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

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.

On quantifying ecologically sustainable flow releases in a diverted river reach

Lorenzo Gorla, Paolo Perona

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.

Elsevier Science Bv2013

Influence of dam operation on water resources management under different scenarios in the Zambezi River Basin considering environmental objectives and hydropower

Théodora Cohen Liechti

The hydropower potential in Africa is only very few exploited. The large rivers like Zambezi River still have considerable possibilities for installing further hydropower projects including the creation of reservoirs by large dams. The main African watersheds comprise also very vulnerable biotopes as wetlands, floodplains and deltas. This is exactly the case for the Zambezi river basin with its precious Barotse, Lukanga and Kafue flats as well as its large delta region. The question is how operation of the existing hydropower plants and reservoirs would have to be adapted in order to ensure environmental flows able to maintain the essential functionalities of the biotopes. Furthermore new projects should be designed in a way to mitigate as much as possible the negative effects or even to improve the present state. With her research project Mrs Dr. Théodora Cohen-Liechti was confronted with this challenge. In order to give an answer to the mentioned questions, she had to develop a hydraulic-hydrological model in a very a large river basin under data scarcity, which was never done in such a detailed degree before, namely for a daily time step. Furthermore the model comprises all relevant hydraulic structures and schemes as well as vulnerable floodplains. For the latter a new sub-model based on a reservoir approach was specifically developed. Mrs Cohen-Liechti studied by the help of the hydrological model numerous scenarios combining different levels of environmental requirements as well as several future hydropower developments. The analysis showed in principal that a reasonable compromise between energy production and environmental sustainability could be reached. Finally with the comprehensive hydraulic-hydrological model of the Zambezi River including new planned hydropower projects as well as extensions of existing power plants, the impact of climate change on the energy production was analyzed.

EPFL - LCH2013

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

Influence of dam operation on water resources management under different scenarios in the Zambezi River Basin considering environmental objectives and hydropower

Théodora Cohen Liechti

EPFL - LCH2013