Albayrak, Ismail

Boes, Robert M.

Felix, David

Schmocker, Lukas

English

Hydraulic Engineering Repository

Article, Published VersionAlbayrak, Ismail; Felix, David; Schmocker, Lukas; Boes, Robert M.Research projects on reservoir sedimentation andsediment routing at vaw, ETH Zurich, SwitzerlandHydrolinkVerfügbar unter/Available at: https://hdl.handle.net/20.500.11970/109427Vorgeschlagene Zitierweise/Suggested citation:Albayrak, Ismail; Felix, David; Schmocker, Lukas; Boes, Robert M. (2018): Research projectson reservoir sedimentation and sediment routing at vaw, ETH Zurich, Switzerland. In:Hydrolink 2018/4. Madrid: International Association for Hydro-Environment Engineering andResearch (IAHR). S. 105-107. https://iahr.oss-accelerate.aliyuncs.com/library/HydroLink/HydroLink2018_04_Reservoir_Sedimentation_2.pdf.Standardnutzungsbedingungen/Terms of Use:Die Dokumente in HENRY stehen unter der Creative Commons Lizenz CC BY 4.0, sofern keine abweichendenNutzungsbedingungen getroffen wurden. Damit ist sowohl die kommerzielle Nutzung als auch das Teilen, dieWeiterbearbeitung und Speicherung erlaubt. Das Verwenden und das Bearbeiten stehen unter der Bedingung derNamensnennung. Im Einzelfall kann eine restriktivere Lizenz gelten; dann gelten abweichend von den obigenNutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.Documents in HENRY are made available under the Creative Commons License CC BY 4.0, if no other license isapplicable. Under CC BY 4.0 commercial use and sharing, remixing, transforming, and building upon the materialof the work is permitted. In some cases a different, more restrictive license may apply; if applicable the terms ofthe restrictive license will be binding.105hydrolink number 4/2018IAHRIntroductionHydropower is the most important source ofrenewable energy in Switzerland and consti-tutes the backbone of the Swiss electricitygeneration portfolio. Many reservoirs arelocated in the periglacial environment, i.e. incatchment areas of which at least 30 % isglacierized[1]. Climate change and theenvisaged transition to a more sustainableenergy supply system according to the ‘SwissEnergy Strategy 2050’ will challenge theexisting infrastructure. The retreat of manyglaciers in Switzerland may have significantimpacts on water resources, but it may alsoprovide opportunities such as new sites forhydropower reservoirs. New natural proglaciallakes have recently started to form at thetermini of a number of retreating glaciers in theSwiss Alps. These reservoirs partly formnaturally at rock rims after glacier retreat, yetsome need a man-made dam to ensure theirlong-term stability. However, the sediment yield and dischargedownstream of retreating glaciers tend toincrease, resulting in higher reservoir sedimen-tation. For sustainable reservoir operations, it isimperative to consider reservoir sedimentationand to plan and implement effective counter-measures. A number of field, laboratory as wellas numerical research projects at VAW of ETHZurich deal with reservoir sedimentation andassociated countermeasures. They are brieflydescribed hereafter.Hydropower Potential and ReservoirSedimentation in the PeriglacialEnvironment Under Climate ChangeThe goal of this project was to better under-stand the effects of climate change onreservoir sedimentation and hydropower devel-opment in the Swiss periglacial environment.The study was divided into three parts, namelya systematic investigation of the hydropowerpotential in Swiss periglacial catchments, afield investigation of sediment fluxes into andinside periglacial reservoirs, and the numericalinvestigation of long-term sedimentationprocesses and patterns in such reservoirs.In the first part, a framework based on anevaluation matrix with 16 economical, environ-RESEARCH PROJECTS ON RESERVOIR SEDIMENTATION AND SEDIMENT ROUTING AT VAW, ETH ZURICH, SWITZERLANDBY ISMAIL ALBAYRAK, DAVID FELIX, LUKAS SCHMOCKER AND ROBERT M. BOESReservoir sedimentation is a global concern and is expected to aggravate in the near future due to climate changeand the linked increase in sediment availability below retreating glaciers. There is an increasing need for efficientsediment management to maintain the active storage volumes in reservoirs and to improve the continuity ofsediment transport along rivers from upstream to downstream of dams. The Laboratory of Hydraulics, Hydrologyand Glaciology (VAW) of ETH Zurich, Switzerland, has conducted several basic and applied research projects onreservoir sedimentation and possible countermeasures (e.g. sediment bypass tunnels and increased fine sedimenttransport through power waterways).Figure 1. Griessee Reservoir with retreating glacier in the background, leading to higher sediment yield. (Photograph: D. Ehrbar, VAW, ETH Zurich)106 hydrolink number 4/2018water sample analysis, laser in-situ scatteringand transmissometry (LISST) and AcousticDoppler Current Profiler (ADCP) was applied inthe field measurements. In the last part, a 1-Dnumerical model was implemented using thesoftware BASEMENT[4] to simulate both thedelta formation of coarse sediments and thelake-wide sedimentation from non-stratified(homopycnal) flows. The model was validatedwith data from the Gebidem Reservoir and thenapplied to a potential future periglacialreservoir[2,3]. Based on the project findings,implications on future reservoir operations,considering climate change, werediscussed[2,3].Hydroabrasion in high speed flow atsediment bypass tunnelsSediment bypass tunnels (SBTs) are aneffective routing technique to reduce reservoirsedimentation, diverting sediment-laden flowaround the dam, thus allowing the re-estab-lishment of the natural sediment continuityalong the river (Figure 2a). Moreover, SBTsenhance the operating safety of dams byincreasing the outflow capacity, which is notsufficient anymore at many schemes[5,6,7].Despite these advantages, no guideline for thedesign and operation of SBTs is available andmany SBTs face severe invert abrasion due tohigh-speed sediment-laden flows, putting SBToperation at risk and causing high mainte-nance costs (Figure 2b). To address theseproblems, four research projects have beenconducted at VAW. The first project focused onflow characteristics, particle motion, particleand invert material properties, which aregoverning parameters of hydro-abrasion[6,8,9,10]. The study was conducted in aFroude-scaled laboratory flume modeling thephysical processes present in a straightsection of SBTs. The findings contributed to abetter understanding of the physical processesunderpinning hydro-abrasion of SBTs, and ledto the modification of an abrasion predictionmodel[10]. A second and complementary in-situinvestigation was conducted at three SwissSBTs[7]. Various invert materials were testedand the obtained data were used to calibratethe above-mentioned abrasion model.Furthermore, the field data contributed toimprove and optimize the bypass design and reservoir operations for better bypassefficiency [7]. The findings of both studies led toinitiate the third and on-going research projectentitled “Hydro-abrasion at hydraulic structuresand steep bedrock rivers”[11]. The focus of thisproject is to investigate the effects of lowaspect ratios of channel width to water depthand of sediment hardness and shape onsediment transport and hydro-abrasion in alaboratory flume, mimicking SBTs and high-gradient mountain streams. The fourth projectdealt with the morphological effects of SBToperation on downstream river reaches bymeans of a field study at the Solis SBT in theCanton of Grisons, Switzerland, and bysystematic numerical modelling of the SBTsediment pulses and their downstream effectsin terms of both bed slope development andmental and social criteria for consistent ratingof all potential Swiss sites was developed andapplied[2,3]. These criteria include the long-termrun-off evolution, natural hazards, sedimentcontinuity, protected areas, the visibility of newdams from populated places and effects ontourism. Seven suitable reservoir sites for newpotential hydropower plants (HPPs) wereretained, which are estimated to add 1.1 TWhof electricity per year[3]. With these new reser-voirs, the intermediate goal of the Swiss EnergyStrategy for hydro-electricity in 2035, i.e. 37.4TWh/a, can be met. The infill time of all sevenreservoir is 500 years or more, although ithighly depends on the future retreat of glaciers.In the second part of the project, suspendedsediment concentration (SSC), particle sizedistribution, bathymetry and flow velocity wereinvestigated in the three Swiss periglacial reser-voirs Griessee (Fig. 1), Gebidem and Lac deMauvoisin with infill times between roughly 30and 1000 years, to better understand sedimen-tation processes and delta formation[3]. Allthree reservoirs suffers from sedimentationproblem and countermeasures are needed fortheir sustainable operation. A combination ofFigure 2. (a)Schematic view of an in-streamreservoir withsedimentbypassing[7] and(b) abradedconcrete invert ofthe Runcahez SBT,Switzerland(Photograph: M.Müller-Hagmann,VAW, ETH Zurich)Figure 3. Increasing suspended sediment concentration (SSC) in turbine water as a countermeasure toreservoir sedimentation 107hydrolink number 4/2018IAHRbed material composition[12]. The outputs ofthese projects contribute to establish a generalguideline for sustainable and efficient designand operation of SBTs and other hydraulic/civilstructures exposed to hydro-abrasion[5,13].Reduction of reservoir sedimentationby increasing fine sedimenttransport through turbinesSediment flushing through dam bottom outletswith water level drawdown is a technique tomanage sedimentation problems in smallreservoirs. However, this is rarely feasible forlarge reservoirs due to important water losses.In addition, environmental regulations may limitthe admissible suspended sediment concen-tration (SSC) downstream of dams, or requestthat sediment transport is not hindered signifi-cantly by dams. An option to reduce sedimen-tation in HPP reservoirs in compliance withsuch environmental requirements is toincrease the transport of fine sedimentsthrough power waterways – and hence theturbines – to the downstream river reach[14](Figure 3). This has the advantages that (i) theSSC downstream of dams and powerhouses islow compared to those during occasionalreservoir flushing operations, and (ii) noflushing water is lost for electricity generation.The disadvantage of this option is that turbinesare exposed to higher sediment loads whichmay intensify hydro-abrasive wear. Turbinewear can be mitigated by appropriate turbinedesign and coatings as well as by limiting theSSC and particle sizes in the turbine water. The topic of turbine erosion and its negativeeffects (e.g. reduced turbine efficiency,production losses, increased maintenancecosts) have been investigated since 2012 inthe scope of an interdisciplinary researchproject at the high-head HPP Fieschertal in theSwiss periglacial environment. Varioustechniques for monitoring of suspendedsediment load, turbine erosion and efficiencychanges were tested and further developed[15,16]. Based on the acquired data, ananalytical erosion model[17] was adapted andcalibrated for coated Pelton buckets[15]. Thismodel can be used to estimate acceptableSSCs and particle sizes for the option ofincreasing the fine sediment transport throughpower waterways and turbines. By this way, thenegative effects of reservoir sedimentation andturbine erosion can be balanced in order tomaximize the profitability and maintain theoperational flexibility of storage hydropowerschemes. The sediment load in the power waterway maybe increased by hydraulic dredging (pumping)of previously settled fine sediment in thevicinity of the turbine water intakes (Figure 3).The flow rate in the dredging pipe is regulatedin such a way that the SSC in the turbine wateris acceptably low. The particle size may belimited by the suitable selection of dredgingarea (sufficiently distant from the reservoirinflow), as well as by screens or settling tankson the dredging boat.AcknowledgementsThe authors acknowledge the Swiss NationalScience Foundation (SNSF), Swiss FederalOffice of Energy (SFOE), swisselectricresearch, Swiss Committee on Dams,Gommer kraftwerke AG, Axpo Hydro SurselvaAG, Officine Idroelettriche della Maggia SA(OFIMA), Electra-Massa AG, Alpiq, HYDROExploitation SA, and equipment manufacturersfor their financial and/or technical supports inall mentioned projects. We also acknowledgeHochschule Luzern and Technical University ofDresden, Germany, for their collaborations. Allprojects are embedded in the framework of theSwiss Competence Centre of Energy Research– Supply of Electricity (SCCER-SoE), aninitiative funded by the Swiss Confederationthrough Innosuisse. nReferences[1] Hallet, B., Hunter, L., Bogen, J. (1996). Rates of erosion andsediment evacuation by glaciers: A review of field data and theirimplications. Global and Planetary Change 12(1-4): 213-235.[2] Ehrbar, D. (2018). Hydropower Potential and ReservoirSedimentation in the Periglacial Environment Under ClimateChange, Doctoral Dissertation, VAW-Mitteilungen 247 (R. Boes,ed.), ETH Zurich, Switzerland. https://doi.org/10.3929/ethz-b-000301149.[3] Ehrbar, D., Schmocker, L., Vetsch, D.F., Boes, R.M. (2018).Hydropower potential in the periglacial environment ofSwitzerland under climate change. Sustainability 10(8), 2794;https://doi.org/10.3390/su10082794.[4] Vetsch, D.F., Siviglia, A., Caponi, F., Ehrbar, D., Facchini, M.,Gerke, E.; Kammerer, S., Koch, A., Peter, S., Vonwiller, L. (2017).BASEMENT Version 2.7; ETH Zurich: Zurich, Switzerland.Available online:http://people.ee.ethz.ch/~basement/baseweb/download/documentation/BMdoc-Reference-Manual-v2-7.pdf.[5] Auel, C., Boes, R.M. (2011). Sediment bypass tunnel design -review and outlook. Proc. ICOLD Symposium “Dams underchanging challanges” (A. J. Schleiss & R. M. Boes, eds.), 79thAnnual Meeting, Lucerne, Switzerland: 403-412.[6] Auel, C. (2014). Flow characteristics, particle motion and invertabrasion in sediment bypass tunnels, Doctoral Dissertation, VAWMitteilungen 229 (R. Boes, ed.), ETH Zurich, Switzerland.https://doi.org/10.3929/ethz-a-010243883.[7] Müller-Hagmann, M. (2017). Hydroabrasion in high-speed flowsat sediment bypass tunnels, Doctoral Dissertation, VAW-Mitteilungen 239 (R. Boes, ed.), ETH Zurich, Switzerland.https://doi.org/10.3929/ethz-b-000273498.[8] Auel, C., Albayrak, I., Boes, R.M. (2014). Turbulence character-istics in supercritical open channel flows: Effects of Froudenumber and aspect ratio. Journal of Hydraulic Engineering140(4), 04014004.[9] Auel, C., Albayrak, I., Sumi, T., Boes, R.M. (2017). Sedimenttransport in high-speed flows over a fixed bed: 1. Particledynamics. Earth Surface Processes and Landforms, 42(9): 1365-1383.[10] Auel, C., Albayrak, I., Sumi, T., Boes, R.M. (2017). Sedimenttransport in high-speed flows over a fixed bed: 2. Particleimpacts and abrasion prediction. Earth Surface Processes andLandforms, 42(9): 1384-1396.[11] Demiral, D., Albayrak, I., Boes, R.M. (on-going). Hydro-abrasionat hydraulic structures and steep bedrock rivers. PhD project.http://www.vaw.ethz.ch/en/research/hydraulic-engineering/hydroabrasion-and-sediment-monitoring.html#abrasion.[12] Facchini, M. (2017). Downstream morphological effects ofsediment bypass tunnels, Doctoral Dissertation, VAW-Mitteilungen 243 (R. Boes, ed.), ETH Zurich, Switzerland.https://doi.org/10.3929/ethz-b-000225127.[13] Boes, R.M. Ed. (2015). Proc. First International Workshop onSediment Bypass Tunnels, VAW-Mitteilungen 232, ETH Zurich,Switzerland.[14] Felix, D., Albayrak, I., Boes, R.M., Abgottspon, A. (2017).Sediment transport through the power waterway and hydro-abrasive erosion on turbines. Proc. Hydro 2017 Conference,Seville, Spain: paper no. 27.07.[15] Felix, D. (2017). Experimental investigation on suspendedsediment, hydro-abrasive erosion and efficiency reductions ofcoated Pelton turbines, Doctoral Dissertation, VAW-Mitteilungen238 (R. Boes, ed.), ETH Zurich, Switzerland.https://doi.org/10.3929/ethz-b-000161430.[16] Boes, R.M. (Ed) (2016). Proc. International workshop ‘Dealingwith hydro-abrasive erosion at high-head hydropower plants’ -28th IAHR Symposium on Hydraulic Machinery and Systems,Grenoble, France, VAW-Mitteilungen 237, ETH Zurich,Switzerland. http://www.vaw.ethz.ch/das-institut/vaw-mitteilungen/2010-2019.html[17] IEC 62364 (2013). Hydraulic machines - Guide for dealing withhydro-abrasive erosion in Kaplan, Francis and Pelton turbines,Edition 1.0, International Electrotechnical Commission, Geneva,Switzerland.Dr. Ismail Albayrak is a researchscientist and lecturer at theLaboratory of Hydraulics,Hydrology and Glaciology (VAW)of ETH Zurich since 2011. He received his MSc. in hydraulicengineering from IstanbulTechnical University in 2003 and his PhD in the field ofenvironmental hydraulics at the Federal Institute ofTechnology in Lausanne (EPFL) in 2008. Dr. David Felix joined the VAW ofETH Zurich as a teaching assistantand scientific collaborator in2010. From 2012 to 2017 hefocused on the PhD-project onturbine erosion described in thepresent article. He continuesworking on suspended sediment and turbine erosion asa postdoctoral researcher. Dr. Lukas Schmocker joined thehydropower team of the SwissCompetence Centre of EnergyResearch – Supply of Electricity(SCCER-SoE) in 2014 with aresearch focus on hydropowerproduction and infrastructureadaption. In parallel, he is working as a project managerin flood management at the consulting company Basler& Hofmann.Dr. Robert M. Boes is Professorof hydraulic structures andDirector of the VAW at ETH Zurich.His research works focus onsustainable hydropower, reservoirsedimentation and floodpropagation, among others. He was formally the head of the Dam ConstructionGroup at TIWAG-Tiroler Wasserkraft AG, an Austrianutility. 

Research projects on reservoir sedimentation and sediment routing at vaw, ETH Zurich, Switzerland

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Research projects on reservoir sedimentation and sediment routing at vaw, ETH Zurich, Switzerland

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