations in front of turbine intakes to stop debris from entering into the powerhouse. However, conventional trash racks have normally wide enough opening between bars to allow most fish to pass. There is a risk for impingement to large individuals which cannot pass through but may be forced towards the racks. Even though new design of fine trash racks is improving the capability to safeguarding fish downstream, these

solutions are not implemented many places and their performance need more evaluation.

There are many ways of guiding fish to avoid passing through the turbines while migrating

downstream. Operational measures include reducing or closing flow through turbines at the same time as flow is increased through alternative routes like spillways, gates, fishways and other installations. If the migratory season is short, this alternative may be possible. Often migratory season coincides with the monsoon/rainy season and there is a need for spilling water due to high inflow rates.

If there is a safe route for downstream migration, fish need to find the route and it is often important to guide the fish towards the safe route. Sensory and behavioural barriers created by electricity, light, sound or air-water currents (bubble curtains) may be effective if designed properly. More solid guidance structures like skimming walls and louvers or similar, can be effective. They are technically more difficult to construct, install and maintain and, therefore, potentially more costly.

For low-head turbines, there has lately been a focus on creating fish-friendly turbines. In contrast to ordinary turbines, fish-friendly turbines have low rotational speed, large diameter and small spaces between turbine blades and turbine housing.

It is also possible to construct the intake in a way that fish will not be entrained into the turbines. In bottom-type intakes (Tyrolean intakes, Coanda intakes), water passes over a horizontal or inclined rack where water to turbines is "filtered" vertically, and fish and debris are flushed further

downstream to the river.

Assessments of functioning and effectiveness of measures for downstream fish migration may be difficult, but targeted mark-recapture and telemetry studies will provide good data to assess most types of measures for downstream migration.

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Good Practice:

FISH MIGRATION AT LAS RIVES, FRANCE

Characteristics Las Rives

HPP type Run of the river

Owner Ondulia

Installed capacity 2.7 MW

Expected generation/year 3 Francis turbines 2 dive turbines

Turbines 45 m³/s

Flow rate through Powerhouse

There are 7 hydropower plants upstream and downstream of Las Rives, there is a water storage upstream of this water body, and hydropower upstream operate with hydropeaking which influence the Ariège’s flow, leaving it with a moderate hydrology.

550m

Bypass reach 6m

River flow information Mean annual discharge is 41.8 m³/s. Low-water flow is 12 m³/s, and the instream flow is 4.6 m³/s

Fish migration species

documented in river An alternate vertical slot pass is located at the dam. The flow in the fish pass is 0.5 m³/s.

Downstream migration: inclined bar rack associated to outlets

salmon, see trout, lamprey, eel, brown trout. The river is dominated by cyprinids and salmonids.

In the Ariege river in France, Las Rives hydropower plant was presenting a problem for both downstream and upstream migration issues with particular interest for the impact on Atlantic salmon. The hydropower plant was composed of three Francis turbines protected by a bar rack positioned in front of the hydropower plant. The mean bar spacing was 40 mm, but the rack was damaged and the effective bar spacing varied between 27 to 66 mm. The bar rack did not have a good efficiency to mitigate problems related to downstream migration. Indeed, the bar spacing was too big to represent a physical barrier to silver eels and was not very efficient for Atlantic salmon smolts. The efficiency stopping Atlantic salmon smolts to go through the turbines was estimated at 50-55%, and it was 20% for silver eels of 70 cm length. For upstream migration, the main problems were related to lower attraction flows than those needed to attract fish to enter the bypassed river reach between the dam and the powerhouse outlet, and pass efficiently through the fishway structure constructed at the dam.

Mitigation measures

In accordance with the environmental regulations for downstream protection and e-flows, in 2014, the hydropower operator undertook major works. The bar rack was replaced with a bar rack with a bar spacing of 20 mm with a 26° angle to the horizontal. It was placed at the head of the headrace channel instead of in front of the turbines. The operator also decided to install two more turbines, which will allow an increase in the attraction flow in the bypassed reach that only would cause a

³

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Good Practice:

FISH MIGRATION AT LAS RIVES, FRANCE

Different scenarios were tested to compare the cost-effectiveness of different flows releases, turbines composition and bar rack protections. The results indicated that the actual mitigation measures (Figure 7) were found to be most cost-effective measures. Fish tracking also confirmed with radio-tagged Atlantic salmon smolts and silver eels that the efficiency is around 81% for Atlantic salmon smolts and 100% for silver eels.

Figure 7. Layout of the current situation at Las Rives after implementation of mitigation measures

Lessons learned

• It is possible to improve downstream and upstream migration without compromising energy production.

• Installing new turbines that will increase the e-flow will at the same time increase the production of energy compared to pre-mitigation measures.

• Despite including higher head losses than the former design, the new bar racks are easier to clean, and they are having less head loss when the bar rack starts to become clogged.

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Good Practice:

FISH PASSAGE AT ENGENHEIRO SERGIO MOTTA DAM, BRAZIL

Characteristics Engenheiro Sergio Motta Dam, Brazil

HPP type Run-of-river

Owner Companhia Energética de São Paulo (CESP)

Installed capacity 1 540 MW

Expected generation/year 10.5 TWh/year

Turbines 14 Kaplan turbines

Height of dam 22m

Reservoir size 2 250 km²

River flow information Annual mean discharge at the dam is ca. 11 500 m³/s. In extremely rainy years the flow can reach 60 000 m³/s.

Fish species documented in the river

37 species from 17 families and 5 orders. Dominant families are: Characidae, Anostomidae, and Pimelodidae; while most dominant specie is: Rhinelepis aspera

Figure 8. NASA image of the Paraná River before (1987) and after the Engenheiro Sergio Motta dam has been built and put into operation (2000) (Source: Wikipedia Commons)

The Paraná River in Brazil is part of the catchment of the La Plata River in Argentina, which is the tenth longest river in the world and second longest river in South America, having a total length of 4 695 km. The 13 km wide Engenheiro Sergio Motta dam fragments the Paraná river with its 13 km wide and 22 m high structure (Figure 8). It was built from 1990 to 1999 and required two- stages to fill the 220 000ha reservoir upstream of the powerplant. The run-of-river powerplant is equipped with 14 Kaplan turbines and has chambers to install four additional units in the future.

Mitigation and monitoring measures

One 520 m long fish ladder has been built on the left bank of the river, which is near to the original layout of the river to facilitate fish migrating upstream and downstream over

approximately 20 m elevation difference. The entrance of the fishway to upstream migratory fish is located at the side of the powerhouse at an angle of 45°. The fishway consists of a sequence of 50 concrete weirs forming pools between them with 8 m intervals. In addition, each weir has six orifices (three at the upper end and three at the lower end), of which four can be controlled via metal plates (closed or open state) to alter the flow pattern in favor of fish movements. The pools are dimensioned to 5 m width and 2 m depth.

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Good Practice:

FISH PASSAGE AT ENGENHEIRO SERGIO MOTTA DAM, BRAZIL

Through two monitoring programmes from 2004 to 2005 researchers observed thousands of individuals from numerous species, families and orders inside the fish ladder. Samples were taken during a two-days period with eight-hour intervals monthly between December and March. The aim was to determine the number of individuals and species present at the fish ladder (Figure 9). In addition, the monitoring programme provided information on upstream and downstream movement of species.

Figure 9. The location of the fish ladder at the Engenheiro Sergio Motta Dam, Brazil (Source: Makrakis, et al., 2007)

Lessons learned

• Fish ladders can function with acceptable efficiency at large hydropower plants where the abundance of fish is high in numbers of individuals and species as well.

• Systemized monitoring at lower, middle, and upper sections of the fish ladder, even over short periods, provides valuable information on fish species utilizing the ladder and using it successfully for passage over approximately 20 m elevation difference.

• A single mitigation measure is potentially selective to fish species, which possibility increases consequently with the number of species. It is particularly the case, when fish species with different sizes, capabilities and swimming strategies are present.

• Pools with the weir and orifices are known as good solutions to species with great swimming capabilities. However, further interdisciplinary collaboration is necessary to assess the overall efficiency of the fish ladder for all target species. Moreover, population dynamics must be investigated on longer term up- and downstream of the dam as well, to evaluate the efficiency of the fish ladder and aim at good operation strategies of the ladder.

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Good Practice:

FISH PASSAGE AT UNKELMÛHLE, GERMANY

Characteristics Unkelmühle hydropower plant, Germany

HPP type Run-of-river

Owner Innogy SE

Operation start date 1920's (modern times)

Installed capacity 0.6 MW

Turbines 3 Francis turbines

Flow rate through Powerhouse Max. 27 m³/s

Reservoir length 2.3 km

River flow information Annual mean discharge at the confluence with the Rhine is ca. 53 m³/s.

Fish species documented in river

Numerous species are documented in the river Rhine, while target species for the presented study are Atlantic salmon smolts (Salmo salar) and European eel (Anguilla anguilla)

The Unkelmühle hydropower station (Figure 10) is installed on the Sieg River 44 km upstream from the confluence with the Rhine, in Germany. The first historical documentation of utilizing the power of the river at Unkelmühle is documented from the early 17^th century. In the 20^th century, a modern hydropower plant has been installed to the site to supply energy to nearby factories.

Today it is equipped with three Francis turbines with 27 m³/s of total capacity, which exploits 2,7 m elevation drop. The powerplant has been rebuilt in 2011 as part of a pilot project to restore longitudinal connectivity for fish species, particularly for downstream migratory juvenile Atlantic salmon (Salmo Salar) and silver eels (Anguilla Anguilla).

Mitigation and monitoring measures

The following measures have been implemented at Unkelmühle to aid the two-way passage of migratory species over the hydropower plant: 1) nature-like fishway with a discharge of 0.2 m³/s combined with a canoe pass with an additional 0.2 m³/s flow rate approximately 200 m upstream of the hydropower plant; 2) a spillway 100 m upstream of the hydropower plant; 3) turbine intakes equipped with horizontally sloped racks (inclination is 27º relative to the ground), with 10 mm bar gap, which are combined with bypass routes via flushing channels with discharge of 0,6 m³/s; 4) vertical slot fish passage located at the side of the hydropower plant with discharge of 0,3 m³/s;

5) custom-made bypasses located at the bottom, and 6) located at the side for downstream migratory eels. Additional alternative routes for downstream migrants are via the ice gate, located at the side of the powerhouse and over the dam crest during high-flow conditions, situated from the upstream entrance of the nature-like fishway.

A comprehensive monitoring programme was conducted on the site in 2014 and 2015 to capture and tag 270 eels and 256 smolts with radio transmitters in order to assess the route choice, delay and passage efficiency through the Unkelmühle power station

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Good Practice:

FISH PASSAGE AT UNKELMÛHLE, GERMANY

Lessons learned

• Rebuilt hydropower plant equipped with several mitigation measures can help safe passage over the barrier for target species in different size and with different swimming strategies

• Fine-spaced bar racks (10 mm) combined with alternative escape routes offer fish-friendly solutions to prevent passage over the turbine chambers. It is particularly effective on larger fish, like eels while safe alternatives are ensured.

• Custom-made bypasses for eels were barely used by them, while other alternatives were used by many eels. This finding shows the importance of combined solutions, as one custom-made measure might be less effective than others, initially made for different species.

• Despite careful planning and implementation of different mitigation measures smaller fish (smolts with 105 to 212 mm body length) can endure sever loss at regulated river sections for hydropower production (mortality is 16 - 25%; combined at the power house and in the reservoir section). Such mortality may not be detrimental for the fish population at the studied site depending on the state of the population, however it shall be discussed always at each site

Figure 10. The Unkelmühle power station from aerial view with the combination of fishways pass the power station (from T. Havn).

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4.5 Fish stocking to mitigate declining populations

Hydropower development may lead to declining fish populations for various reasons, and in many cases, there are expectations of reduced or extinct fish populations. For decades, stocking hatchery- reared fish has been used as a compensational measure to counteract reductions in fish populations, for conservation of endangered species or just to improve fisheries and increase harvest. In

hatcheries, brood stock is normally taken from the actual river and used for breeding eggs. Juvenile fish are often brought up to a suitable size before stocking them in the river or reservoir.

According to the mitigation hierarchy, stocking fish is the last option as it is mainly a compensational measure. A successful fish stocking program should be based on¹⁴:

• Developing and applying clear, specific, quantifiable harvest and conservation goals for natural and hatchery populations

• Designing and operating hatchery programs in a scientifically defensible manner

• Monitoring fish populations, evaluating the effectiveness, and adapting the hatchery programs accordingly

The traditional practice of replacing natural populations with hatchery fish to mitigate for habitat loss and mortality due to impacts from hydropower is no longer regarded as consistent with international good practice in conservation. Fish stocking must be seen in combination with other mitigation measures and managed without compromising natural fish populations in the catchment. Fish stocking and hatcheries may still play an important role in conservation of endangered species, and hatcheries will still be important for aquaculture and for nutrition and fisheries in some cases.

Figure 11. Fish rearing ponds at Kali Gandaki hatchery (photo: Atle Harby)