A report from engineering firm Poyry takes a look at how the hydropower industry is taking responsibility for environmental conservation in the 21st century, and what steps need to be taken in the future.
Across the world, rivers are used intensively to support human activities. One consequence of this intensive use can be the reduction of open passages, essential for the migration of aquatic species. Owners and contractors of hydropower facilities, in particular, are under public and ethical pressure to maintain the ecological soundness of impacted areas. In many countries, mitigation measures have become a legal requirement. But is enough being done to ensure the design of hydropower projects provide truly sustainable solutions - not simply complying, but gaining acceptance from all stakeholders?
This report will review the focus areas for habitat conservation and improvement, and detail mitigation measures being adopted in the industry, before outlining the crucial steps the industry must take to ensure sustainable operations that meet expected standards internationally..
Where do conservation issues arise in hydropower development and how can they be mitigated?
Habitat conservation and improvement for fish and other aquatic life are crucial for the whole riverine ecosystem. Understanding the specific behaviour of local species is the starting point in order to address the unique needs for each and every project.
There are three important focus areas that can impact fish and riverine life which must be considered among others: migration, ecoflow and hydropeaking. These considerations are outlined in the following paragraphs with modern mitigation measures being adopted by the industry.
Dams and weirs in rivers introduce a barrier for many species. Thus keeping water passages sufficiently open for migration (with the use of appropriate facilities) is crucial for the survival of populations and a fundamental hydropower design element.
Mitigation measures include:
- Upstream migration: Ladders, passes, ramps, locks, elevators and deviation channels can be used to ensure safe passage upstream.
- Downstream migration: Barriers, grids, bypasses and fish friendly equipment help ensure safe passage downstream.
A river's natural balance needs to be maintained if it is to continue fulfilling its required functions following the manipulation of a river flow. Numerous rivers dry up periodically as a result of water withdrawals at 'intake' sites (i.e. for irrigation, drinking water, hydropower). The residual flow (or 'ecoflow') remaining in a watercourse downstream of an intake must be sufficient to preserve the various functions served by rivers, such as the provision of habitats for wildlife, feeding aquifers, or breaking down pollutants.
Mitigation measures include:
- Minimum legal requirements: The often required constant flow release can be ensured by appropriate gate and outlet operation.
- Regulated flow release: According to specific ecological requirements dynamic regulation controlled by monitoring facilities improves downstream flow quality.
- Ecoflow turbines: Turbines releasing water directly downstream of the dam or weir allow enough water in the impacted river in addition to energy production.
When 'peak load' energy occurs at a hydro plant, it can result in unsteady water releases to rivers, altering the natural flow regime. This can diminish the biomass and richness of species, including fish at several life stages. Mitigating the adverse impacts on the aquatic ecosystems is a mandatory requirement in today's water policies as well as being best practice.
Mitigation measures include:
- Operational measures: The operation schedule of a plant can be modified for specific ecological requirements. This should be achieved without major production losses.
- Construction measures: A compensation basin or cavern downstream of turbine release, a powerhouse outflow deviation or morphological improvements of the riverbed are technical measures to cope with hydropeaking without impacting plant operation.
Challenges relating to habitat conservation and restoration
After decades of intensive use of water resources, governments and other organisations have started to implement water protection policies through legal frameworks such as the European Union Water Framework Directive.
This has had a mobilising effect on parts of the industry. Extensive experience has been gained and many schemes are being transformed in order to meet stringent environmental requirements. Existing facilities are being 'rehabilitated' for habitat improvement or restoration and new facilities designed with a focus on habitat conservation.
However, internationally, there are regions still suffering from a lack of experience in respect to hydropower-related ecological challenges and little scientific knowledge available on local ecosystems. Even if the type of design constraints are similar to common projects in developed areas, their magnitude is often much higher. Key constraints for fish migration facilities design in undeveloped areas include:
- Large biodiversity (a far wider range of migrating fish species than in developed areas).
- Large biomass rate (several tons of fish per hour during migration peak).
- Managing 'ecoflow' (implications of ecoflow turbines with relatively high discharge and high head).
- Deviation in water levels river flow during the year.
A five step approach to sustainable development
The report has provided an overview of the three core sustainability considerations: migration, ecoflow and hydropeaking, and explored ways in which to mitigate impact during the design and operation of hydropower projects. Introduced now is a five step approach for sustainability in hydropower that is well-known, but not always well applied.
The five steps cover the lifespan of a hydropower project including habitat conservation aspects. To begin with it is essential to have monitoring and data acquisition in place at the pre-build stage to ensure the 'default' wildlife behavior and balance is logged. This will then inform pre-build decision making that will involve drawing comparisons and commissioning the build to realise the most appropriate design. Finally, there must be ongoing performance review and adjustment based on effects caused through operations. This is an ongoing activity and the process repeats during the lifespan of the hydropower project.
Local knowledge, global experience
Every HPP is unique so best practice is not to apply the same design, but to apply the same guiding principles. For example, Pöyry's approach is a proven scientific-technical method based on evidence, research and experience gained in tropical and temperate regions.
By developing in-house expertise and partnering with external specialists, Pöyry has provided innovative technical solutions to mitigate adverse impacts on aquatic biota. Best practice principles learnt from wide experiences combined with the collection of expert knowledge and specific in-situ information allows Pöyry to continue to push state-of-the-art facilities to new levels.
Hydropower decreases dependency on fossil fuel of the countries where it is installed, has a positive impact on local employment and allows balancing of other renewable energy sources. It is so far the cheapest way to store energy. Hydropower technology is mature and therefore plants have a very long and predictable lifetime, with minimal operation and maintenance costs. These are the reasons why hydropower should see its capacity doubling to 2000GW by 2050, according to the IEA.
However, if not designed correctly, it can have catastrophic effects. That's why it needs to be done on a sound scientific basis and for reasons not just of complying to requirements but gaining acceptance from all key stakeholders - from investors to local communities.
In order to do so, the industry has a good foundation with a theoretical approach to sustainability, but one that isn't always observed or fulfilled correctly.
For this reason, genuine practical expertise, informed by international experience, is necessary to balance sustainability and deliver projects on time and within budget. ¦
Xayaburi HPP, Mekong, Lao PDR
Hydropower is the favoured energy generation option for the Mekong's riparian countries. Laos has an ambition to become the 'battery of Southeast Asia'. Pöyry is acting as the Government of Lao Engineer for the construction phase of the 1300 MW Xayaburi HPP.
Pöyry advised the contractor to completely revise the original tender design of the fish migration facilities and has taken an active part in the new concept design development in close collaboration with specialist fisheries consultants and the contractor.
Pöyry also co-ordinated the on-site 'physical capability and behavioural' tests on indigenous fish species. This enables design decisions to be based on local scientific data. Several different migration facilities with individual adjustment potential will considerably reduce the ecological impact of the project.
"We worked closely with Pöyry, the Owner's Engineer of Xayaburi project, to develop a fish pass design, optimised to maximise efficiency for fish migration across a very diverse assemblage of fish species, while also functioning within the operational constraints of the site," says Dr Toby Coe, Technical Director, Fishtek Consulting, UK. "The design used best practice international fish pass criteria, however, to ensure that the hydraulic parameters were relevant to Mekong species, additional investigations on the local fish were conducted in order to develop a more specific design for the fish pass. Our recommendations for the fish passage facilities from a more general stand-point were supported by Pöyry, while their experience in engineering and large hydropower projects complemented our own experience in fisheries biology and fish pass design, construction and monitoring."
Wyhlen HPP, Rhine, Switzerland
The High-Rhine, the river section upstream of Basel on the border between Switzerland and Germany, has been an important spawning ground for salmonids. Fish habitat deterioration caused by 11 existing HPPs has required regeneration. Longitudinal connectivity of suitable water passages is crucial to reinstate fish access to such locations.
In close collaboration with fish ecologists, Pöyry redesigned the 90-year-old fish pass of the Whylen HPP. As the plant had to remain fully operational during the whole construction period, innovative techniques were developed. The result is an ecologically sound and cost-effective mitigation measure.
Melk HPP, Danube, Austria
The Danube, one of the world's largest and most diverse river basins, is a central infrastructure connection for Europe. In accordance with the economic prosperity in the area, the ecological integrity of the Danube should be reestablished.
Pöyry provided development and design services to the first fish migration corridor for an existing HPP on the Danube in Austria. The 2km long diversion channel of 12m height difference is equipped with an inlet weir structure, a vertical slot pass as well as ordinary and emergency dynamic flow release systems.
Since 2007, the ecological effectiveness of the innovative concept has been monitored and approved.