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  • 1.
    Ahmad, Nawaz
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering. KTH Royal Institute of Technology.
    REACTIVE TRANSPORT MODELLING OF DISSOLVED CO2 IN POROUS MEDIA: Injection into and leakage from geological reservoirs2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The geological sequestration of carbon dioxide (CO2) is one of the options of controlling the greenhouse gas emissions. However, leakage of CO2 from the storage reservoir is a risk associated with geological sequestration. Over longer times, large-scale groundwater motion may cause leakage of dissolved CO2 (CO2aq).

    The objectives of this thesis are twofold. First, the modelling study analyzes the leakage of CO2aq along the conducting pathways. Second, a relatively safer mode of geological storage is investigated wherein CO2aq is injected in a carbonate reservoir. A reactive transport model is developed that accounts for the coupled hydrological transport and the geochemical reactions of CO2aq in the porous media. The study provides a quantitative assessment of the impact of advection, dispersion, diffusion, sorption, geochemical reactions, temperature, and heat transport on the fate of leaking CO2aq.

    The mass exchange between the conducting pathway and the rock matrix plays an important role in retention and reactions of leaking CO2aq. A significant retention of leaking CO2aq is caused by its mass stored in aqueous and adsorbed states and its consumption in reactions in the rock matrix along the leakage pathway. Advection causes a significant leakage of CO2aq directly from the reservoir through the matrix in comparison to the diffusion alone in the rock matrix and advection in a highly conducting, but thin fracture. Heat transport by leaking brine also plays an important role in geochemical interactions of leaking CO2aq

    Injection of CO2aq is simulated for a carbonate reservoir. Injected CO2-saturated brine being reactive causes fast dissolution of carbonate minerals in the reservoir and fast conversion of CO2aq through considered geochemical reactions. Various parameters like dispersion, sorption, temperature, and minerals reaction kinetics are found to play important role in the consumption of CO2aq in reactions.

  • 2.
    Ahmad, Nawaz
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering. Policy Wing, Ministry of Petroleum and Natural Resources, Government of Pakistan, Pakistan.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Bottacin-Busolin, Andrea
    Sanchez-Vila, Xavier
    Reactive transport modeling of leaking CO2-saturated brine along a fractured pathway2015In: International Journal of Greenhouse Gas Control, ISSN 1750-5836, E-ISSN 1878-0148, Vol. 42, p. 672-689Article in journal (Refereed)
    Abstract [en]

    One concern regarding the underground storage of carbon dioxide (CO2) is its potential leakage from reservoirs. Over short period of time, the leakage risk is related mainly to CO2 as a separate supercritical fluid phase. However, over longer periods upon complete dissolution of injected CO2 in the fluid, the leakage risk is associated with dissolved phase CO2. Over the geological time scales, large-scale groundwater motion may cause displacement of brine containing dissolved CO2 along the conducting pathways. In this paper, we present a comprehensive modeling framework that describes the reactive transport of CO2-saturated brine along a fracture in the clay caprock based on the future, hypothetical leakage of the dissolved phase CO2. This study shows that the transport of leaked dissolved CO2 is significantly retarded by a combination of various physical and geochemical processes, such as mass exchange between conducting fracture and the neighboring rock matrix through molecular diffusion, sorption and calcite dissolution in the rock matrix. Mass stored in aqueous and adsorbed states in the rock matrix caused retention of dissolved CO2 along the leakage pathway. Calcite dissolution reaction in the rock matrix resulted in consumption of leaking dissolved CO2 and reduced its mass along the leakage pathway. Consumption and retention of dissolved CO2 along the leakage pathway have important implications for analyzing the potential reduction of CO2 fluxes from storage reservoirs over large periods and long travel pathways.

  • 3.
    Ahmad, Nawaz
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering. KTH Royal Institute of Technology.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Jarsjö, Jerker
    Stockholm University, Sweden.
    Sanchez-Vila, Xavier
    Universitat Politècnica de Catalunya, UPC-BarcelonaTech, 08034 Barcelona, Spain.
    Bottacin-Busolin, Andrea
    Hellevang, Helge
    Non-isothermal reactive transport modelling of dissolved CO2 leaking through a fractured caprockManuscript (preprint) (Other academic)
    Abstract [en]

    Geological storage of CO2 is considered as one of the mitigation actions for climate change adverse effects. However, some fraction of CO2 dissolved in the brine following injection, may leak from the reservoir through permeable zones such as conducting fractures. In this study we perform the reactive transport modelling of single-phase brine saturated with dissolved CO2 (CO2aq) along a conducting fracture in a clay-rich caprock. This study investigates the role of temperature and various reaction systems on the fate of migrating CO2aq, its geochemical interactions with the carbonate minerals, its conversion in geochemical reactions and associated medium porosity and permeability evolutions along the transport pathway.About 0.64% of leaking CO2aq is found converted into other ions in its geochemical interactions with calcite (simplified geochemical system). Addition of mineral dolomite in the geochemical system (extended geochemical system) results in up to 11% higher mass conversion of CO2 in reactions as compared to the simplified geochemical system. Considering extended geochemical system and heat transport by moving brine resulted in about 27.34% higher mass conversion of CO2 in reactions as compared to the simplified geochemical system. A combination of extended geochemical system, heat transport and sorption resulted in about 82.59% higher mass conversion of CO2 compared to the simplified geochemical system. Leaking CO2aq travelled less than 250 m along the fractured pathway, for a velocity of nearly 19 m/year in the fracture, due to retardation caused by mass stored in aqueous and adsorbed states.

  • 4.
    Ahmad, Nawaz
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering. Ministry of Petroleum and Natural Resources, Pakistan.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Sanchez-Vila, X.
    Jarsjö, J.
    Bottacin-Busolin, A.
    Hellevang, H.
    Injection of CO2-saturated brine in geological reservoir: A way to enhanced storage safety2016In: International Journal of Greenhouse Gas Control, ISSN 1750-5836, E-ISSN 1878-0148, Vol. 54, p. 129-144Article in journal (Refereed)
    Abstract [en]

    Injection of free-phase supercritical CO2 into deep geological reservoirs is associated with risk of considerable return flows towards the land surface due to the buoyancy of CO2, which is lighter than the resident brine in the reservoir. Such upward movements can be avoided if CO2 is injected in the dissolved phase (CO2aq). In this work, injection of CO2-saturated brine in a subsurface carbonate reservoir was modelled. Physical and geochemical interactions of injected low-pH CO2-saturated brine with the carbonate minerals (calcite, dolomite and siderite) were investigated in the reactive transport modelling. CO2-saturated brine, being low in pH, showed high reactivity with the reservoir minerals, resulting in a significant mineral dissolution and CO2 conversion in reactions. Over the injection period of 10 yr, up to 16% of the injected CO2 was found consumed in geochemical reactions. Sorption included in the transport analysis resulted in additional quantities of CO2 mass stored. However, for the considered carbonate minerals, the consumption of injected CO2aq was found mainly in the form of ionic trapping.

  • 5.
    Ahmad, Nawaz
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering. KTH Royal Institute of Technology.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Sanchez-Vila, Xavier
    Bottacin-Busolin, Andrea
    The role of advection and dispersion in the rock matrix on the transport of leaking CO2-saturated brine along a fractured zone2016In: Advances in Water Resources, ISSN 0309-1708, E-ISSN 1872-9657, Vol. 98, p. 132-146Article in journal (Refereed)
    Abstract [en]

    CO2 that is injected into a geological storage reservoir can leak in dissolved form because of brine displacement from the reservoir, which is caused by large-scale groundwater motion. Simulations of the reactive transport of leaking CO2aq along a conducting fracture in a clay-rich caprock are conducted to analyze the effect of various physical and geochemical processes. Whilst several modeling transport studies along rock fractures have considered diffusion as the only transport process in the surrounding rock matrix (diffusive transport), this study analyzes the combined role of advection and dispersion in the rock matrix in addition to diffusion (advection-dominated transport) on the migration of CO2aq along a leakage pathway and its conversion in geochemical reactions. A sensitivity analysis is performed to quantify the effect of fluid velocity and dispersivity. Variations in the porosity and permeability of the medium are found in response to calcite dissolution and precipitation along the leakage pathway. We observe that advection and dispersion in the rock matrix play a significant role in the overall transport process. For the parameters that were used in this study, advection-dominated transport increased the leakage of CO2aq from the reservoir by nearly 305%, caused faster transport and increased the mass conversion of CO2aq in geochemical reactions along the transport pathway by approximately 12.20% compared to diffusive transport.

  • 6.
    Ahmad, Nawaz
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering. KTH Royal Institute of Technology.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Sanchez-Vila, Xavier
    Universitat Politècnica de Catalunya, UPC-BarcelonaTech, 08034 Barcelona, Spain.
    Bottacin-Busolin, Andrea
    The role of advection and dispersion in the rock matrix on the transport of leaking CO2-saturated brine along a fractured zoneManuscript (preprint) (Other academic)
    Abstract [en]

    CO2 that is injected into a storage reservoir can leak in dissolved form because of brine displacement from the reservoir, which is caused by large-scale groundwater motion. Simulations of the reactive transport of leaking CO2aq along a conducting fracture in a clay-rich caprock are conducted to analyze the effect of various physical and geochemical processes. Whilst several modelling transport studies along rock fractures have considered diffusion as the only transport process in the surrounding rock matrix (diffusive transport), this study analyzes the combined role of advection and dispersion in the rock matrix in addition to diffusion (advection-dominated transport) on the migration of CO2aq along a leakage pathway and its conversion in geochemical reactions. A sensitivity analysis is performed to quantify the effect of fluid velocity and dispersivity. Variations in the porosity and permeability of the medium are observed in response to calcite dissolution and precipitation along the leakage pathway. We observe that advection and dispersion in the rock matrix play a significant role in the overall transport process. For the parameters that were used in this study, advection-dominated transport increased the leakage of CO2aq from the reservoir by nearly 305%, caused faster transport and increased the mass conversion of CO2aq in geochemical reactions along the transport pathway by approximately 12.20% compared to diffusive transport. 

  • 7.
    Ahmad, Nawaz
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering. KTH Royal Institute of Technology.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Sanchez-Vila, Xavier
    Universitat Politècnica de Catalunya, UPC-BarcelonaTech, 08034 Barcelona, Spain.
    Jarsjö, Jerker
    Stockholm University, Sweden.
    Bottacin-Busolin, Andrea
    Hellevang, Helge
    Injection of CO2-saturated brine in geological reservoir: A way to enhanced storage safetyManuscript (preprint) (Other academic)
    Abstract [en]

    Injection of free phase supercritical CO2 into deep geological reservoirs is associated with risk of considerable return flows towards the land surface due to the buoyancy of CO2, which is lighter than the resident brine in the reservoir. Such upward movements can be avoided if CO2 is injected in the dissolved phase (CO2aq). In this work, injection of CO2-saturated brine in a subsurface carbonate reservoir is modelled. Physical and geochemical interactions of injected low-pH CO2-saturated brine with the carbonate minerals (calcite, dolomite and siderite) are investigated in the reactive transport modelling. CO2-saturated brine, being low in pH, shows high reactivity with the reservoir minerals, resulting in a significant mineral dissolution and CO2 conversion in reactions. Over the injection period of 10 years, up to 16% of the injected CO2 is found consumed in geochemical reactions. Sorption included in the transport analysis resulted in additional quantities of CO2 mass stored. However, for the considered carbonate minerals, the consumption of injected CO2aq is found mainly in the form of ionic trapping.

  • 8. Bandeira, Jefferson Vianna
    et al.
    Salim, Lecio Hannas
    Bomtempo, Virgilio Lopardi
    Moreira, Rubens Martins
    Brisset, Patrick
    Hughes, Catherine E.
    Pant, Harish Jagat
    Thereska, Jovan
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Nuclear Techniques for Monitoring Sediment Dynamics in the Coastal Zone2014In: ENGINEERING GEOLOGY FOR SOCIETY AND TERRITORY, VOL 4: MARINE AND COASTAL PROCESSES, CHAM: SPRINGER INT PUBLISHING AG , 2014, p. 151-155Conference paper (Refereed)
    Abstract [en]

    The knowledge of sediment transport in the coastal region is of vital importance to the management of this critical interface between land and sea, where most of the world population lives. For the assessment of sediment behaviour, hydraulic and sediment measurements, bathymetric survey, mathematical and physical models, are applied. Sediment tracers provide a unique capability for understanding sediment transport assisting in sediment management which cannot be obtained any other way, whether conventional monitoring or physical and numerical models because tracers integrate all the hydrodynamic actions in time and space. Computational fluid dynamics (CFD) is now an essential tool for the management of the natural systems and is increasingly used to study the fate and behaviour of particulates and contaminants. Tracer techniques are often employed to validate hydrodynamic models to enhance confidence in the predictive value of the models. In-situ detection afforded by the use of a radioactive tracer allows accurate quantitative determination of the rate of sediment transport, compared with other tracer methods. Also, it is cost effective and safe: its radiological impact to the environment is minimal. Several case studies, performed in different regions of the world, are presented.

  • 9. Boano, F.
    et al.
    Harvey, J. W.
    Marion, A.
    Packman, A. I.
    Revelli, R.
    Ridolfi, L.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Hyporheic flow and transport processes: Mechanisms, models, and biogeochemical implications2014In: Reviews of geophysics, ISSN 8755-1209, E-ISSN 1944-9208, Vol. 52, no 4, p. 603-679Article, review/survey (Refereed)
    Abstract [en]

    Fifty years of hyporheic zone research have shown the important role played by the hyporheic zone as an interface between groundwater and surface waters. However, it is only in the last two decades that what began as an empirical science has become a mechanistic science devoted to modeling studies of the complex fluid dynamical and biogeochemical mechanisms occurring in the hyporheic zone. These efforts have led to the picture of surface-subsurface water interactions as regulators of the form and function of fluvial ecosystems. Rather than being isolated systems, surface water bodies continuously interact with the subsurface. Exploration of hyporheic zone processes has led to a new appreciation of their wide reaching consequences for water quality and stream ecology. Modern research aims toward a unified approach, in which processes occurring in the hyporheic zone are key elements for the appreciation, management, and restoration of the whole river environment. In this unifying context, this review summarizes results from modeling studies and field observations about flow and transport processes in the hyporheic zone and describes the theories proposed in hydrology and fluid dynamics developed to quantitatively model and predict the hyporheic transport of water, heat, and dissolved and suspended compounds from sediment grain scale up to the watershed scale. The implications of these processes for stream biogeochemistry and ecology are also discussed.

  • 10.
    Bogdanski, Adam
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    SKRED I NIPOR OCH KONSEKVENSER FÖR VATTENKRAFTSANLÄGGNINGAR I ÅNGERMANÄLVEN.2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [sv]

    Detta examensarbete behandlar stabiliteten hos den typ av siltiga nipor som före-kommer längs med och i direkt anslutning Ångermanälven. Dessa sluttningar som i många fall antar karaktären av rasbranter har i många fall en alltför hög släntlutning för att kunna betraktas som stabila enligt traditionella beräkningsmetoder, men verkligheten visar att dessa beviserligen har den egenskapen att kunna stå kvar i mer extrema geometrier. Detta tillskrivs ofta egenskapen hos sand och framförallt silt att hysa negativa portryck samt cementeringseffekter till följd av mineralisering.

    Ägare av vattenkraftsanläggningar längs med Ångermanälven, till vilka e.on tillhör, har uttryckt en viss oro över vissa enstaka större skred som skulle kunna tänkas förekomma vid mer extrema tillfällen, där den stabiliserande förmågan blir reducerad och risken för att dessa generera flodvågor av det större slaget, ökar. Detta kopplat till andra omständigheter vid dessa tidpunkter som höga vattenflöden och minskad av-bördningskapacitet i själva dammen, gör att det finns ett intresse i branschen att kart-lägga stabiliteten hos slänter i anslutning till vattendrag, inte minst då skred generar drivgods, vilket kan leda till igensatta utskov.

    Studien har behandlat Ångermanälven från kraftverket i Sollefteå C upp till Nämforsens kraftverk i Näsåker och har ur stabilitetssynpunkt fokuserat på två slänter, en i Remsele och den andra i Mo-Norrtannflo, där det för den förstnämnda fanns en del material tillgängligt från tidigare undersökningar, medan det för den andra krävdes undersökningar i fält för att fastställa dess egenskaper.

    Av de analyser som gjorts framgår att de studerade objekt och området närmast om-kring dem verkar vara stabila mot de djupare skred som befarades. Däremot tycks ytli-gare skred och erosion utgöra ett större problem, och bör analyseras och karteras mer för området som helhet för att fastställa den egentliga förkomsten av dessa, i synnerhet då just ytligare skred som berör större ytor kan bidra med stora mängder drivgods.

  • 11.
    Bohlin, Caroline
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    CFD-BERÄKNING AV INSTRÖMNING TILL ETT VATTENKRAFTVERK: –EN FALLSTUDIE AV FINNFORS KRAFTVERK2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [sv]

    I Sveriges kalla klimat innebär isrelaterade problem årliga produktionsförluster för vattenkraftföretagen. Kravisbildning på intagsgrinden till ett vattenkraftverk betyder att den grindarea genom vilken vatten kan strömma in reduceras och inströmningsförlusterna ökar. De förebyggande åtgärderna handlar ofta om att sänka vattnets ythastighet tillräckligt mycket för att ett stabilt istäcke ska kunna utbredas. Istäcket isolerar vattnet från fortsatt nedkylning så att temperaturen i vattnet inte understiger 0 °C och kravisproduktionen i vattnet upphör.

    I detta examensarbete tillämpas CFD-beräkningar för att åskådliggöra hastighetsfördelningen i magasinet vid Finnfors kraftverk med dess nuvarande batymetri och med modifierade batymetrier motsvarande potentiella åtgärder för att sänka vattnets hastighet. Anläggningsägaren Skellefteå Kraft hade identifierat två problem som ansågs kunna bidra till turbulens och höga inströmningshastigheter och utöver dessa kunde simuleringar med magasinets nuvarande batymetri identifiera i vilka områden åtgärder borde genomföras. Av de fem utvärderade åtgärdsalternativen ledde inget till att hastigheterna helt understeg de kritiska gränserna för då ett istäcke kan lägga sig vid en vattenföring på 225 m 3/s, däremot reducerades storleken på områdena med höga hastigheter. Valideringen ökade resultatens tillförlitlighet och denna studie visar därmed hur CFD-beräkningar kan tillämpas för att utvärdera vilken effekt en bottenmodifiering skulle få för strömningen i en älvfåra. Detta kan utgöra användbart underlag i arbetet med att förbättra produktionskapaciteten i befintliga vattenkraftverk.

  • 12. Borghei, Seyed Mahmood
    et al.
    Nekooie, Mohammad Ali
    Sadeghian, Hadi
    Ghazizadeh, Mohammad Reza Jalili
    Parvaneh, Ali
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Javaheri, Amir
    Kabiri-Samani, Abdorreza
    Discussion: Triangular labyrinth side weirs with one and two cycles2016In: Proceedings of the Institution of Civil Engineers: Water Management, ISSN 1741-7589, E-ISSN 1751-7729, Vol. 169, no 3, p. 111-114Article in journal (Other academic)
  • 13.
    Bramsäter, Jenny
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Closure of Lilla Bredsjön Tailings Dam: an Evaluation of the Long-Term Dam Safety Measures2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The mining industry contributes to enormous amounts of waste all over the world, which places high demands on tailings dams. In Sweden, there are strict regulations regarding the management and treatment of tailings dams, but some dams that were built before these regulations existed still pose a threat to the environment. Lilla Bredsjön in Dalarna, Sweden, is an example of an old tailings dam that has not been treated properly. Boliden, which is the owner of the dam, and the county board of Dalarna are currently in meetings regarding the responsibilities of old polluted sites in Garpenberg, where Lilla Bredsjön is included. This study aims to investigate possible remediation measures of the dams at Lilla Bredsjön in order to achieve long- term stability upon closure of the facility.

    Lilla Bredsjön is 350 000 m2 large and contains three impoundments; dam 1 to the east, dam 2 to the south and dam 3 to the north. Dam 1 is seven meters at its highest point whereas dam 2 and 3 both are three meters high. All of the dams are classified to a consequence level of 3, meaning that the consequences in case of a failure would be negligible. They are built using the centerline method with impermeable cores of moraine. The tailings are partly covered with sludge mixed with biomass ash, but no proper closure method have been implemented.

    A geotechnical investigation was conducted to obtain more information about the geometry, construction and foundation of each dam. It could be observed that dam 1 consisted of a moraine core and support fill, both constructed using the Christmas tree principle. Dam 2 consisted of a coarse and fine filter in the upstream part of the dam, whereas the rest of the dam consisted of a moraine core. Dam 3 consisted of tailings and a moraine core, and was like dam 1 also constructed using the Christmas tree principle. The downstream slopes of all dams are moreover very steep with slope angles of approximately 34o. Seepage and stability calculations were therefore performed in the software GeoStudio.

    In GeoStudio, two different analysis tools were used; SEEP/W to calculate seepage and SLOPE/W to calculate slope stability. Four hydraulic load cases were analyzed in the calculations: present conditions, flooded conditions, potential maximum seepage and present conditions with lower permeability of the tailings. The result shows that all of the dams are unstable in their present con- ditions, both with original and lower permeability of the tailings, as well as at flooded conditions. The required safety factor is however fulfilled at potential maximum seepage.

    The stability highly depends on the pore pressure inside the dams, which in turn depends on the choice of closure method. Based on the result from the stability calculations it can be concluded that if a dry cover is chosen as the closure method, it will probably be enough to reinforce the existing dams to achieve long-term stability. If, on the other hand, a raised groundwater level is chosen, more extensive solutions in terms of for example completely new impoundments directly downstream of the existing ones are most likely needed. Before a decision regarding the closure method is taken, it is hence very difficult to come to a conclusion regarding suitable remediation measures of the dams.

  • 14.
    Brandner, Hanna
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Idenitfying the Influential Factors of the Temporal Variation of Water Consumption: A Case Study using Multiple Linear Regression Analysis2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis is a part of the water development project conducted by Svenskt Vatten, which is the Swedish Water and Wastewater Association (SWWA) as well as Tyréns, a consultancy company with offices based in Stockholm, Sweden. Prior to this thesis work, a quality assessment was conducted for some of the locations provided by municipalities in Sweden. This thesis builds upon the revised water consumption data, and also continues to work with validating and modifying the water measurement data in order to proceed with the next step of the water development project, which is to identify any trends in the temporal variation of water consumption. The main objective of this thesis work is to investigate the influence of climatic, time-related and categorical factors on water consumption data collected for different regions in Sweden, and includes a number of different sectors such as residential, industrial and agricultural water user sectors. For the analysis of data, spectral analysis and sinusoidal modelling will be applied in order to find the periodicity of the data, and then simulate the fitted sinusoidal equation to the observed water consumption data for the hourly interval period. Multiple linear regression analysis is then used to assess what independent variables such as climate, time-related and categorical variables can explain the variation in water consumption over hourly and daily periods of time. 

    Spectral analysis identifies high peaks in the spectral density of the data at 12 and 24 hour cycles, for the hourly water consumption data. For the total daily consumption of water, there is a peak at 7 days, which clarifies that there is a weekly pattern occurring throughout the year. The results from the simple linear regression analysis, where the linear relationship between temperature and water consumption was determined, reveals that the water consumption tends to increase within an increasing temperature, where in Lönashult, Alvesta municipality the water demand increased by 5.5% with every 2 ºC rise in temperature, at a threshold of 12 ºC. For Kalix municipality the three areas selected have around 1-2 % increase in water demand with every 2 ºC rise in temperature for the period of May to December. In Gothenburg, areas that were mixed villa areas or areas with summer homes there was a rise of around 2-12 % in water demand, however areas that are situated in the inner city Gothenburg, or that have majority student housing, the water consumption tends to decrease by 2-7% in water demand with every 2 ºC rise in temperature, with a threshold of 12 ºC.

    In multiple regression analysis, the hourly water consumption results in adjusted R2 values were in the range from 0.58 to 0.87 (58-87%) for the best model approach and therefore has a significant relationship between water consumption and the explanatory variables chosen for this study. For the daily water consumption, the adjusted R2 values were in the range of 0.22-0.83 (22-83%).  The adjusted R2 values are lower for certain areas and can be explained by a number of factors, such as the different variables used for the daily water consumption analysis, as variables that explain more the periodicity of the data such as the sinusoidal fitted variable and hourly or night/day changes in consumption are not included. As well as this, not all independent variables such as the climate variables were available or complete for particular time periods, and also errors in the data can lead to a significantly lower R2 value. 

  • 15. Bresciani, E.
    et al.
    Gleeson, T.
    Goderniaux, P.
    de Dreuzy, J. R.
    Werner, A. D.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Zijl, W.
    Batelaan, O.
    Groundwater flow systems theory: research challenges beyond the specified-head top boundary condition2016In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 24, no 5, p. 1087-1090Article in journal (Refereed)
  • 16.
    Chatzakis, Alexandros
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Calibration of a 2D hydrodynamic model for flood inundation extent using aerial photographs: A case study of the Hallsberg flood event in 5-9 September 20152017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Alteration of rainfall patterns is one major impact of climate change. Rainfall events with big precipitation volumes under short periods of time are predicted to become even more frequent in higher latitude regions, including Sweden. One characteristic example of such an intense rainfall occurred between the 5th and 6th of September 2015 in Hallsberg, a city in central Sweden, where approximately 105 mm of rain fell under 24 hours, causing severe flooding in the city. In order to be able to predict flood cases like the aforementioned one, hydrodynamic models are employed to simulate floods and investigate rainfall scenarios so that the competent authorities can take precaution measures. However, due to lack of calibration data most of flood models are not validated and are comprised of substantial uncertainty.

    This report aims to study the Hallsberg flood event in September 2015 by calibrating a hydrodynamic model using aerial photographs for the flood inundation extent. The utilized model is MIKE 21, which is a 2D overland flow model developed by DHI. Contrary to the common practice in flood studies where inclusion of the infiltration capacity is implemented with an arbitrary reduction of the rain volume, the infiltration module of MIKE 21, which is a new development in the model, was utilized. Apart from the inundation extent, the outputs were also evaluated for the water depth in two points based on a photograph captured from the streets of the affected area, the description of the course of events for the timing of flood’s culmination and the water volume on the pixels that were erroneously simulated as flooded.

    The results presented a high degree of agreement with the observations. The parameter of surface resistance, expressed as Manning’s “M”, was found to be of paramount importance with the suitable values for undeveloped areas being below 5. In addition, the culverts’ limited capacity played an important role in the flooding of the city and hence including them in the simulations is crucial. Finally, utilization of the infiltration module resulted in a higher accuracy of 8.3% although it can be considered more of an arbitrary deduction of water as some of the parameters used in it are not physically well justified. 

  • 17.
    Dargahi, Bijan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Kolluru, V.
    Cvetkovic, Vladimir
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Multi-layered stratification in the Baltic Sea: Insight from a modeling study with reference to environmental conditions2017In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 5, no 1, article id 2Article in journal (Refereed)
    Abstract [en]

    The hydrodynamic and transport characteristics of the Baltic Sea in the period 2000-2009 were studied using a fully calibrated and validated 3D hydrodynamic model with a horizontal resolution of 4.8 km. This study provided new insight into the type and dynamics of vertical structure in the Baltic Sea, not considered in previous studies. Thermal and salinity stratification are both addressed, with a focus on the structural properties of the layers. The detection of cooler regions (dicothermal) within the layer structure is an important finding. The detailed investigation of thermal stratification for a 10-year period (i.e., 2000-2009) revealed some new features. A multilayered structure that contains several thermocline and dicothermal layers was identified from this study. Statistical analysis of the simulation results made it possible to derive the mean thermal stratification properties, expressed as mean temperatures and the normalized layer thicknesses. The three-layered model proposed by previous investigators appears to be valid only during the winter periods; for other periods, a multi-layered structure with more than five layers has been identified during this investigation. This study provides detailed insight into thermal and salinity stratification in the Baltic Sea during a recent decade that can be used as a basis for diverse environmental assessments. It extends previous studies on stratification in the Baltic Sea regarding both the extent and the nature of stratification.

  • 18.
    Ekström, Ingvar
    et al.
    Sweco.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Berg, Mikael
    Improving spillway discharge safety at Bergeforsen2011Conference paper (Refereed)
    Abstract [en]

    Bergeforsen is a 35 m high embankment dam. The technical discharge capacity of the existing spillway is 2300 m3/s at full reservoir retention level (FRRL). To meet new design flood criteria a first major rehabilitation was carried out 2003, which allowed discharge of an extreme flood at a water level higher than the FRRL. Recent underwater inspections of the spillway and energy converter have however revealed a need for rehabilitation and adaptation of the concrete structures to the design flood flow conditions. To make it possible to take the spillway out of operation for the time period required for adequate repairs it has been decided to rebuild the dam, adding an alternative spillway structure that will serve as discharge facility during the upgrade of the existing spillway. For this reason, a new 25-m gated spillway, with a stilling basin followed by a curved tunnel section, will be constructed in the left river bank. Once the existing spillway is rehabilitated the combined discharge capacity will make it possible to safely pass the revised design flood at a reservoir level not exceeding the FRRL. A physical model was built to asssit in the design decision, the purpose of which is to verify and optimize engineering solutions for increased discharge capacity, so that the design flood is released without jeopardizing the stuctural integrity of the dam.

  • 19.
    Ekström, Ingvar
    et al.
    Sweco.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Mören, Lena
    Cederström, Malte
    Vattenfall AB.
    Adapting Ligga to higher design flood, spillway channel modification through physical & numerical modeling2007Conference paper (Refereed)
    Abstract [en]

    As part of Vattenfall’s dam-safety program, Ligga dam is to be rebuilt for higher safety level. Besides diverse measures, the spillway channel will be modified. The channel is bounded by natural bedrock. Spillway operations during the past years have evidenced severe erosion and damages in the fractured rock. Rock instability becomes visible even at moderate spillway discharges 800 – 900 m3/s. The updated design-flood of the dam is in the order of the magnitude of 2000 m3/s. To adapt the dam to the higher flood, the spillway channel has to be re-shaped, so that the flood is safety released and the structural integrity of the embankment dam is maintained. As a cost-effective alternative, excavation is recommended, as a large volume of rock material is required for stabilizing the dam and for replacing the slope protection upstream. To achieve satisfactory flow behaviors, hydraulic model tests are made to examine and optimize excavation possibilities. The re-shaping of the waterway is complicated by the fact that the existing channel bends in plan and the excavation must follow roughly the same curvature. Considerations are also given to exemption of the dam toe from erosion and the forest on the left riverside from being flooded. Computer simulations of water-rock interaction are made with the commercial code UDEC. Against previous flood release records, the numerical model of rock erosion is calibrated and uses measured water level, flow velocity and dynamic water pressure in the model as input data. Results show that the new waterway configuration provides proper flow patterns and the rock foundation after reinforcement is not subjected to unacceptable damage at spillway discharges up to the design flood.

  • 20.
    Ekwall, Jakob
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering. KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Water Resources Engineering.
    Kvalitetskontroll av Vattenförbrukningsdata: Ursprung till Fel och Osäkerheter i mätdata från Göteborgs kommun2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 21.
    Ferdos, Farzad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    A study of turbulent flow in large-scale porous media at high Reynolds numbers. Part I: numerical validation2016In: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 54, no 6, p. 663-677Article in journal (Refereed)
    Abstract [en]

    Analyses of turbulent flows through the downstream slopes of embankment dams are important for dam safety assessments, especially considering high-risk scenarios such as a sudden release of water due to internal erosion. Flow prediction is difficult in such situations due to coarseness of construction materials and high Reynolds numbers. The present study addresses this issue through comprehensive numerical modelling. The novelty of the proposed approach lies in a combination of large-scale experiments and three-dimensional numerical simulations, leading to a fully calibrated and validated model that is applicable to flows through cobble-sized materials (100–160 mm in diameter) at high Reynolds numbers (>104). Comparing the results of the standard turbulence models to data from the large-sale experiments, the renormalization group theory-based model yielded the smallest relative errors based on the hydraulic gradients. Considering the flow field, the turbulent shear stress increased by a factor of 17, and the time-averaged vorticities intensified by factors of 2, 6 and 10 for vorticities in the x-, y- and z-directions, respectively, due to the presence of cobbles.

  • 22.
    Ferdos, Farzad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    A study of turbulent flow in large-scale porous media at high Reynolds numbers. Part II: flow physics2016In: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 54, no 6, p. 678-691Article in journal (Refereed)
    Abstract [en]

    The evaluation of hydraulic performance of coarse porous media at high Reynolds numbers is of significant importance for dam safety assessment. To address this task, the present study uses a numerical approach based on a rigorous theoretical framework. The novelty of the study lies in the application of a fully calibrated and validated numerical three-dimensional model and a set of modified equations for momentum transfer and the associated coefficients for flow in porous media. A Lagrangian particle tracking model was used to estimate the lengths of the flow channels that developed in the porous media. Gamma distributions were fitted to the normalized channel lengths, and the scale and shape parameters of the gamma distribution were found to be Reynolds number dependent. These shape parameters can be estimated from the suggested polynomial equations. The proposed normalized length parameter can be used to evaluate permeability, energy dissipation, induced forces, and diffusion. It was found that shear forces exerted on the coarse particles depend on the inertial forces of the flow and can be estimated using the proposed equation for the developed turbulent flows in porous media.

  • 23.
    Ferdos, Farzad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Solari, Luca
    Mechanism of concentrated leak erosion phenomenon in embankment dams2016Manuscript (preprint) (Other academic)
  • 24.
    Ferdos, Farzad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Solari, Luca
    Mechanism of suffusion erosion phenomenon in embankment dams2016Manuscript (preprint) (Other academic)
  • 25.
    Ferdos, Farzad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Rosén, Lars
    Quantitative environmental footprints and sustainability evaluation of contaminated land remediation alternatives for two case studies2013In: Remediation Journal, ISSN 1051-5658, E-ISSN 1520-6831, Vol. 24, no 1, p. 77-98Article in journal (Refereed)
    Abstract [en]

    Since the US Environmental Protection Agency (US EPA) launched its "green remediation" program and EU member states began to reassess their national regulations for environmental remediation in order to reach a Europe-wide consensus on policy and standards, the need and interest for sustainable remediation of contaminants from brownfields has grown considerably. Concomitantly, the ability to calculate and assess the suitability as well as the environmental footprints and associated risks of a growing number of remediation techniques has become a priority. The authors quantitatively evaluate the differences between various remediation techniques, and for this purpose, a number of ex situ and in situ remediation techniques are adapted to model 21 remediation scenarios for two contaminated sites in the Gothenburg region of Sweden: the Bohus Varv site on the Göta älv river bank and the Hexion site in Mölndal. A wide range of quantitative results for these models are presented, compared, and analyzed. Based on the results from both projects, it is concluded that: (1) remediation techniques requiring long distance residual transportation have significant footprints, except the transportation of contaminated residuals by train due to Swedish energy production conditions; (2) residual transportation by ship results in much higher SOx, NOx, and particle releases compared to the other alternatives; and (3) residual transporation by truck results in high accident risks. Finally, activities powered by electricity result in a reduced footprint compared to activities powered by fossil fuels, considering Swedish energy production conditions. The authors conducted a cross-benefit analysis of SiteWiseTM applications which recognizes its potential as a tool for presenting life cycle assessment analyses with appropriate system boundary definitions and an easy inventory analysis process. Results from this tool provide valuable support to decision makers aiming at more sustainable remediation.

  • 26.
    Ferdos, Farzad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Ekström, Ingvar
    Hydraulic Conductivity of Coarse Rockfill used in Hydraulic Structures2015In: Transport in Porous Media, ISSN 0169-3913, E-ISSN 1573-1634, Vol. 108, no 2, p. 367-391Article in journal (Refereed)
    Abstract [en]

    Internal erosion is a major cause of embankment dam failure. Unravelling and instability of the downstream slope, initiated by internal erosion and leakage through the dam core, is one of the most likely breach mechanisms for large, zoned embankment dams. To be able to model this mechanism, the relationship between the hydraulic gradient and the flow velocity for the coarse rockfill material must be understood. Because most studies of this topic have focused on the flow parameters in gravel-size materials with Reynolds (Re) numbers lower than 25,000, permeability measurements are needed coarser rockfill material under heavily turbulent flow regimes prevailing in rockfill material under certain design flow scenarios. This paper presents the set-up and results of a series of field and laboratory experimental studies and the subsequent data interpretation, from which relevant hydraulic conductivity parameters, defined in applicable flow laws, were extracted. This study demonstrates that the exponent of a power flow law relating the hydraulic gradient and the flow velocity is Re number dependent for pore Re numbers 60,000. The power remains constant (Re number independent) above this Re number threshold for the fully developed turbulent regime. This validity threshold as well as the constant behaviour also applies if the flow law is written in a quadratic form. The aforementioned threshold lies beyond the ranges investigated experimentally by previous researchers. The experiments in this study examined Re numbers as large as 220,000 for grain-diameter distributions in the range 100-160 mm and as large as 320,000 in the range 160-240 mm.

  • 27.
    Ferdos, Farzad
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Characterization of hydraulic behaviours of coarse rock materials in a large permeameter2013In: Journal of Geoscience and Environment Protection, ISSN 2327-4336, Vol. 1, no 3, p. 1-6Article in journal (Refereed)
    Abstract [en]

    The hydraulic behavior of a rock material structure is a major feature for its design and safety assessment. Similar to all other physical prob-lems, in order to enclose the governing equations systems and achieve a solution, the hydraulic characteristics of these materials need to be determined experimentally and implemented then into adopted thermo-dynamical models. This paper covers the process of the design, con-struction and operation of an experimental rig built for this specific purpose. Using the constructed large-scale permeameter, tests have been conducted. The non-linear hydraulic behavior of various materials under extreme turbulent conditions, where Reynolds number reaches un-precedented values, has not been studied before. Preliminary results are presented and discussed.

  • 28.
    Genty, Stanislas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Numerical hydraulic modeling of urban waste water collecting systems: Working Project at Chazelles-sur-Lyon, France2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Urban waste water collecting systems are designed to convey domestic, industrial and storm water. When sizing sewer network, heavy rainfall must be considered to provide the needed hydraulic capacity for collection.

    Maintenance is also required in order to avoid anomalies such as inflow, infiltration and unusual polluted discharges from Combined Sewer Overflows (CSOs). Inflow and infiltration decrease the treatment yield at the Waste water Treatment Plant

    (WWTP) and participate in hydraulic overloads and overflows. CSOs have a direct impact on the pollution of water bodies and must be strictly sized and monitored. Detecting sizing and maintenance anomalies is crucial to ensure public health and a good status of our natural environment. Today, numerical hydraulic models support consulting engineers in assessing overflows then in choosing the best technical and cost-effective scenario.

    The objectives of this paper are to review the dysfunctions of collecting system and to understand how a numerical hydraulic model is constructed, calibrated and then used to establish a Corrective Action Plan (CAP).

    My master thesis is based on a working project achieved at SAFEGE (Group SUEZ Environnement) in the Urban Hydraulics Department in Lyon (Rhône-Alpes, France) between September 2013 and February 2014. The paper will present some outcomes obtained from an Urban Hydraulic Project at Chazelles-sur-Lyon (Rhône-Alpes, France) in the South West of Lyon. Mike Urban is the software - developed by the company DHI Water- used for the numerical hydraulic modeling.

  • 29. Klos, R. A.
    et al.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Uncertainties in doses from agricultural ecosystems following conversion from wetlands2013In: 14th International High-Level Radioactive Waste Management Conference, IHLRWMC 2013: Integrating Storage, Transportation, and Disposal, 2013, p. 1024-1031Conference paper (Refereed)
    Abstract [en]

    Agricultural ecosystems dominate human exposure to environmental concentrations of radionuclides following release from geologic disposal facilities. Although natural ecosystems have received considerable attention in the past decade their low productivity requires large areas of land to meet dietary requirements leading to a high a high spatial dilution when uncontaminated food sources are included. Additionally, long accumulation times may be anticipated. Accumulation in natural ecosystems followed by exposure in agricultural ecosystems is of interest. The transition period can be short, with residual activity inventories remaining unchanged. Doses in the agricultural system therefore begin with relatively high initial radionuclide concentrations in the soil column. Timescales for subsequent leaching are determined by the retention characteristics of the soils and ecosystem. There is a question of reliability of the models used in this context because of the rapid transition. This paper describes a sensitivity analysis carried out using an advanced 10-layer soil model of the upper one metre of an agricultural soil underlain by a simple geosphere-biosphere interface. As well as soil chemistry and hydrology, results here emphasise the importance of the representation of the soil-plant interaction. The mechanics of the transition between natural and managed ecosystems are also shown to be important.

  • 30. Kung, C. S.
    et al.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Energy interpretation of hydraulic transients in pipelines1993In: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 31, no 6Article in journal (Refereed)
    Abstract [en]

    The energy concept sheds light upon the hydraulic system that comprises the throttled surge tank, the tunnel and the penstock. The mathematical manipulation of the governing differential equations of water hammer yields an energy (power) equation in point form. By integration with respect to pipe distance, this relation is extended first to an individual pipe, then to the surge-tank system with branching connection. The system energy (power) equation states the relationship between the total (internal plus kinetic) energy, the convective energy, the work done on the system and the energy dissipation. A case study identifies the conversion between the internal and kinetic energy, and quantifies the behaviour and magnitudes of related energy components of the system.

  • 31. Kłos, R. A.
    et al.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Site specificity in advanced dose assessment modeling2015In: 15th International High-Level Radioactive Waste Management Conference 2015, IHLRWM 2015, American Nuclear Society, 2015, p. 447-454Conference paper (Refereed)
    Abstract [en]

    Final disposal of high-level radioactive waste is not straightforward. The aim is to isolate the waste from the biosphere over timescales that are long compared to recorded human history. Aside from the complex engineering requirement there is a highly sensitive legal requirement, embodied in the national regulatory framework relevant to the disposing organization, to provide a proportionately detailed assessment of the potential radiological impact of the disposal system on the health of future generations. Siting, construction and disposal is an iterative process. It starts with site selection, at early stages generic interpretations are appropriate. At later stages-e.g., construction licensing-the proponent must show a detailed understanding of the repository design, construction and potential radiological impact of any release to the human environment in the biosphere. Taking the example of the Swedish Nuclear Waste Management Company's 2011 license application for the construction of a spent fuel repository on the Baltic Coast of east-central Sweden, this paper looks at the role played by the incorporation of site-specific details in the dose assessment modeling that support the review of the license application. Implications of lessons learned in the Swedish context are extended to the international waste disposal community.

  • 32. Liang, S. D.
    et al.
    Zhang, Y. L.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    An experimental study on pile scour mitigating measures under waves and currents2015In: Science China Technological Sciences, ISSN 1674-7321, Vol. 58, no 6, p. 1031-1045Article in journal (Refereed)
    Abstract [en]

    An experimental study has been carried out to investigate effects of four flow-altering scour countermeasures placed around a foundation pile under currents only as well as under coexisting waves and currents. The countermeasures are sacrificial piles, downstream bed sill, sleeve and slot in the pile. Their arrangements follow the suggested optimal configurations, with some of them slightly modified. In terms of the evolution of scour depth and bed topography around the pile, the scour countermeasures are evaluated, subjected to steady currents with or without irregular waves. A comparison between maximum scour depth with the countermeasures and one without the countermeasures demonstrates the efficiency of countermeasures. All the tested scour measures reduce the scour depth by 17.6%–42.6% under the action of currents only and 5.8%–24.0% under the combined action of both currents and waves. The results also show that it takes a shorter time for the scour depth to reach its equilibrium with the measures under either coexisting currents and waves or currents only than ones without the measures.

  • 33.
    Liang, SD
    et al.
    Tsinghua University.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    An experimental study of scour countermeasures for offshore piles in marine environment2013Conference paper (Refereed)
    Abstract [en]

    Four commonly used scour countermeasures, i.e. riprap, horizontal collar, tetrahedral frame and the combination of riprap and tetrahedral frames around a cylindrical pile are tested in a current-wave flume to examine their effects on scouring. The evolution of scour depth around the pile in regard of the scour countermeasures, subjected to the action of steady currents with or without irregular waves, and the bed topography change around the pile are evaluated. The range of scour and its erosion volume are estimated. A comparison between scour parameters with and without the countermeasures demonstrates the efficacy of the countermeasure in terms of the maximum scour depth. All of the tested countermeasures reduce the scour depth significantly. However, depending on the type of scour countermeasure adopted, the scour depth reduction efficacy varies considerably. The tests also show that it takes a longer time to reach the maximum scour depth in the current-wave conditions than only in the current conditions. For the majority of the cases, the scour range and volume subjected to the combined current-wave action is larger than only to the current action.

  • 34. Lin, C.
    et al.
    Kao, M. -J
    Wong, W. -Y
    Tsai, C. -P
    Chang, K. -T
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Characteristics of flow separation and hydraulic jump during run-down motion of shoaling solitary wave traveling over steep sloping bottom2016In: Proceedings of the International Offshore and Polar Engineering Conference, International Society of Offshore and Polar Engineers , 2016, p. 724-731Conference paper (Refereed)
    Abstract [en]

    The features of velocity fields for the evolution of shoaling solitary wave, having a wave-height to water-depth ratio of 0.363 and propagating over a 1:3 sloping bottom, are investigated experimentally. A flow visualization technique using particle trajectory method and a high-speed particle image velocimetry (HSPIV) system employing a high-speed digital camera were used. This study mainly focuses on the occurrence of separated shear layer from the sloping bottom, evolved vortex structure, subsequent hydraulic jump, and curling jet of the backward breaking wave impinging upon the free surface of retreated flow during the run-down motion of the shoaling solitary wave.

  • 35. Lin, C
    et al.
    Kao, MJ
    Lo, LF
    Yeh, PH
    Raikar, RV
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Huang, H
    Similarity velocity profile of vortex flow in the cavities between girders under a partially inundated bridge deck2014Conference paper (Refereed)
    Abstract [en]

    This paper presents the experimental results on similarity velocity profile of vortices inside the cavities, formed between two neighboring girders, under a partially inundated bridge deck. Particle image velocimetry (PIV) and flow visualization technique are both employed to explore the flow field. The approaching flow is subcritical with Froude number varying in the range 0.137–0.381. The velocity characteristics of vortex structure inside the cavities under a partially inundated bridge deck, where water is fully occupied without air-pocket, are mainly investigated. The similarity profile of the azimuthal velocity along an arbitrary line, passing through the vortex core, is uniquely obtained using the measured azimuthal velocities for two different flow types. The selection of the characteristic length and velocity scales used for obtaining the similarity profile is discussed in this study.

  • 36. Lin, C.
    et al.
    Lu, C. H.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Liu, Ting
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Study on water flow field around a stationary air bubble attached at the top wall of a Circular Pipe2013In: Computational methods in multiphase flow VII, WIT Press, 2013, p. 323-338Conference paper (Refereed)
    Abstract [en]

    The presence of bubbles in a pipeline is thought to be one of the reasons to cause the hydraulic-electrical and hydraulic-mechanical facility systems to lose their efficiency. From previous research, the bubble also reduces the effective pipe cross section, which results in a reduction in pipe capacity. The efficiency and service life of pumps and turbines are reduced and shortened consequently. It may even create the interruption of the flow field within blowout phenomenon. As a result, the presence of a bubble in the pipeline is anticipated to create potential hazards. Therefore, it is very interesting to make clear the corresponding variation of a water flow field around a stationary air bubble attached at the top inner-wall of pipe due to the surface problems in contact mechanism of these three phases among the solid wall of pipe, stationary air bubble, and ambient water flow. This study applied flow visualization techniques and high time-resolved PIV to investigate the characteristics of a flow field around a stationary bubble in a fully-developed horizontal pipe flow. Experiments were carried out in a pipe having a constant inner diameter of 9.60 cm and a length of 260.0 cm, yet varied with different bubble volumes (or lengths). Two settling water chambers with different still water levels were connected to both ends of the circular pipe. Titanium dioxide powder being uniformly dispersed in the pipe flow was used as a tracer both for flow visualization tests and for PIV measurements. The results show that a horseshoe vortex and reverse flow at the upstream and downstream of the bubble respectively are commonly seen in all test cases. The experimental results also show that the shape and volume of a bubble highly affect the flow field in the surroundings of the stationary air bubble. Since the bubble surface is slippery, flow velocity exists on the surface of a bubble. As a result, the reverse flow at the end of a long-flat bubble would not affect the velocity on the bubble surface.

  • 37. Lin, C.
    et al.
    Yu, S. -M
    Wong, W. -Y
    Tzeng, G. -W
    Kao, M. -J
    Yeh, P. -H
    Raikar, R. V.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Tsai, C. -P
    Velocity characteristics in boundary layer flow caused by solitary wave traveling over horizontal bottom2016In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 76, p. 238-252Article in journal (Refereed)
    Abstract [en]

    The characteristics of horizontal velocity in the bottom boundary-layer flow induced by a solitary wave propagating over a horizontal bottom are presented experimentally, using high-speed particle image velocimetry (HSPIV). The ratio of wave height to water depth varies from 0.096 to 0.386 and the flow inside the boundary layer is laminar. The results show that the horizontal velocity profiles can be mainly classified into two categories with respect to the passing of the solitary wave-crest at the measuring section: the pre-passing (or acceleration) phases under favorable pressure gradient and post-passing (or deceleration) phases under adverse pressure gradient. For the velocity distributions obtained during the pre-passing phases, a nonlinear regression analysis was used to precisely determine the time-dependent characteristic length and velocity scales underlying these profiles. A similarity profile of the horizontal velocity is established first using the time-dependent free-stream velocity and boundary layer thickness as the characteristic velocity and length scales, respectively. In addition, the displacement thickness, the momentum thickness, and the energy thickness are also considered as alternative length scales. All these four representative thicknesses are closely related to each other, demonstrating that any one amongst them can be regarded as the characteristic length scale. The forms of similarity profiles for the non-dimensional velocity distributions are somewhat analogous to the results of steady boundary layer flow over a thin plate under with pressure gradient, but with different coefficients or powers. While during the post-passing phases, flow reversal which acts like an unsteady wall jet and moves in the opposite direction against the wave propagation occurs after the passage of solitary wave-crest. The thickness of flow reversal layer increases with time. A similarity profile is proposed for the velocity distributions corresponding to occurrence of the extreme value in the maximum negative velocity of flow reversal. Variations of the maximum negative velocity and the thickness of flow reversal with the time right after the start of flow reversal are also discussed in detail. Moreover, the non-dimensional time leads of the horizontal velocities at different heights in the boundary layer over the free-stream velocity are evidenced to be more noticeable toward the bottom, and also in lower ratio of wave height to water depth. A similarity profile for the non-dimensional time lead versus the non-dimensional height above the bottom surface is also presented.

  • 38. Lin, Chang
    et al.
    Hsieh, SC
    Lo, LF
    Chang, SY
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Green aerator using periodically oscillatory flow generated inside a vertical dropping pool2012Conference paper (Refereed)
    Abstract [en]

    The flow conditions for generating periodically oscillatory flows and thus entraining a large amount of air bubbles into the water mass in a vertical dropping pool, which can be used potentially as a green aerator, were investigated experimentally. The approaching flows passing through upstream reach of a vertical dropping pool were studied under sub-critical condition. A wave gauge was used to measure the free surface fluctuations in the pool, and flow visualization technique was employed to reveal the flow structure of the dropping flows qualitatively. Under certain conditions, the falling flow over a vertical dropping pool forms a switching jet that oscillates up and down periodically and impinges on the bottom and the downstream corner of the pool alternately. The switching jet switches between an impinging jet (or napped flow) and a sliding jet (or skimming flow), causing it to oscillate periodically with a unique period and to entrain a large number of air bubbles into the switching jet, thus enhancing the dissolved oxygen quantity and turbulent mixing. The primary frequency of the periodic oscillation was determined by applying spectral analysis to the time history of wave-gauge measurements for the free surface elevation of the dropping flows. Variables influencing the fundamental oscillation frequency were carefully checked, and an empirical relation between a weighted Strouhal number and a grouped non-dimensional parameter was proposed to predict the primary frequency of the periodically oscillatory flow.

  • 39. Lin, Chang
    et al.
    Kao, MJ
    Tzing, GW
    Wong, WY
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Study on Flow Fields of Boundary-Layer Separation and Hydraulic Jump during Rundown Motion of Shoaling Solitary Wave2015In: Journal of Earthquake and Tsunami, ISSN 1793-7116, Vol. 9, no 5Article in journal (Refereed)
    Abstract [en]

    The characteristics of flow fields for a complete evolution of the non-breaking solitary wave, having a wave-height to water-depth ratio of 0.363 and propagating over a 1:5 sloping bottom, are investigated experimentally. This study mainly focuses on the occurrences of both flow separation on the boundary layer under an adverse pressure gradient and subsequent hydraulic jump with the abrupt rising of free surface during run-down motion of the shoaling wave, together with emphasis on the evolution of vortex structures underlying the separated shear layer and hydraulic jump. A flow visualization technique with particle trajectory method and a high-speed particle image velocimetry (HSPIV) system with a high-speed digital camera were used. Based on the instantaneous flow images visualized and/or the ensemble-averaged velocity fields measured, the following interesting features, which are unknown up to date, are presented and discussed in this study: (1) Flow bifurcation occurring on both offshore and onshore sides of the explicit demarcation curve and the stagnation point during run-up motion; (2) The dependence of the diffuser-like flow field, being changed from the supercritical flow in the shallower region to the subcritical flow in the deeper counterpart, on the Froude number during the early and middle stages of run-down motion; (3) The positions and times for the occurrences of the incipient flow separation and the sudden rising of free surface of the hydraulic jump; (4) The associated movement and evolution of vortex structures under the separated shear layer, the hydraulic jump and/or the high-speed external main stream of the retreated flow; and (5) The entrainment of air bubbles from the free surface into the external main stream of the retreated flow.

  • 40. Lin, Chang
    et al.
    Liu, Ting
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Lu, Chia-Hsun
    Visualizing Conduit Flows around Solitary Air Pockets2014In: Journal of engineering mechanics, ISSN 0733-9399, E-ISSN 1943-7889, Vol. 141, no 5Article in journal (Refereed)
    Abstract [en]

    Understanding flow characteristics around air pockets is fundamental in the study of air entrainment and transport in pipelines. This study deals with the use of flow visualization technique (FVT) and high-speed particle image velocimetry (HSPIV) in exploration of the characteristics around stationary air pockets in horizontal-pipe flow. The air-pocket volume varies from 0 to 10.0 mL, and the air pocket is injected into a fully developed turbulent flow with Reynolds numbers between 17,000 and 18,400. In the plane of symmetry, the main flow features include (1) a horseshoe vortex upstream, (2) a stagnation point on the frontal interface, (3) a separation point and a separated shear layer beneath, (4) a reattached shear layer downstream of the reattachment point (for air-pocket volumes greater than 2.0 mL), and (5) a reverse-flow region downstream. The deformable air pocket in the turbulent flow causes streamwise random movements of both the stagnation and separation points around their mean positions. The flow pattern is categorized based on the occurrence of either separated flow or flow reattachment. Fully separated flow (Mode I) occurs at air-pocket volumes less than 2.0 mL. Intermittently reattached flow (Mode II) occurs if the volume is within 2.0–5.0 mL. Fully reattached flow (Mode III) is evident at volumes greater than 5.0 mL. Water particles on the air-pocket surface move with the adjacent flow, thus forming a slip boundary. The evolution of mean streamwise velocity beneath the air pocket demonstrates the formation of either a separated or a reattached shear layer. Using nonlinear regression analysis, appropriate characteristic velocity and length scales are determined to obtain similarity profiles in the separated shear layer beneath.

  • 41. Lin, Chang
    et al.
    Lu, CH
    Liu, Ting
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Characteristics of air-water interface of air pockets in a conduit2014Conference paper (Refereed)
    Abstract [en]

    The presence of air pockets in a pipeline system often causes reduction in its efficiency and shortens its service life. Potential safety hazards arise in some cases from air blowout or blowback. It is thus of interest to examine the water flow field at air pockets and the feature of water-air interface. This study applied flow visualization technique and high-speed particle image velocimetry (HSPIV) to investigate characteristics of flow fields at stationary solitary air pockets in a fully-developed horizontal pipe flow. Experiments were performed in a Plexiglas pipe having an inner diameter of 9.6 cm, with Titanium dioxide powder as tracer for measurements. The results show that a horseshoe vortex and reverse flow pattern existed both up- and downstream of the air pockets. A deformable air pocket in the turbulent flow caused streamwisely a random movement of both stagnation and separation points around their mean positions. An intermittent flow re-attachment occurred also downstream of the mean separation point. The air-water interface was not stationary but moved with the adjacent water flow.

  • 42. Lindblom, E.
    et al.
    Arnell, M.
    Flores-Alsina, X.
    Stenström, F.
    Gustavsson, D. J. I.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Jeppsson, U.
    Dynamic modelling of nitrous oxide emissions from three Swedish sludge liquor treatment systems2016In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 73, no 4, p. 798-806Article in journal (Refereed)
    Abstract [en]

    The objective of this paper is to model the dynamics and validate the results of nitrous oxide (N2O) emissions from three Swedish nitrifying/denitrifying, nitritation and anammox systems treating real anaerobic digester sludge liquor. The Activated Sludge Model No. 1 is extended to describe N2O production by both heterotrophic and autotrophic denitrification. In addition, mass transfer equations are implemented to characterize the dynamics of N2O in the water and the gas phases. The biochemical model is simulated and validated for two hydraulic patterns: (1) a sequencing batch reactor; and (2) a moving-bed biofilm reactor. Results show that the calibrated model is partly capable of reproducing the behaviour of N2O as well as the nitritation/nitrification/denitrification dynamics. However, the results emphasize that additional work is required before N2O emissions from sludge liquor treatment plants can be generally predicted with high certainty by simulations. Continued efforts should focus on determining the switching conditions for different N2O formation pathways and, if full-scale data are used, more detailed modelling of the measurement devices might improve the conclusions that can be drawn.

  • 43.
    Liu, Ting
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Modelling air―water flows in bottom outlets of dams2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    If air is entrained in a bottom outlet of a dam in an uncontrolled way, the resulting air pockets may cause problems such as blowback, blowout and loss of discharge capacity. In order to provide guidance for bottom outlet design and operation, this study examines how governing parameters affect air entrainment, air-pocket transport and de-aeration and the surrounding flow structure in pipe flows. Both experimental and numerical approaches are used.

    Air can be entrained into the bottom outlet conduit due to vortex formation at the intake if the intake submergence is not sufficient. The influent of the intake entrance profiles and channel width on the critical submergence were studied in the experiment.

    The experimental study was performed to investigate the incipient motion of air pockets in pipes with rectangular and circular cross sections. The critical velocity is dependent on pipe slope, pipe diameter, pipe roughness and air-pocket volume. If the pipe is horizontal, air removal is generally easier in a rectangular pipe than in a circular pipe. However, if the pipe is downward-inclined, air removal is easier in a circular pipe.

    When a bottom outlet gate opens, air can become entrained into the conduit in the gate shaft downstream of the gate. Using FLUENT software, the transient process of air entrainment into a prototype bottom outlet during gate opening is simulated in three dimensions. The simulations show in the flow-pattern changes in the conduit and the amount of air entrainment in the gate shaft. The initial conduit water level affects the degree of air entrainment. A de-aeration chamber is effective in reducing water surface fluctuations at blowout.

    High-speed particle image velocimetry (HSPIV) were applied to investigate the characteristics of the flow field around a stationary air pocket in a fully developed horizontal pipe flow. The air pocket generates a horseshoe vortex upstream and a reverse flow downstream. A shear layer forms from the separation point. Flow reattachment is observed for large air pockets. The air―water interface moves with the adjacent flow. A similarity profile is obtained for the mean streamwise velocity in the shear layer beneath the air pocket.

  • 44.
    Liu, Ting
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Air-pocket movement in an 18.2 degree downward 240 mm conduit, experimental studies2012In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 28, p. 791-795Article in journal (Refereed)
    Abstract [en]

    Experiments are carried out in a test rig, consisting of a Plexiglas pipe with an inner diameter of 240 mm and an inclination of 18.2o, to investigate air-water two-phase flows in conjunction with bottom spillways. Results show that the critical velocity, which is the minimal water velocity to start moving an air pocket, in the rough pipe, is independent of the air-pocket volume; in the smooth pipe it doesn’t increase with increasing diameter as much as the previous researchers indicated. Pipe roughness doesn’t affect the velocity of the air-pocket when it moves upstream in the downward inclined pipe.

  • 45.
    Liu, Ting
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Three-Dimensional Computations Of Water-Air Flow In A Bottom Spillway During Gate Opening2014In: Engineering Applications of Computational Fluid Mechanics, ISSN 1994-2060, E-ISSN 1997-003X, Vol. 8, no 1, p. 104-115Article in journal (Refereed)
    Abstract [en]

    Undesired entrainment of air in a bottom spillway often leads to problems in both safety and operational functions. A numerical analysis of a transient process of air entrainment into bottom spillway flows when a spillway gate is opened was conducted in this study. The Volume of Fluid (VOF) model was used. The 3D computational domain consisted of a spillway conduit, a moving bulkhead gate, a gate shaft, an upstream reservoir and a downstream outlet. The large number of cells, together with the dynamic mesh modelling of the moving gate, required substantial computational resources, which necessitated parallel computing on a mainframe computer. The simulations captured the changes in the flow patterns and predicted the amount of air entrainment in the gate shaft and the detrainment downstream, which help in the understanding of the system behaviour during opening of the spillway gate. The initial conduit water level and the gate opening procedure affect the degree of air entrainment in the gate shaft. To release the undesired air, a de-aeration chamber with a tube leading to the atmosphere was added to the conduit. Despite the incomplete air release, the de-aeration chamber was found to be effective in reducing water surface fluctuations in the downstream outlet.

  • 46.
    Llorens del Pino, Alba
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Diversion of water from a tailings dam: Spillway arrangement and spillway channel designed to be maintenance free for 1000 years2007Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    An elaboration on how to construct a spillway for closure for a large tailings pond completely enclosed by embankments, leading to a situation where construction in bedrock is not possible is presented with the following conclusion. A stepped spillway arrangement constructed with granite blocks will require of large blocks for being stable, and will require of filters that are not always considered functional in long-term perspective. It is presented an analysis of the overall stability of the structure proposed and of the stability of its individual blocks.  In addition, it will be impossible to design a vegetated channel that remains stable, without silting and without erosion, over thousand years without maintenance.

  • 47. Lundell, Dan
    et al.
    Jin, Feng
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Some aspects of rock-filled concrete in hydraulic structures2011Conference paper (Refereed)
    Abstract [en]

    The study addresses several aspects of Rock-Filled Concrete (RFC) – a new construction material developed for use in hydraulic structures. Some of the latest results of compressive strength, tensile strength and compaction level of the material are presented. In RFC, Self-Compacting Concrete (SCC) is used together with large aggregates (minimum of 30 cm in size), to produce concrete with a high content of aggregate material and a low content of cement. The large aggregates in RFC complicate the material testing. In this study, the aggregate size is limited to 150 mm in size and the strength parameters have been evaluated using cubic samples with a surface area of 500 * 500 mm. The results imply that RFC does not lead to reduced material strength as compared to SCC. Based on the latest performance results of the material, together with results from earlier studies of the production costs and environmental impacts of RFC, the conclusion is that RFC has advantages of lower material cost, faster construction and less environmental impacts as compared to both conventional concrete (CC) and Roller-Compacted Concrete (RCC) when used in large concrete structures such as dams.

  • 48. Mazzoleni, M.
    et al.
    Dottori, F.
    Brandimarte, Luigia
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Tekle, S.
    Martina, M. L. V.
    Effects of levee cover strength on flood mapping in the case of levee breach due to overtopping2017In: Hydrological Sciences Journal, ISSN 0262-6667, E-ISSN 2150-3435, Vol. 62, no 6, p. 892-910Article in journal (Refereed)
    Abstract [en]

    The reliability of a levee system is a crucial factor in flood risk management. In this study we present a probabilistic methodology to assess the effects of levee cover strength on levee failure probability, triggering time, flood propagation and consequent impacts on population and assets. A method for determining fragility curves is used in combination with the results of a one-dimensional hydrodynamic model to estimate the conditional probability of levee failure in each river section. Then, a levee breach model is applied to calculate the possible flood hydrographs, and for each breach scenario a two-dimensional hydrodynamic model is used to estimate flood hazard (flood extent and timing, maximum water depths) and flood impacts (economic damage and affected population) in the areas at risk along the river reach. We show an application for levee overtopping and different flood scenarios for a 98 km reach of the lower Po River in Italy. The results show how different design solutions for the levee cover can influence the probability of levee failure and the consequent flood scenarios. In particular, good grass cover strength can significantly delay levee failure and reduce maximum flood depths in the flood-prone areas, thus helping the implementation of flood risk management actions.

  • 49.
    Molinder, Gabriella
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Internal erosion in the pervious foundation of an embankment dam: A case study on the Lossen dam2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Lossen dam is an embankment dam in the Swedish river Ljusnan. The dam is founded on thick layers of stratified glaciofluvial sediments and till. Ever since construction, there have been problems with high pore pressures, large seepage flows and springs downstream of the right part of the dam. After the first filling of the reservoir, a large drainage trench was constructed downstream of the dam to lower pore pressures. Sinkholes and settlements downstream of the dam have occurred repeatedly over the lifetime of the dam, particularly in the area surrounding the large drainage trench.

    This study aims to investigate the causes of the sinkholes and assess the risks of internal erosion in the foundation and in the soil downstream of the dam.

    A model of the groundwater flow has been created in Visual MODFLOW. Calculations for assessing the soils susceptibility for contact erosion and suffusion have been performed, using soil gradation curves (both from the 1960s and from new samples).

    The results from the erosion calculations show that the probability of contact erosion being the sole cause of the internal erosion is minor. However, a majority of the soil samples tested are internally unstable (susceptible for suffusion). The possibility of backward erosion piping can not be dismissed but would need further investigation in order to be properly assessed.

    Due to the very heterogeneous structure of the soil in the area downstream of the dam, it is hard to predict the extent of the eroding soil layers and, thus, the future development of the erosion.

    A conclusion is that the soil downstream of the dam is subject to internal erosion, which is also the cause of the observed sinkholes and settlements. The internal erosion is probably not a threat to dam safety at the moment, but can possibly evolve as a problem in the future. Therefore close monitoring of the changes in seepage patterns and sediment transport is recommended. Possible solutions to stop the erosion include extending the drainage system with more pressure relief wells, and placing a filter blanket in the seepage exit area. 

  • 50.
    Morén, Ida
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Riml, Joakim
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Design of Remediation Actions for Nutrient Mitigation in the Hyporheic Zone2017In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 53, no 11, p. 8872-8899Article in journal (Refereed)
    Abstract [en]

    Although hyporheic exchange has been shown to be of great importance for the overall water quality of streams, it is rarely considered quantitatively in stream remediation projects. A main driver of hyporheic exchange is the hydraulic head fluctuation along the streambed, which can be enhanced by modifications of the streambed topography. Here we present an analytical 2-D spectral subsurface flow model to estimate the hyporheic exchange associated with streambed topographies over a wide range of spatial scales; a model that was validated using tracer-test-results and measurements of hydraulic conductivity. Specifically, engineered steps in the stream were shown to induce a larger hyporheic exchange velocity and shorter hyporheic residence times compared to the observed topography in Tullstorps Brook, Sweden. Hyporheic properties were used to parameterize a longitudinal transport model that accounted for reactions in terms of first-order decay and instantaneous adsorption. Theoretical analyses of the mitigation effect for nitrate due to denitrification in the hyporheic zone show that there is a Damkohler number of the hyporheic zone, associated with several different stream geomorphologies, that optimizes nitrate mass removal on stream reach scale. This optimum can be limited by the available hydraulic head gradient given by the slope of the stream and the geological constraints of the streambed. The model illustrates the complex interactions between design strategies for nutrient mitigation, hyporheic flow patterns, and stream biogeochemistry and highlights the importance to diagnose a stream prior remediation, specifically to evaluate if remediation targets are transport or reaction controlled.

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