On quantifying ecologically sustainable flow releases in a diverted river reach

Water demand for hydropower production has been increasing along with a growing awareness of the importance of preserving riparian ecosystems and their biodiversity. Some Cantons in Switzerland have begun replacing the inadequate concept of Minimum Flow Requirement (MFR) with a dynamic one, by continuously releasing a percentage of the total inflow. In this work, we evaluate both ecological and economical benefits of dynamic release policies within a diverted river reach in the Swiss Canton of Graubunden. We compare such policies to another one that generates inflow-dependent variable releases as a result of an economic competition between traditional (e.g., hydropower) and non-traditional (e.g., environment) water uses (Perona et al., 2013). We propose to compute flow statistics from different release polices by using Indicators of Hydrologic Alteration (Richter et al., 1996; Richter et al., 1997). Then, we aggregate the hydrological differences from the natural flow regime as a proxy for assessing environmental benefits and we look at the mean of the ratio of the allocated net flows between environment and hydropower as a suitable engineering parameter to represent their relative value. Eventually all the simulated release policies find an economical significance explained by marginal utility functions. We show that dynamic redistribution policies can perform better than MFR-like ones. Moreover, by introducing the concept of inflow-dependent water allocation, both economic and ecological indicators can be further improved, without necessarily implying higher installation costs. This method aims to provide a simple but effective step towards eco-sustainability in the growing market of mini hydropower plants, where MFR-rules are still widespread. (C) 2013 Elsevier B.V. All rights reserved.

Optimal water allocation in small hydropower plants between traditional and non-traditional water users: merging theory and existing practices

Benoît Crouzy, Lorenzo Gorla, Paolo Perona

Water demand for hydropower production is increasing together with the consciousness of the importance of riparian ecosystems and biodiversity. Some Cantons in Switzerland and other alpine regions in Austria and in Süd Tiröl (Italy) started replacing the inadequate concept of Minimum Flow Requirement (MFR) with a dynamic one, by releasing a fix percentage of the total inflow (e.g. 25 %) to the environment. Starting from a model proposed by Perona et al. (2013) and the need of including the environment as an actual water user, we arrived to similar qualitative results, and better quantitative performances. In this paper we explore the space of non-proportional water repartition rules analysed by Gorla and Perona (2013), and we propose new ecological indicators which are directly derived from current ecologic evaluation practices (fish habitat modelling and hydrological alteration). We demonstrate that both MFR water redistribution policy and also proportional repartition rules can be improved using nothing but available information. Furthermore, all water redistribution policies can be described by the model proposed by Perona et al. (2013) in terms of the Principle of Equal Marginal Utility (PEMU) and a suitable class of nonlinear functions. This is particularly useful to highlights implicit assumptions and choosing best-compromise solutions, providing analytical reasons explaining why efficiency cannot be attained by classic repartition rules. Each water repartition policy underlies an ecosystem monetization and a political choice always has to be taken. We explicit the value of the ecosystem health underlying each policy by means of the PEMU under a few assumptions, and discuss how the theoretic efficient redistribution law obtained by our approach is feasible and doesn't imply high costs or advanced management tools. For small run-of-river power plants, this methodology answers the question "how much water should be left to the river?" and is therefore a simple but effective step towards eco-sustainability. References - Perona, P., Characklis, G., Dürrenmatt, D.J., 2013. Inverse parameters estimation of simple riparian benefit economical models. Journal of Environmental Management . - Gorla, L. and Perona, P., 2013. On quantifying ecologically sustainable flow releases in a diverted river reach. Journal of Hydrology.

2014

Frontiers of (Pareto) Optimal and Sustainable Water Management for Hydropower and Ecology

David Andrew Barry, Amin Niayifar, Paolo Perona, Pierre Razurel

River regulation alters the natural flow regime of streams with consequent impacts on terrestrial and aquatic habitats of the riparian zone. The severity of such impacts can be modulated by changing the redistribution rules at water intakes and reservoirs. Contrary to minimal-flow policies, non-proportional and proportional redistribution policies result in variable environmental flow releases, namely Dynamic Environmental Flows (DEFs), which improve the global (i.e., ecological and economic) efficiency of water use practice, e.g., for energy production. DEF assessment is based on different indicators. However, the choice and aggregation method of different hydrological and fish habitat indicators affects the assessment of the global power plant performance, i.e., the Frontier of efficient solutions (sensu Pareto). This study investigates DEF assessment, and shows the extent to which the choice and method of aggregation of different indicators impacts the Frontier of Pareto-efficient solutions. The findings are supported by six case studies of hydropower practice that differ in terms of river morphology, energy production amount and technique. The relative importance of several types of indicators is examined as is their influence on optimal and sustainable water allocation solutions that lie on the Pareto Frontier. The analysis shows that DEFs arising from either proportional or non-proportional redistribution rules can positively impact strategies of sustainable management of freshwater resources.

2021

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.