Hydrological and hydraulic solutions for the sustainability of habitat life in human altered streams

Amin Niayifar
EPFL, 2019
Thèse EPFL

Résumé

In this thesis, I aim to contribute to the research towards improving the sustainability of habitat life in streams affected by anthropogenic activities. With the growing trend of altering natural water regimes due to hydropower operations, irrigation, and wastewater treatment plants, for instance, it is vital to minimize environmental effects. Here, I aim to address issues regarding human-altered streams that have received less attention in the community. In particular, I intend to provide solutions to improve the water management in the reservoir systems as well as investigating the role of macroroughness elements on the ecosystem functioning. For the water management part, the aim is to improve the global efficiency of storage systems, with the main focus being on the environmental aspect. Minimum flow releases nowadays are widely used to reduce the environmental effects associated with streams affected by anthropogenic activities. However, these static flow release rules have been found to markedly affect the stream ecosystem, mainly by reducing biodiversity. Aiming to reduce the environmental impacts caused by reservoirs, I propose a Direct Policy Search (DPS) framework based on defining dynamic flow release rules. I employ the mathematical form of the Fermi-Dirac statistical distribution to formulate dynamic non-proportional redistribution rules that partition the flow for energy production and environmental use. The energy production is calculated from technical data and the environmental indicator associated with flow releases by integrating the Weighted Usable Area (WUA) for fishes with Richterâs hydrological indicators. State-of-the art multiobjective evolutionary algorithms are used to find optimal flow release policies that have efficient economic and environmental efficiency. The results show that non-proportional flow releases can substantially improve global efficiency, specifically the ecological one, of the hydropower system when compared to minimal flow releases. This is mainly due to better water management of flood events that enables flow releases that mimic natural flow variability. In the part of my Thesis on streambed macroroughness, I investigate the contribution of macroroughness elements to stream ecosystem functioning, which generally is not considered due to their relatively small scale, using both modeling and fieldwork approaches. Macroroughness elements contribute to stream ecosystem functioning mainly by providing shelter zones for fishes as well as enhancing reach scale gas exchange. I develop an environmental indicator based on the aforementioned benefits of macroroughness elements on stream ecosystem functioning. Environmental indicators help define improved water management strategies by better characterizing the environmental impacts associated with human altered flow regimes. I define a physically based analytical model to estimate the size of wake areas downstream of macroroughness elements and make use of the derived distribution approach to calculate the statistical distribution of wake areas. To validate the concept, the model is applied to four exemplary streams having different statistical diameter size distributions of macroroughness elements. Furthermore, the proposed environmental indicator is included in the DPS framework to solve a multiobjective reservoir optimization problem. Next, empirical evidence is provided for the effects of macroroughness elements on stream ecosystem function

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https://infoscience.epfl.ch/record/271533?ln=fr

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Amin Niayifar
EPFL, 2019
Thèse EPFL

Résumé

Official source

https://infoscience.epfl.ch/record/271533?ln=fr

À propos de ce résultat

Concepts associés (37)

Concepts associés

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Publications associées (76)

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Ecohydrological Footprints

Samir Suweis

Ecohydrological footprints are defined as the response of ecosystem functions or services to changes in their hydrologic drivers. In this thesis, several diverse footprints are addressed: noise-driven effects on storage-discharge relations and catchment streamflow distributions, that are important drivers of biodiversity; soil salinization and its ecohydrological implications; topological effects of the ecological interaction networks on living communities (e.g. on their species persistence); and form and function of the global virtual water trade network. The coherence of the conceptual framework is provided by the study of drivers and controls of ecohydrological variability using methodological approaches based on statistical mechanics. In fact, this thesis work outlines a significant portion of environmental statistical mechanics, an overarching discipline that is emerging in recent years, which applies mathematical tools from statistical mechanics to model several ecohydrological processes. The proposed relevance of this thesis lies in the major effects of hydrologic drivers on ecological process. The view that emerges from current research in ecohydrology, that this thesis supports, is that there exists a definite need for an integrated understanding of ecological and hydrological processes. Because stochasticity is intrinsic to environmental and ecohydrological variability, noise plays an important and constructive role in ecohydrological processes. In this thesis, a stochastic approach is applied to analyze different ecohydrological processes, ranging from green and blue water flows in river basins (part I), ecosystem dynamics affected by the directional dispersal provided by river networks (part II) to water footprints of human society (part III).Methods range from novel exact solutions to stochastic differential equations to random graph theory applications, and imply the analysis of suitable field data. An analytical framework for quantitative analysis is laid out to tackle complex problems and to estimate the effects of environmental change on the interaction of the hydrologic processes with the biota. The main results of this thesis are: i) the achievement of exact solutions for the probability distribution of catchment streamflow, that takes in account stochastic fluctuations in the storage-discharge relation and for the condition of a noise induced phenomena to the streamflows regimes; ii) the stationary solutions of soil salinity under stochastic hydrologic forcing; iii) a novel solution of the Ito-Stratonovich problem in multiplicative Poisson processes; iv) the proper framework for species' persistence time distributions, as a function of topological constraints on the ecosystem, and its connection with other important macroecological laws. A related length-bias sampling problem is also solved. v) A statistical analysis of the global virtual trade network and a semi-analytical model that is able to describe most of the observed properties.

EPFL2011

Chargement

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

Chargement

Operation of complex hydropower schemes and its impact on the flow regime in the downstream river system under changing scenarios

Martin Peter Bieri

EPFL - LCH2012

Chargement

Ecohydrological Footprints

Samir Suweis

EPFL2011

Operation of complex hydropower schemes and its impact on the flow regime in the downstream river system under changing scenarios

Martin Peter Bieri

EPFL - LCH2012

EPFL2012