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Adaptation options for hydropower plants

Hydropower generation depends, by definition, on the availability of water and is therefore affected by the impacts of climate change on water basins, mainly through two (opposite) pathways. Climate change can result in water scarcity, leading to lower river flows and lower accumulation of water into dams, and hence to a lower amount of water that can pass through turbines or run-of the river plants to generate electricity. Conversely, climate change can increase the frequency and intensity of extreme precipitation events and accelerate snowmelt, leading to increased flood risk. Some locations across the EU will be more prone to water scarcity issues and others to sudden abundance of water: typically droughts are expected to be a serious threat in most regions except northern Europe, and what are now once-in-a-century floods will be more frequent in all major European river basins (EEA, 2016). However, both phenomena can occur all over Europe, with changing frequencies in a changing climate.

This variability of expected hydro-meteorological changes across Europe is the rationale for the first adaptation option discussed here. In a climate change adaptation perspective, it is crucial for utilities operating hydropower plants to get a detailed understanding of the future conditions in which each plant will operate. Climate change will result in seasonal variation of the water circle, with longer dry spells during which water will be scarcer than usual, earlier thawing of snow on the mountain slopes in springs and hence earlier occurrence of large inflows of melting water as well as accelerated melting of glaciers that will result in an initial increase in water availability followed by a worsening of water availability. In absence of upstream flow-controlling infrastructures, early and more abundant spring flows can be problematic for run-of-the-river plants, by causing a mismatch between electricity generation and demand.

All these phenomena will require a thorough revision in the planning of hydropower plants’ operation, maintenance and possibly climate-proofing engineering interventions. Moreover, accurate scenarios will be key in order to find shared solutions for competing uses during periods of water scarcity, by helping gauge the actual needs and the likely timing of the demands by the various users beside electric utilities: farmers, fisheries, residential use, water transport, recreation, etc. Thus, a first adaptation option is setting up high resolution climatic and hydro-meteorological scenarios for each dam site and for the river basin they belong to, in a way that they can be easily accessed and understood by the electric utilities’ management and by all other users within the basin. To this purpose, specific climate services can be designed to provide accurate projections of the relevant indicators in an accessible format.

In some instances, projected climate conditions may suggest that a revision of planned activities may not be enough and that infrastructural adaptation may be in order. This is particularly the case when an increased occurrence of extreme precipitation events is expected, resulting in an increased occurrence of flooding at dam sites. Adverse effects of dam flooding include overtopping, outages, damage to equipment and adverse downstream impacts. The sudden abundance of water due to flooding needs to be discharged safely in order to minimise damages to the plant and to the downstream ecosystems and human infrastructures and activities. Extreme precipitation events can also trigger hydro-meteorological impacts such as landslides or excessive silting, which can reduce the volume available for water within a reservoir and/or clog the water discharge system.

There are a number of engineering options that can be applied to manage dam spills, which can be basically grouped into spillways, gated systems and fuse plugs.

Spillways can have various design shapes aimed at dissipating safely the energy of the discharged water while ensuring the desired outflow volumes. They may work automatically when the water in the dam reaches a given level or can be coupled with gates that divert the water flow into the spillway. Design shapes include chute spillways, stepped spillways, bell-mouth spillways, syphon spillways, ogee crests, side channels, labyrinth spillways and piano-key weirs (PKW). The technical features of a dam and of the orography and hydrology of the surrounding area determine the compatibility of specific spillway types with the dam: this implies that not all spillway systems are compatible with all dams.

Gated systems are a series of gates installed along the dam wall or around bell mouth spillways that can be opened to manage the reservoir’s water level and in particular to release downstream excess water volume in case of flooding. Again, they may be coupled with spillways to safely dissipate the kinetic energy of the discharged water. They are in place in many existing dams for flow management. Gated systems can fail in cases of saturation due to excessive flooding.

Fuse plugs are erodible sections of an earth dam which are designed to wash out in predetermined flooding conditions. Basically they act as buffers that absorb and slow down the overflow and can be sacrificed because the cost of rebuilding them is just a small fraction of the costs that would have to be sustained if the main dam was damaged. They can be installed only in presence of suitable geographic and geological features of the site and of compatible downstream conditions (e.g. a saddle at a reasonable distance from the main dam along the rim of the reservoir to discharge excess water; a solid rock foundation for the plug in order to withstand erosion; a channel to safely divert the overflow from the plug to the main river in order to protect downstream structures).

Usually, installation of spillways and gate systems can take place only during the dam construction phase, thus retrofitting is generally not an option. This does not apply to fuse plugs and PKW systems. A Climate-ADAPT case study on flood risk management for French hydropower plants discusses the pros and cons of PKWs. PKWs have some clear advantages compared to traditional spillways and gated systems, such as the feasibility of installation as retrofits within existing dams and well as the fact that they provide a free flow spillway without being constrained by maximum capacity limits, thus being able to cope with high flow levels and working in safer conditions than gated systems, and in a completely automatic way that does not require human intervention.

An extreme infrastructural adaptation option is the expansion of plant capacity by building larger dams. This may make sense in particular circumstances where a large increase in water runoff is expected to occur in the near future and long enough to allow recovering the investment costs. This can be the case when the meltdown of large glaciers is expected, as in a case study from Iceland. However, the applicability of this option to the EU is probably very limited due to the very different hydro-meteorological and glaciological conditions.

Additional Details
Reference information

Adaptation Details

Category

Grey

Soft

IPCC categories

Social: Informational, Structural and physical: Engineering and built environment options, Structural and physical: Technological options

Stakeholder participation

For climate services, what matters is the involvement of relevant potential users in the co-design process of the services. Thus it depends on how the service is intended: if it is seen as a planning tool for strict hydropower generation purposes, stakeholder involvement may not be a major factor. If however, a broader perspective is adopted and the service is designed to serve all the relevant users of the river basin, the co-designing process will lead to an interaction among representatives of all relevant user categories. Of course, the actual revision of planned activities in the light of the expected climate change impacts will then need to be as inclusive as possible to successfully minimize future conflicts.

Building new infrastructures, particularly the dam enlargements, requires the involvement of all river basin users and that an agreement is reached among them about water use rights and compensations.

Success and Limiting Factors

The advantages of providing clear and ready-to-use indicators for water use planning are quite self-evident, as efficient planning can be based only on accurate and well understood information. The main issue here is common to all climate services; it has to do with the difficulty intrinsic in, on one hand, identifying the state-of-the-art scientific information actually relevant for the users’ activities, and, on the other hand, packaging such information in such a way that the format and the language used to present it, are non-technical and accessible enough for users not familiar with the scientific disciplines applied. To this purpose the co-design stage is crucial.

Infrastructural adaptation is in most cases limited by the fact that most spillway and gate systems can be built only together with the dam, and hence are a valid option only for future hydropower projects. The main exception is the PKW system, whose flexibility and relatively low costs have been discussed in a related French case study, together with its (reportedly minor) limitations.

Costs and Benefits

Climate services for hydropower are generally quite inexpensive compared to infrastructural investments. In some instances, relevant data can be retrieved from projects not directly undertaken by the utilities operating the plants, for instance from research projects at the EU level which may provide (almost) free access for all relevant EU users. Consulting firms can provide more tailored packages at market rates, but the price range of such contracts can be expected to be within tens to hundred thousand Euros. Benefits from climate services boil down to minimizing future risk exposure and conflict with other water users, and optimizing the power generation profile in view of the expected changes in water availability profiles.

Retrofit installation of infrastructures to control excess water flow can cost from several hundred thousand Euro (200,000 for PKW, as reported in the French case study) to several million Euro depending on the specific characteristics of the dam, in terms of location, structure and water flow. The primary benefits are clearly the reduction of expected damages to the hydropower plant infrastructure and to downstream infrastructures and ecosystems, but also an increased ability to manage water levels within the reservoir; hence, retrofitting may bring about a smoother operation of the plant, which can increase profitability. When the installation of such infrastructures leads to higher average water volumes stored within the reservoir, this might result in higher electricity production if market conditions allow it, but also in an increased role for the reservoir as a buffer that can improve the resilience of the whole river basin.

The only potentially relevant legal aspects are those related to the authorization process for new infrastructures, such as new water discharge infrastructures occupying previously pristine portions of the river basin, and of course the construction of larger dams. These projects are subject to the national regulations for permitting of new infrastructures.

Implementation Time

Some climate services also relevant for hydropower plants planning and management are already available within Copernicus. Ad-hoc consultancy contracts by intermediaries can provide relevant climatic indicators in few months. For flood control infrastructures, construction times depend on the specific features of the dam and can vary between few months and few years. A few years are required to build larger dams.

Life Time

The lifetime of climate services is contingent on constantly updating and maintaining the user interfaces, databases and models. For infrastructural retrofits, there is no clear indication, but if properly maintained it can be assumed that they will last as long as the residual lifetime of the dam (usually several decades). Fuse plugs are by design supposed to be washed away at major flooding events, and their periodical reconstruction should be considered in the planning of the hydropower infrastructure they belong to. New dams’ lifetime expectation is on average 50 years, but they can last for up to a century, albeit with increasing maintenance costs and structural stability risks after 50 years.

Reference information

References:

Gimbergson, L. Full technical report: Hydro-power production in a future climate. Copernicus Climate Change Service.

World Bank and Water Partnership Programme (2015). Water & climate adaptation plan for the Sava river basin. Annex 3 – Guidance note on adaptation to climate change for hydropower.

Khatsuria, R.M., (2004). Hydraulics of spillways and energy dissipaters. Civil and Environmental Engineering.

Published in Climate-ADAPT Mar 23 2020   -   Last Modified in Climate-ADAPT Mar 23 2021

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