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In order to meet the growing demand for energy, the development of hydropower leads to an increase of the river exploitation by human activities. Thereby, water management has become a major issue in the energy transition. A better definition of the flow release rules is now required to improve the Minimal Flow Requirement (MFR) concept, which has long been used in spite of its environmental inconsistency. In this work, we present a class of non-proportional redistribution rules that broadens the spectrum of dynamic flow releases based on proportional redistribution for run-of-the-river power plants. We adapt the mathematical form of the Fermi-Dirac statistical distribution to engineer a novel class of redistribution functions. In particular, such functions are used to define the fraction of water allocated to the environment depending on the inflow at the intake. The theoretical background as well as the economic interpretation is presented, and the ability to generate variable flow releases carefully discussed. MFR, proportional and non-proportional distribution policies are then applied to a real case study and their respective economic and environmental efficiencies quantitatively compared. We show that non-proportional distribution policies allow for operating conditions actually close to the Pareto frontier, which improve both efficiencies with respect to those obtained from some traditional MFR and proportional policies. [ABSTRACT FROM AUTHOR]

Water exploitation for energy production from Small Hydropower Plant (SHP) is increasing despite human pressure on freshwater already being very intense in several countries. Preserving natural rivers thus requires deeper understanding of the global (i.e., ecological and economic) efficiency of flow-diversion practice. In this work, we show that the global efficiency of SHP river intakes can be improved by non-proportional flow-redistribution policies. This innovative dynamic water allocation defines the fraction of water released to the river as a nonlinear function of river runoff. Three swiss SHP case studies are considered to systematically test the global performance of such policies, under both present and future hydroclimatic regimes. The environmental efficiency is plotted versus the economic efficiency showing that efficient solutions align along a (Pareto) frontier, which is entirely formed by non-proportional policies. On the contrary, other commonly used distribution policies generally lie below the Pareto frontier. This confirms the existence of better policies based on non-proportional redistribution, which should be considered in relation to implementation and operational costs. Our results recommend abandoning static (e.g., constant-minimal-flow) policies in favour of non-proportional dynamic ones towards a more sustainable use of the water resource, also considering changing hydroclimatic scenarios. [ABSTRACT FROM AUTHOR]