Méthodologie pour la conception et la gestion des aménagements hydrauliques à buts multiples par une analyse systémique

Repeated failures as well as difficulties related to the implementation of new hydroelectric powerplants in industrialized countries illustrate the paradigm evolution which manages relationship between human society and nature. Problems resulting from these plants, often ignored during planning phases, in addition to the current trend to restore a natural state, require ecological analyses for new constructions as well as for scheme restoration or river corrections. Taking into account energy and ecology, together with security, financial and socio-economical aspects, transforms the design of hydraulic schemes into complex problems. Designing, dimensioning and managing in an integrated way such multipurpose hydraulic schemes thus require new approaches. The first objective of the present work is the comprehension of the complex system formed by a multipurpose hydraulic scheme and the determination of its most important characteristics. The second objective aims at developing a methodology to quantify the installation impacts on the key factors of the system. The third objective is an optimization of the system itself as well as the determination of the distribution of the cost between the various purposes. The developed methodology first includes a qualitative analysis of the system which then allows a quantitative modelling. Optimization is carried out on the basis of this second modelling. The cost distribution is finally obtained by comparison of partial optimizations of the system. The qualitative analysis is carried out starting from the method developed by Gomez and Probst (1995) which is based on a cognitive representation in order to model the complex system behavior. This representation includes feedback loops between the various factors. The mathematical analysis of the network classifies these factors and highlights the most important ones (key factors). In the particular case of the multipurpose run-of-river hydroelectric scheme, this method distinguishes the decisional level from the functional level. It underlines the variable, namely the downstream flow, which constitutes the bond between the two levels. The purposes of this project are to reduce hydropeaking, to produce energy, to offer a retention volume for flood mitigation and to allow a social use for leisure activities. Quantitative modelling is carried out by simulation models, considering an optimized operation of the reservoir which determines the downstream flow. This optimization is performed by a mathematical resolution using the software AMPL. It includes the constraints to reduce the downstream flow variations with the objective of maximizing energy production. It also results in minimal reservoir water level variations. The simulation models then calculate the scheme behaviors (hydraulic, energy, thermal, ecological, social and financial). The flood management is treated separately, with the objective of reducing the flood peak by preventive draining of the reservoir. A financial comparison of the probable impact of retention on peak floods is carried out by evaluating the potential of lowering downstream dams. An optimization of the turbine dimensioning, specifically applicable in case of highly variable water levels (upstream and downstream) and flow discharge, is also developed. The general optimization of the system, performed with the optimization tool QMOO (developed at the Industrial Energy Systems Laboratory – EPFL), is related to variables which determine the size of the scheme. This optimization is carried out in two stages. The first stage determines, for each goal of the system (partial optimization), the optimum production conditions of the set goal. This stage defines a transfer function between the optimal production and the minimal investment. The second stage determines, by a complete optimization using the transfer functions, the set of optimal solutions. These optimal solutions are then filtered by two successive filters : the synergistic filter eliminates solutions which do not reduce the investment, whereas the filter of the actors eliminates solutions which produce quantities below the limit or which require investment above the fixed limit. The complete methodology, developed in 12 steps from the qualitative analysis to the final set of solutions, is applied to a study case on the Swiss Upper Rhone River. The solutions found are able to satisfy the requirements of the various actors while generating a saving on investment higher than 10 %. This reduction, called synergistic profit, is compared to the sum of the optimal investments of a single purpose scheme carried out separately. The solutions found require an investment in the range of 150 to 180 MioCHF. They allow producing 42GWh/yr of electricity, reducing the current hydropeaking by approximately 30% and offering a social impact calculated at 55'000 visits per year. The available volume for flood management oscillates between 5 and 8 Mio m3. This research work, carried out within a team of ecologists, architects, civil and mechanical engineers, producers of hydroelectricity and public authorities, showed the relevance of the selected approach which led to the feasibility of the suggested solutions. In addition, the modularity of the developed methods (qualitative analysis, hydropeaking management, probabilistic retention impact on flood peaks, optimisation of turbine dimensioning, partial and complete optimizations) allow a wide range of possibilities for partial use, for applications to other works or for future developments. The principal results of this research can be defined as follows : 1) an operation method is developed in order to absorb more than 50% of the current hydropeaking while losing less than 10% of the energy potential, 2) the financial retention impact on flood peak is justified, 3) turbine dimensions are optimized in case of strong variability on both flow and head, 4) conception and dimension of multipurpose schemes are performed in an integrated way and lead to solutions which allow cost saving for each objective.

Optimization of low-head hydropower recovery in water supply networks

Irene Almeida Samora

Small scale hydropower is emerging as a decentralized source to satisfy local demand for electricity. The interest in micro-hydropower, which refers to installed power below 100 kW, is increasing since this is a solution with low environmental impact. Water supply systems are one of the main manmade water systems presenting potential for micro-hydropower. Although some applications already exist in adduction lines, the urban distribution networks remain unexplored. Because these are complex systems in which flows and pressure vary constantly, specific technology and installation schemes for energy recovery are lacking. This work accesses the potential for hydropower within water supply networks (WSN) and presents an arrangement of micro-turbines specially conceived for this type of installation. The arrangement is based on a novel inline turbine suitable for pressurized systems and its best location within the networks is studied. The five blade tubular propeller (5BTP), preliminarily designed in the framework of the European Project HYLOW, was further developed and tested in this work. An experimental campaign was conducted with a large range of heads and torque measurements to access its characteristic curves and to obtain hill charts. The relative positioning of the turbine-generator shaft regarding the pipe bend was modified from a downstream position to an upstream position. Efficiencies of around 60% were found. The adequate locations in WSN for micro-hydropower plants are identified using an optimization algorithm which considers both the assessment of the energy production and sizing of the main equipment and works. A concept for the implementation of the 5BTP in the field was developed, consisting of an arrangement with up to four turbines inline within a buried chamber created around an existing pipe. Two objective functions, energy production and economic value respectively, are used. A simulated annealing process is developed to optimize the location of a given number of turbines. This procedure takes into account the hourly variation of flows throughout an average year and its effect on the turbine efficiency. The optimization is achieved by considering the characteristic and efficiency curves of a turbine with different impeller diameters and simulating the annual energy production in a coupled hydraulic model. After a convergence analysis for different restrictions and numbers of installed turbines, the algorithm was applied to analyze the feasibility of the proposed arrangement in two case studies in Switzerland: a sub-grid of the city of Lausanne and the complete WSN of the city of Fribourg. In both cases, the implementation of the proposed energy recovery solution seems to be feasible. A detailed analysis of the cost breakdown revealed that the cost of additional pipe work, which are required in each layout to guarantee a by-pass supply in case of maintenance, may have an important role on the investments. Also, the pressure reduction valves locations, if they exist, are likely to be the optimal solutions. Finally, a methodology to quantify the potential for hydropower based on the excess energy in a WSN is proposed and applied to case studies. It allowed to conclude how much the proposed arrangement can extract from the networksâ energy potential. In addition, an attempt was made to produce an expedite method to estimate the energy produced with one 5BTP based on network parameters and dimensional analysis.

EPFL2016

Ecological response of a multi-purpose river development project using macro-invertebrates richness and fish habitat value

Marc Pellaud

It has been acknowledged that river morphology and hydrology have been intensively altered due to the anthropic demands in floodplain land use and management, flood protection, promotion of navigability or energy production. Rivers were transformed in water highways, having lost contact with their surrounding floodplain as well as the plethora of ecological processes and occupants once thriving in these ecotonal zones. The identification of this emerging threat of morphological and hydrological alteration on ecological integrity adds further complexity in the exploitation of hydrosystem resources. These resources are heavily coveted and guarded by different lobbies each having strategic views on future project development. Stakeholders may want to promote hydro-electricity, ecologists a natural reserve, communes may wish to have an increased flood protection and leisure promoters a nautical center. As a result, the proposition of a river development project is certain to face opposition of one party or the other. The motivations of this dissertation are anchored in this context, where various and sometimes conflicting potentials for hydrosystem exploitation remain. This works aims at contributing scientifically to an innovative approach at the conception phase of a multi-purpose river development project by developing the ecological module to be implemented in the general project's optimizer. The SYNERGIE project hypothesis is that it should be possible to identify a synergetic pattern joining the interests of ecological integrity, flood safety, energy production and leisure development. Such a multi-objective river development project would stand more chance of acceptance. This dissertation focuses on the ecological aspects of such a river development project and an application on the regulated Swiss Upper Rhone River. Is expected an ecological answer to a river development project design / management which has to be compatible with Heller's Heller (2007) general SYNERGIE project optimizer taking into account all the project poles. The system of interest is composed of a buffering reservoir of ca. 1 km2, a run-of-the-river dam, a hydro power-plant, and an artificial river ensuring longitudinal continuum. The primary part of the work consisted in an extensive literature review on system understanding, anthropic alterations and quality assessment / prediction tool available. The approach consisted of two levels (1) the general ecological considerations to be followed at the project reservoir scale and (2) the measure of the downstream ecological response through modeling. General ecological considerations at the reservoir scale were the implementation of an artificial river ensuring longitudinal connectivity, implementation of artificial ecotonal boosters and the allocation of a sanctuary zone with limited public access. The downstream measure of ecological integrity was based on the choice of three taxonomic groups of macro-invertebrates and four ecological guilds (groups) of fish. Mayflies (Ephemeroptera), stoneflies (Plecoptera) and caddisflies (Trichoptera) richness were predicted using simple hydrological and morphological covariates (i.e. substrate, current speed,...) coupled to system specific faunistic surveys. Bank, riffle, pool and midstream fish guilds habitat values were determined using existing methods. By using the simulation results of river development project scenarios as inputs, the ecological response (i.e. the measure of ecological integrity) was computed following the assumptions that high predicted macro-invertebrate richness and high guilds habitat values were linked to a high ecological integrity. An emphasis on the hydropeaking effect in relation with river morphology was performed on macro-invertebrates. They were found to respond well to hydrological and morphological changes induced by river development projects while the approach by fish habitat value encountered limitations in its applicability. Four multi-objective project scenarios were analyzed, (1) the actual state of the Swiss Upper Rhone River at the Riddes site (VS), (2) a hypothetical hydropeaking mitigation project, (3) a hypothetical bed widening project and (4) a hypothetical bed widening coupled to hydropeakaing mitigation project. The actual state resulted in the worst measure of ecological integrity, with comparable results for hydropeaking mitigation project or the bed widening project. The highest measure of ecological integrity was observed for the coupling of hydropeaking mitigation and bed widening. These results showed that a multi-purpose project can increase the ecological integrity of the Swiss Upper Rhone River, produce electricity, provide protection from floods and develop local leisure activities. The synergetic effect of the project could be measured by project acceptance. Nevertheless, our knowledge on the hydropeaking effect on hydrosystem should still be completed by more research in order to give more weight to the ecological implication of hydropeaking.

EPFL2007

Operation of Complex Hydropower Schemes and its Impact on the Flow Regime in the Downstream River System under Changing Scenarios

Martin Peter Bieri

Hydropower is the world’s most important renewable electricity source. More than 40% of European hydroelectric energy is produced in Alpine countries. High-head storage hydropower plants (HPP) contribute significantly to peak energy production as well as electricity grid regulation. Future plant management is faced with several challenges concerning modified availability of water resources due to climate change as well as new economic constraints associated with legal, political and electricity market issues. HPP operation results in unsteady water release to the downstream river system. Hydropeaking is the primary factor of flow regime alteration, impacting the river ecosystem. Even when the biological response to hydropeaking is not fully understood, the recently adapted law on water protection prescribes its mitigation in Switzerland. In this research project, a novel integrative approach to model and assess the impact of the operation of a complex hydropower scheme on the downstream river system is developed. It contains (1) a precipitation-runoff model extended for long-term simulations of glacierized Alpine catchment areas, (2) an operation tool for high-head storage HPP, (3) flow regime generation with cost estimation of hydropeaking mitigation measures and (4) a habitat model of reference river morphologies for a target species. The upper Aare River (Hasliaare) in Switzerland is an Alpine stream, affected by hydropeaking from a complex hydropower scheme with several storage volumes and power houses. Since the 1930s, seasonal water transfer from summer to winter and the amplitude and frequency of daily peak discharge have been continuously increased. Furthermore, the dynamic braided river network with various mesohabitats gave way to a mainly monotonous channel. Although diversity of species and biomass of aquatic biota have drastically decreased, the potential of redevelopment remains. Investigations to improve the river morphology and the flow regime are under discussion. The upper Aare River catchment is therefore an appropriate case study for analysis of the interactions between climatic, hydrological, hydraulic, economic as well as ecological parameters. The simulation of runoff in Alpine catchment areas is essential for optimal hydropower exploitation under normal flow conditions, but also for the analysis of flood events. The semi-distributed conceptual modeling approach Routing System contains a reservoir-based precipitation-runoff transformation model (GSM-SOCONT), extended by dynamic glacier simulation tool. Spatial precipitation and temperature distributions are taken into account for simulating the relevant hydrological processes, such as glacier melt, snowpack constitution and melt, soil infiltration and runoff. The model development, calibration and validation are illustrated for the 2005 flood event, where the flood reduction capacity of the HPP is discussed, as well as future long-term runoff estimations. Climate change scenarios, based on a reference climate period, take into account intra-annual temperature and precipitation variations as well as their long-term tendencies. Runoff series of daily resolution are produced by hourly updating of the meteorological, glaciological and hydrological parameters. An almost complete deglacierization of the upper Aare River basin is simulated for the late 21st century. The resulting reduction of glacier melt in summer and earlier snowmelt in spring change the runoff regime from glacio-nival to nival. The implemented heuristic hydropower modeling tool in Routing System allows simulation of the operating mode of complex HPP. Within the case study of the upper Aare River catchment and despite the complexity of the HPP network, the influence of climate change, electricity market issues, plant enhancements as well as hydropeaking constraints is simulated and assessed. Despite the reduction of future runoff, increased flexibility due to new turbine and pumped-storage capacities allows compensation, especially in the case of volatile electricity prices, and could even partially restore the natural flow regime. Several operational and construction measures to reduce hydropeaking are implemented in the model. Resulting flow regimes as well as the related costs are defined. Operational constraints, such as limitation of turbine discharge, increase of residual flow or limited drawdown range, generate relatively high costs compared to their environmental effectiveness. Better ecological and economic response is achieved by construction measures, such as flow deviation systems or compensation basins installed downstream of the power house outflow where the water is temporarily stored and then released to the river by a guided system. The simulated flow regimes are rated by a river specific habitat model for representative morphologies and three life stages of the target species brown trout (Salmo trutta fario). This is based on results from a 2D hydrodynamic model and in situ investigations undertaken in the framework of a joint project of EAWAG. Steady and dynamic indicators quantify fish habitat suitability and allow comparison through economic indices of the implemented mitigation measures. For the Hasliaare River, investments for mitigation of hydropeaking are only justified by morphological improvements. The developed approach is useful for the enhancement of complex storage hydropower schemes regarding mitigation of altered flow regimes. Despite several uncertainties, it allows operators, authorities and researchers to define and rate the impact of HPP operation on the river network, to ecologically and economically assess mitigation measures and thus to address hydropeaking in a straightforward manner.

EPFL2012