Change search
Refine search result
12 1 - 50 of 88
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1. Admass, M.
    et al.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    3D numerical modelling of flow and sediment transport in rivers2007In: International Journal of Sediment Research, ISSN 1001-6279, Vol. 22, no 2, p. 168-174Article in journal (Refereed)
  • 2.
    Alderman, Carin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Andersson, Sophia
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Cavitation assessment of the Baihetan discharge tunnel – Using Computational Fluid Dynamics2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Recently it has become more common in the construction of large dams to reuse diversion tunnels as flood discharge tunnels in the final structure. These tunnels handle large flows with the characteristics of open channel flow. When such large hydrological forces act upon a structure there are several problems to be expected. One of these is the occurrence of cavitation, which could have potential hazardous erosion as a consequence. Cavitation is the formation and collapse of bubbles that create a shockwave strong enough to erode the underlying material.

    The Baihetan dam is one of the largest hydro power projects in China at present. It has three discharge tunnels that all run the risk of developing cavitation damages. By modelling one of the tunnels using Computational Fluid Dynamics (CFD) it is possible to investigate where in the tunnel structure cavitation is likely to occur.

    This degree project assesses the risk of cavitation erosion in the Baihetan tunnel using the static pressure distribution, the velocity distribution and modern cavitation theory. Several modifications of the tunnel – including alterations in the gradient and construction parameters – are simulated in order to investigate if changes in the design can mitigate the cavitation problem. None of the analysed modifications completely eliminate the problem and aeration is recommended to counteract the problem. This study indicates where cavitation might be a problem in the Baihetan tunnel and can be used as a basis for further research.

  • 3.
    Axelsson, Johan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Knutsson, Roger
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Numerical modeling of a slotted flip bucket spillway system – The Shibuya Hydropower Project. 2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    CFD is today a big part of the design process in hydraulic engineering and is more economical and time efficient than traditional scale models. But, there are still issues concerning the agreement with scale models in large and complex geometries.

    In this degree project a high head, five channeled, slotted flip bucket spillway system is analyzed with the CFD software FLUENT and compared with existing scale model results.

    The sought hydraulic parameters in each channel were the discharge capacity, the pressure distribution and the throw distance from the flip buckets.

    The discharge capacity and pressure distribution was practically equal for all five channels and only the throw distance from Channel 1 deviated from the others. The agreement with data from the scale model is quite low.

    The biggest error sources behind the bad agreement may depend on the lack of computational power which led to bad choice of cell size, model delimitations and simplifications.

    CFD models can easily be built up by people without experience in hydraulics which can lead to fatal errors when building up the model and interpreting results. Hence, long experience in CFD or verification of the numerical results with several different hydraulic parameters is the only way to guarantee qualitative results from CFD modeling.

  • 4.
    Basirat, Farzad
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    CO2 leakage in a Geological Carbon Sequestration system: Scenario development and analysis.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this project was to study the leakage of CO2 in a Geological Carbon Sequestration (GCS) system. To define the GCS system, a tool that is known as an FEP database was used. FEPs are the features, processes and events that develop scenarios for the goal of the study. Combinations of these FEPs can produce thousands of scenarios. However, among all of these scenarios, some are more important than others for leakage. The FEPs that were used as scenario developers were the formation of the liquid flow, the salinity of the formation liquid, diffusion as a process for gas bubble transport and the depth of the reservoir layer. In this study, the leakage path is considered as the presence of a fracture in sealed caprock. The fractures can be modeled using various approaches. Here, I represented the influence of fracture modeling by applying the Equivalent Continuum Method (ECM) and the Dual-Porosity and Multi-continuum methods to leakage. This study suggests that considering groundwater in the aquifer would reduce the leakage of CO2 and that a shallower formation leads to higher leakage. This study can be expanded to future studies by including external FEPs that are related to the FEPs that were used in this study.

  • 5.
    Boberg, Björn
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Holm, David
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    FEM modeling of concrete gravity dams.2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 6.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Flow characteristics of bottom outlets with moving gates2010In: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 48, no 4, p. 476-482Article in journal (Refereed)
    Abstract [en]

    This study investigates the discharge characteristics of a bottom outlet with a moving gate by Flow3D. Experimental results for a scale model outlet of the Aswan Dam, Egypt, were used. Two different flow features were found. Pressurized flow established if the flume was filled and then the gate was slowly opened. However, a free surface flow occurred if the gate was fully opened and the entire flume was slowly flooded with water. The numerical simulations successfully captured the two flow patterns as well as the discharges and water surface profiles. The discharges were predicted with sufficient accuracy using the first-order momentum advection scheme. In comparison with the k-epsilon turbulence model, the Re-Normalization Group model yields the best agreement with the experiments. The model performed with similar accuracy for both model and prototype cases.

  • 7.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Hydraulic Engineering (moved 20130630).
    Reservoir sedimentation2012In: Encyclopedia of Earth Sciences Series, Springer Netherlands, 2012, p. 628-649Chapter in book (Refereed)
  • 8.
    Dargahi, Bijan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Setegn, Shimelis Gebriye
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Combined 3D Hydrodynamic and Watershed Modelling of Lake Tana, Ethiopia2011In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 398, no 1-2, p. 44-64Article in journal (Refereed)
    Abstract [en]

     The growing high demand for lake Tana water portends a disturbing future. The main objective of this paper is to make a contribution to the development of a sustainable use of the water of Lake Tana. A fully three-dimensional hydrodynamic model was combined with a watershed model and together, these models were successfully validated for the year 2006. The flow structure is characterized by large recirculation and secondary flow regions. Secondary flows are induced by hydrodynamic instabilities occurring at the interfaces of layers with a velocity gradient and the interaction with the irregularities of the bed. The weak stratification process in Lake Tana is characterized by a classic summer profile, which is more pronounced during January-February. Mixing processes in the lake are controlled by wind, the mixing energy induced by both river inflows and the lake outlet, and convective mixing due to the negative buoyancy. An alarming fall of the water levels in Lake Tana was found in response to the planned water withdrawal. The long flushing time (19 months) will not allow a fast decay of contaminated materials released into the lake. The flow structure will not be significantly modified by the planned water withdrawal but the flushing time will decrease. The hydrodynamics of Lake Tana resemble a closed system similar to a shallow reservoir with an overflow type outlet. The implication is that the lake is vulnerable to changes in external conditions and sustainable use of the water resource of the lake will require awareness of this vulnerability. The combined watershed and hydrodynamic models would be effective tools to achieve this awareness. It is also necessary to address the impact of climate change on the fate of the lake. These are all difficult challenges that need to be addressed to safeguard the sensitive eco-system of the area.

  • 9.
    Henkel, Herbert
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Piazolo, Sandra
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Jing, Lanru
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Engineering Geology and Geophysics.
    A deep rock laboratory in the Dellen impact crater2010In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 132, no 1, p. 45-54Article in journal (Refereed)
    Abstract [en]

    The Deep Rock Lab is a platform to establish a comprehensive subsurface bedrock characterization approach, by integrating site characterization techniques applied from different disciplines of geo-mechanics, geochemistry, hydrogeology, structural geology, lithology and geophysics, with consideration of the effects of coupled geological processes of importance for the understanding of groundwater renewal, continental shield deformations, engineering issues related to geological disposal of nuclear waste and CO2, and geothermal energy retrieval in crystalline rocks. The approach will focus on the physics and chemistry of crystalline rocks and groundwater with down-the-hole measurements of relevant variables, using and developing more efficient geo-scientific site investigation techniques for deep boreholes at a chosen site, and develop more advanced down-the-hole measurements and numerical modelling methods with more advanced inversion algorithms to help integrate data interpretations and object representations. The goal is to develop this platform into a long-term research facility that can be readily used by the scientific community for both subsurface fundamental and engineering-oriented research. Such a platform will be especially important for the education of PhD students for generations to come. The integrated drilling and research facility is suggested to be located at the Dellen site. This site has an impact crater with a large range of expected physical property changes with depth, complex and multiple thermal processes that have affected the bedrock, a favorable infrastructure and local supporting activities, and a large body of existing geo-scientific data.

  • 10. Hoedl, Iris
    et al.
    Hoedl, Josef
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Singer, Gabriel
    Besemer, Katharina
    Battin, Tom J.
    Voronoi Tessellation Captures Very Early Clustering of Single Primary Cells as Induced by Interactions in Nascent Biofilms2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 10, p. e26368-Article in journal (Refereed)
    Abstract [en]

    Biofilms dominate microbial life in numerous aquatic ecosystems, and in engineered and medical systems, as well. The formation of biofilms is initiated by single primary cells colonizing surfaces from the bulk liquid. The next steps from primary cells towards the first cell clusters as the initial step of biofilm formation remain relatively poorly studied. Clonal growth and random migration of primary cells are traditionally considered as the dominant processes leading to organized microcolonies in laboratory grown monocultures. Using Voronoi tessellation, we show that the spatial distribution of primary cells colonizing initially sterile surfaces from natural streamwater community deviates from uniform randomness already during the very early colonisation. The deviation from uniform randomness increased with colonisation - despite the absence of cell reproduction - and was even more pronounced when the flow of water above biofilms was multidirectional and shear stress elevated. We propose a simple mechanistic model that captures interactions, such as cell-to-cell signalling or chemical surface conditioning, to simulate the observed distribution patterns. Model predictions match empirical observations reasonably well, highlighting the role of biotic interactions even already during very early biofilm formation despite few and distant cells. The transition from single primary cells to clustering accelerated by biotic interactions rather than by reproduction may be particularly advantageous in harsh environments - the rule rather than the exception outside the laboratory.

  • 11.
    Holmbom, Joakim
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Modelling of Waves and Currents in the Baltic Sea.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    To facilitate the process of setting up small scale environmental models in coastal and offshore areas a wave model and a 2D current model for the Baltic Sea have been set up with MIKE 21. The ambition is that the Baltic Sea model can serve as a source of boundary conditions for local models.

    The main focus in the project has been to determine which input data to use to get the best results and then to calibrate and validate the model with the best data sets available.

    The wave model has been tested with three different sources of wind forcing and the results with the different sources are evaluated.

    The wave model has been calibrated and validated against five wave buoys and the current model against three current observation stations. The comparison shows that the wave model gives good estimations of wave height, period and direction. The output of the current model coincides with observations where distinct current patterns exist. The wave model is considered a good source to extract wave statistics from for the entire Baltic Sea. The current model can be used for scenarios or areas that do not suffer from the limitations of a 2D model.

  • 12.
    Jonsson, Karin
    et al.
    Department of Earth Sciences, Uppsala University.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Influence of Hyporheic Exchange on Solute Transport in a Highly Hydropower-Regulated River2005In: Water Quality Hazards and Dispersion of Pollutants / [ed] Czernusznko W., Rowinski P.M., Springer-Verlag New York, 2005, p. 185-213Chapter in book (Refereed)
  • 13.
    Jonsson, Stefan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Avrinning från körbanor och hydrauliken hos stenfyllda dagvattendiken.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The purpose of this work is to describe the hydraulics in rock-filled stormwater ditches and surface runoff from roadways, and to make a statement about the degree of purification based on other research. There has been no research in either impact or cost savings / higher expenses by using this type of system compared to a conventional stormwater systems for motorways. If this type of solution is cost effective it would mean savings for future construction in which this solution is chosen. A comparison was made of how well the calculations based on P90, which were used during the design stage with the upcoming P104. P90 and P104 is published by the interest association Swedish water and can be viewed as guidelines for water and wastewater industry how to make the design of stormwater systems. For a rainfall of 10-years return period and a 10-minutes duration, the precipitation will increase 4%, according to the model used in the P104 compared to P90. If the intensity and duration curves are plotted using rainfall data from Uppsala, it will increase the precipitation 24% compared to P90. Increases between P90 and P104 will not exceed the capacity of the reservoirs since the increase is so small. If these models are inaccurate and precipitation intensity will be equal to the intensity and duration curves, the capacity of the reservoirs will be exceeded. However, as the studies indicate that the water does not take the way that have been adopted in designing and normally assumed by stormwater projections of this kind. It is likely that most of the precipitation that falls will never reach the ditches and infiltrate into these. For small amounts of precipitation, the majority of the water will infiltrate in the support strip near the edge of the asphalt. If there are large amounts of rainfall the recharge capacity of the support strip will be exceeded, then the surface water will infiltrate in the upper trench slope. Precipitation that infiltrates through the support strip will be percolating down through the soil with an essentially vertical gradient, but some of the water will be transported horizontally into the road structure. The precipitation that enters the road structure will be led to the collector pipes via fiber cloth in the bottom of the embankment. There is a risk that the water that enters the embankment causes damage to the road. Various injuries that can occur are: reduced friction between the grains in the unbound filling materials, redistribution of loads, pumping, depressions, increased cracking of the carriageway and damage that may occur when freezing during the cold season. Even if the water does not go through the stone-filled stormwater ditches, the cleaning effect will not be lost, purification will take place in the road structure and probably be at least as high as it had been if the precipitation took the way that it was designed for. It could be so that the ditches will have no other effect than sinks for ground water and safe running off surfaces. According to the contractor the cost savings were about 15% compared to a conventional stormwater systems. This figure is probably on the low side when Ramboll came in late in the projection and had to redo parts of the design of the system during construction time.

  • 14. Klos, Ryk
    et al.
    Shaw, George
    Xu, Shulan
    Dverstorp, Björn
    Nordén, Maria
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Potential for high transient doses due to accumulation and chemical zonation of long-lived radionuclides across the geosphere-biosphere interface2011In: Radioprotection - Revue de la Societé Francaise de Radioprotection, ISSN 0033-8451, E-ISSN 1769-700X, Vol. 46, no 6, p. S453-S459Article in journal (Refereed)
    Abstract [en]

    Planning for the disposal of spent nuclear fuel is at an advanced stage in several nations around the world. Licensing of the disposal facility requires correspondingly detailed assessment of the future performance of the facility. With increased site-specific detail available to the assessment, local characteristics play an increasingly important role in determining the potential radiological risk posed by releases to the biosphere. In this paper we go beyond existing reference biosphere models and investigate the potential for specific accumulation mechanisms. The implications for the modelling carried out in long timescale performance assessment are discussed.

  • 15.
    Liu, Ting
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Air-pocket transport in conjunction with bottom-outlet conduits for dams2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Undesired air entrainment in bottom outlet conduits of dams may cause pressure transients, leading to conduit vibrations, blowback, discharge pulsation and even cavitation, and jeopardize the operational safety. Due to design limitations or construction costs, it is impossible to create an air free environment in a pressurized pipe. Therefore, it is essential to understand the air transport in enclosed pipes in order to provide guidance in bottom outlet design and operation. The commonly used criterion of the air-pocket movement in pipe flow is the water flow velocity for starting moving an air pocket, the so-called critical velocity.

    In this thesis, the classical Volume of Fluid (VOF) model combined with the k-ε turbulence model is adopted for the computation of the critical velocity of a 150-mm pipe. The computed critical velocities are compared with the experimental results. The governing parameters investigated in this study include pipe slope and diameter, wall shear stress and air-pocket volume. Meanwhile, the carrying capacity (air-pocket velocity/ flow velocity) at all pipe slopes are analyzed. The simulation results of air pockets with different volumes in the bottom outlet conduit of Letten Dam in Sweden are presented in this study.

    Moreover, experimental study was conducted to measure the critical velocity for a 240-mm Plexiglas pipe. The results are in agreement with the experiments performed by HR Wallingford (HRW) in 2003 in terms of the effects of pipe slope and air-pocket volume; however, the critical Froude pipe number is slightly smaller in this study. In rough pipes, a larger critical velocity is required compared with that in the smooth pipe. The removal mechanism in the rough pipe involves the successive loss of air caused by turbulence. This explains that the air-pocket size, with the dimensionless air-pocket volume n < 0.015, has little impact on the critical velocity for the rough pipe. In addition, roughness has little impact on the air-pocket velocity when it moves upstream in the downward inclined pipe. The trapped air bubbles most likely remain permanently in the rough pipe.

  • 16.
    Liu, Ting
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    CFD Modeling of Air Pocket Transport in Conjunction with Spillway Conduits2011In: 11th International Conferenceon Fluid Control, Measutements and Visualization, Keeling, Taiwan, December 2-9 2011, 2011Conference paper (Refereed)
    Abstract [en]

    This paper focuses on simulations of enclosed air pocket movements in conjunction with bottom outlet operations. The critical velocity of water for air pocket transport in pipe is the minimal flow velocity for the air pocket start to move downstream. A numerical model is developed to simulate the critical velocity of air pocket transport in pipe flow and to discuss the impacts of tunnel slope, size of the air pocket and wall roughness. The computations are performed in FLUENT using Volume of Fraction (VOF) model combined with k-epsilon model. Parallel computing is adopted for high computational performance.

    The modeled critical velocity is compared with experimental results and they increase with increasing slopes. However, as the roughness height defined in the model is not big enough to represent the reality and no wall shear stress is applied in the upper wall where air pocket and wall contact, the modeled critical velocity is smaller than the experimental ones. Therefore, wall roughness contributes to keep the air pocket from moving downstream which is important in modeling critical velocity. However, by assuming a constant wall shear stress for the air phase the same as the water phase will overestimate the shear stress on the air pocket.

    Two air pocket volumes are simulated at the slope 0.8 degrees which shows the bigger the air pocket is the higher the critical velocity is. Modeling results also show that the critical velocity is non-zero in horizontal pipe and there is a limit for the carrying capacity at all slopes. The simulations of air pockets with different volumes in the bottom tunnel of Letten dam in North of Sweden is shown in this paper as well.

  • 17.
    Liu, Ting
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Experimental studies of air pocket movement in a pressurized spillway conduit2013In: Journal of Hydraulic Research, ISSN 0022-1686, E-ISSN 1814-2079, Vol. 51, no 3, p. 265-272Article in journal (Refereed)
    Abstract [en]

    Undesired air entrainment in a bottom outlet conduit causes pressure transients, leading to conduit vibrations, blowbacks and discharge pulsations and thus endangers operational safety. In this study, the propagation velocity of a solitary air pocket and the characteristics of its critical velocity were examined in experiments conducted using a 240-mm-diameter pipe. Air pocket movement depends on the pipe diameter, slope, roughness and air pocket size. The critical pipe Froude number for initiating downstream movement of an air pocket is smaller in a larger pipe, most likely due to the scale effect and/or to a smaller reduction in the effective cross-sectional area. The critical velocity in rough pipes was found to be independent of the air pocket size. A minimum Froude number was suggested for a rough pipe instead of a critical pipe Froude number because the air removal process was found to involve successive air losses from the air pocket caused by turbulence.

  • 18.
    Liu, Ting
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Experiments of Air-pocket Movement in an 18.2 degrees downward 240-mm Conduit2012In: 2012 International Conference On Modern Hydraulic Engineering, Elsevier, 2012, p. 791-795Conference paper (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.

  • 19.
    Liu, Ting
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Hydraulic Engineering (moved 20130630).
    Yang, James
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Hydraulic Engineering (moved 20130630).
    Incipient motion of solitary air pockets in a rectangular pipe2013In: Journal of Applied Water Engineering and Research, ISSN 2324-9676, E-ISSN 2324-9676, Vol. 1, no 1, p. 58-68Article in journal (Refereed)
    Abstract [en]

    The operation of bottom-outlet gates often gives rise to entrained air in the form of air pockets in the conduit under full-flow conditions. If unexpectedly released, it would cause problems for both personnel security and operational function. The present study addresses, through experimentation, the incipient movement of solitary air pockets in a rectangular pipe. A horizontal pipe and a 9.6° downward-inclined pipe are examined. The cross-section of the pipe measures 200 mm (width) by 250 mm (height). As distinct from a circular pipe, an air pocket in the rectangular pipe exhibits, at its incipient motion, a shape that depends mainly on factors such as the sloping angle of the pipe, cross-sectional location of the air pocket and its volume. These factors also determine the critical velocity of the air pocket. The experiments have shown that only small air pockets can exist under the roof. The corner is a cross-sectionally equilibrium position for larger air pockets. The air pocket in the corner position takes the shape of an elongated rectangular prism in the horizontal pipe and a triangular prism in the sloping one. When compared with a circular pipe, the critical velocity of air pockets in the rectangular pipe is lower if the pipe is horizontal and higher if it has a downward inclination.

  • 20. Marklund, L.
    et al.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Xu, S.
    Dverstorp, B.
    The effect of topography and quaternary deposits on circulation of groundwater and discharge area distribution2005In: Proceedings of the 2nd International Conference on Radioactivity in the Environment, 2005, p. 659-662Conference paper (Refereed)
  • 21.
    Marklund, Lars
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Characterisation of discharge areas of radionuclides originating from nuclear waste repositories2008In: Proceedings of the International Conference on Radioecology and Environmental Radioactivity / [ed] Per Strand, Justin Brown and Torun Jolle, 2008Conference paper (Refereed)
  • 22.
    Marklund, Lars
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    The Use of Spectral Analysis to Characterize Topography- Controlled Groundwater FlowManuscript (preprint) (Other academic)
  • 23. Marklund, Lars
    et al.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    The use of spectral analysis-based exact solutions to characterize topography-controlled groundwater flow2011In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 19, no 8, p. 1531-1543Article in journal (Refereed)
    Abstract [en]

    Spectral analysis enhances the ability to analyze groundwater flow at a steady state by separating the top boundary condition into its periodic forms. Specifically, spectral analysis enables comparisons of the impact of individual spatial scales on the total flow field. New exact spectral solutions are presented for analyzing 3D groundwater flow with an arbitrarily shaped top boundary. These solutions account for depth-decaying, anisotropic and layered permeability while utilizing groundwater flux or the phreatic surface as a top boundary condition. Under certain conditions, groundwater flow is controlled by topography. In areas where the groundwater flow is controlled by the topography, the unknown water table is often approximated by the topography. This approximation induces a systematic error. Here, the optimal resolution of digital elevation models (DEMs) is assessed for use as a top boundary in groundwater flow models. According to the analysis, the water-table undulation is smoother than the topography; therefore, there is an upper limit to the resolution of DEMs that should be used to represent the groundwater surface. The ability to represent DEMs of various spectral solutions was compared and the results indicate that the fit is strongly dependent on the number of harmonics in the spectral solution.

  • 24.
    Marklund, Lars
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Topographic and Geological controls of Groundwater Renewal.Manuscript (preprint) (Other academic)
  • 25.
    Marklund, Lars
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
    Xu, S.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Accumulation in the overburden of radionuclides from a leaking nuclear waste repository2008In: American Nuclear Society - 12th International High-Level Radioactive Waste Management Conference 2008, 2008, p. 473-478Conference paper (Refereed)
    Abstract [en]

    The spatial distribution of possible discharge areas of radionuclides originating from repositories of high level radioactive nuclear waste was assessed. This was done by using a 3-D transport model. The results indicate "hot-spots" in the landscape where the radionuclides most likely emerge. These hot-spots are highly related to the hydrological network consisting of streams, lakes and wetlands. The geological factors creating this pattern as well as the characteristics that distinguish these areas from others were investigated. Our result suggests that these hot-spots occur in low elevation areas where the quaternary deposits are significantly greater than the average thickness in the area. The most important factors for the locations of the hot-spots are landscape topography and fracture distribution in the bedrock. As a result of the relationship between, fracture zones, topography and streams, the importance of the topography for the discharge area distribution is not contradicted by the heterogeneity in the bedrock as long as the undulation of the groundwater surface is not extremely small. Due to the similarities within deep groundwater discharge areas, one can make site-specific analyses in one area, which have a broad applicability for migration of radionuclides originating from a nuclear waste repository.

  • 26. McDonnell, J.J.
    et al.
    McGuire, K.
    Aggarwal, P.
    Beven, K.
    Biondi, D.
    Destouni, G.
    Dunn, S.
    James, A.
    Kirchner, J.
    Kraft, P.
    Lyon, S.
    Maloszewski, P.
    Newman, B.
    Pfister, L.
    Rinaldo, A.
    Rodhe, A.
    Sayama, T.
    Seibert, J.
    Solomon, K.
    Soulsby, C.
    Stewart, M.
    Tetzlaff, D.
    Tobin, C.
    Troch, P.
    Weiler, M.
    Western, A.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Wrede, S.
    How old is streamwater?: Open questions in catchment transit time conceptualization, modelling and analysis2010In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 24, no 12, p. 1745-1754Article in journal (Refereed)
    Abstract [en]

    The time water spends travelling subsurface through a catchment to the stream network (i.e. the catchment water transit time) fundamentally describes the storage, flow pathway heterogeneity and sources of water in a catchment. The distribution of transit times reflects how catchments retain and release water and solutes that in turn set biogeochemical conditions and affect contamination release or persistence. Thus, quan- tifying the transit time distribution provides an important constraint on biogeochemical processes and catchment sensitivity to anthropogenic inputs, contamination and land-use change. Although the assumptions and limitations of past and present transit time modelling approaches have been recently reviewed (McGuire and McDonnell, 2006), there remain many fundamental research challenges for understanding how transit time can be used to quantify catchment flow processes and aid in the development and testing of rainfall–runoff models. In this Commen- tary study, we summarize what we think are the open research questions in transit time research. These thoughts come from a 3-day workshop in January 2009 at the International Atomic Energy Agency in Vienna. We attempt to lay out a roadmap for this work for the hydrological commu- nity over the next 10 years. We do this by first defining what we mean (qualitatively and quantitatively) by transit time and then organize our vision around needs in transit time theory, needs in field studies of tran- sit time and needs in rainfall – runoff modelling. Our goal in presenting this material is to encourage widespread use of transit time information in process studies to provide new insights to catchment function and to inform the structural development and testing of hydrologic models.

  • 27.
    Mekonnen, Muluneh Admass
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Modeling flow and sediment transport in water bodies and watersheds2008Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The research focus is on the various modeling aspects of flow and sediment transport in water bodies and watersheds. The interaction of flow with a mobile bed involves a complex process in which various turbulent scales characterized by coherent structures cause a chaotic sediment motion. In many rivers and natural waterways secondary flows that are dominating flow struc-tures bring about more complications. In estuaries and open waterbodies thermal stratification and internal mixing control the flow structure besides the flow interaction with the mobile bed. To adequately model these processes 3D coupled flow and transport models are needed. The research is based on use and adaptation of open source codes for 3D hydrodynamic and sediment transport model known as Estuarine Coastal Ocean Model (ECOMSED) and the Soil and Water Assessment Tool (SWAT) model. A bed load transport model was developed and coupled to ECOMSED. The flow and sediment transport characteristics in a curved channel and a river reach were successfully captured by the model. Improvements in ECOMSED were made to study the effect of wind and basin bathymetry on mixing and flow exchange between two estuaries. Using spectral analysis the hydrological component of SWAT model was investigated for its applicability under limited data conditions in three Ethiopian catchments.

  • 28.
    Mekonnen, Muluneh Admass
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    3D flow and sediment transport modeling in curved channels2007In: 3rd IASTED International Conference on Environmental Modelling and Simulation, EMS 2007: Honolulu, HI: 20 August 2007 through 22 August 2007, 2007, p. 82-87Conference paper (Refereed)
    Abstract [en]

    A 3D hydrodynamic model coupled with a 2D bed load transport model is used to predict flow and sediment transport in a curved channel. The 3D hydrodynamic model is part of ECOMSED (open source code). ECOMSED has a long history of successful applications to oceanic, coastal, and estuarine waters. However, curved channel applications of the code are scarce. Improvements in the advection scheme of momentum and turbulence, and shear stress partitioning were necessary to reproduce realistic and comparable results in a curved channel. To account for the dynamics of the mobile bed boundary, a model for the bed load transport was included in the code. The model reproduced measured secondary currents, bed shear stress distribution, and erosion-deposition patterns on a curved channel.

  • 29.
    Mekonnen,, Muluneh Admass
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Modelling exchange processes between two basins in Stockholm archipelago2007In: Proceedings of the American Water Resource Association 2007 Annual Conference, American Water Works Association, 2007Conference paper (Other academic)
  • 30.
    Mekonnen, Muluneh Admass
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Three dimensional numerical modelling of flow and sediment transport in rivers2007In: International Journal of Sediment Research, ISSN 1001-6279, Vol. 22, no 3, p. 188-198Article in journal (Refereed)
    Abstract [en]

    The 3D numerical model, ECOMSED (open source code), was used to simulate flow and sediment transport in rivers. The model has a long history of successful applications to oceanic, coastal and estuarine waters. Improvements in the advection scheme, treatment of river roughness parameterization and shear stress partitioning were necessary to reproduce realistic and comparable results in a river application. To account for the dynamics of the mobile bed boundary, a model for the bed load transport was included in the code. The model reproduced observed secondary currents, bed shear stress distribution and erosion-deposition patterns on a curved channel. The model also successfully predicted the general flow patterns and sediment transport characteristics of a 1-km long reach of the River Klaralven, located in the north of the county of Varmland, Sweden.

  • 31.
    Mekonnen, Muluneh Admass
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Mixing and exchange processes between two estuaries in Stockholm Archipelago, Sweden2008In: Estuarine, Coastal and Shelf Science, ISSN 0272-7714, E-ISSN 1096-0015Article in journal (Other academic)
    Abstract [en]

    ECOM, a three-dimensional time dependant hydrodynamic and thermodynamic model, was used to investigate the mixing and exchange processes between Farstaviken and Baggensfjärden estu-aries in Stockholm archipelago during April to November 1997. Possible causes of bottom oxy-gen deficiency in the smaller estuary of Farstaviken were also investigated. The model with an additional boundary condition for the sediment-water heat exchange and modifications to reduce the pressure gradient error successfully produced the observed temperature profiles by allowing a time variable reduction in the magnitude of the observed wind speed. In Farstaviken (during stratification periods) the epilimnion region occupies 2.5%-17.5% of the flow depth. The ex-change process between the two smaller and larger estuaries is different from that observed be-tween larger basins where density driven currents dominate. Here, the process is primarily con-trolled by wind action and tides. On average 5% of the total water volume of Farstaviken is exchanged with Baggensfjärden on daily basis. The bottom oxygen deficiency in Farstaviken during April to November 1997 is partially related to the topography of the basin and the wind sheltering effect. To investigate this issue as well as the sensitivity of mixing to the changes in topography, additional simulations were performed using a modified bathymetry. The original bathymetry was smoothed using the 2D Gaussian filter. The results showed that both the intensi-ties and penetration depths of eddies were increased in comparison with the original bathymetry. The enhanced circulation can also contribute to increase the content of dissolved oxygen near the bottom of Farstaviken.

  • 32.
    Mekonnen, Muluneh Admass
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Gebeyehu, Admasu
    SWECO Environment AB.
    Hydrological modelling of Ethiopian catchments using limited data2009In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 23, no 23, p. 3401-3408Article in journal (Other academic)
    Abstract [en]

    The hydrological component of Soil and Water Assessment Tool (SWAT) model is adapted for Ethiopian catchments based on primary knowledge of the coherence spectrum between dis-charge and runoff. The implication is that only periods longer than about 50 days can be reliably represented in the model based on the available data. An improved method reflecting soil water retention in terms of cumulative evapotranspiration, so that its value is less dependent on soil storage and more dependent on antecedent climate, is used. The improved method is attractive for Ethiopian conditions due to limited soil data availability and the fact that the time-scale of cumulative evaporation can be evaluated over periods longer than 50 days. The spectrum analysis was done on the available nearby climatic data in three watersheds in Ethiopia to analyze the effects of data limitation on the temporal and spatial scales suitable to account for in comparta-mentalized runoff models. The time scales of SWAT for the surface runoff and groundwater flow response were constrained so as to be consistent with the results of the spectrum analysis. The performance of the SWAT model to predict daily stream flow response was compared to the Seasonal Model (SM) and the Original Linear Purturbation Model (OLPM) both of which need previous seasonal behavior of the stream flow.

  • 33.
    Navarro Lérida, Alfonso
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Construction of a dam over the Escartana gully close to Albacete, Spain.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The main aim of this Master Thesis is the design of several hydraulic structures to decrease as much as possible the huge flooding caused by the Escartana gully which drains its water towards the city of Albacete (Spain) and its surrounding areas, affecting to their inhabitants; and causing huge material damages in residential and industrial areas, and loss of crops in nearby farmland.

    Some alternatives such as embankment dams with or without drainage systems inside the dam body and a roller-compacted concrete (RCC) dam have been proposed to be built, being necessary to carry out a multicriteria analysis in order to decide which alternative has the best fit according to the analyzed features of the region. The alternative chosen to be developed was the RCC dam for the advantages of this typology, currently in development and implantation in some countries like Spain.

    For this reason, a RCC dam is planned to be built some kilometers upstream of these areas, with the objective of controlling the future floods coming from this watershed by decreasing its peak flow. In order to increase the beneficial effects of the construction of the dam, a channel downstream is also designed to drain the discharged overflows by the drainage systems of the dam towards a natural endorheic area, the Salobral Lagoon (currently dried-up), located 13 kilometers downstream of the dam’s location. This lagoon is connected hydraulically to the drainage network of Albacete by means of the Salobral channel and due to its huge storage capacity, it allows to reduce substantially the peak flows over the Salobral channel avoiding the dangerous flooding and potential damages caused by them.

    As a result of the projected hydraulic structures, Albacete and its surrounding areas would increase substantially their protection against the floods coming from the Escartana watershed.

  • 34.
    Palm, Per-Martin
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Hydrological investigation for climate change adaptations in the Kou Basin Burkina Faso. : A Minor Field Study.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    One of the biggest upcoming challenges to the international community is the problem of a changing climate. The earth’s surface temperature is rising and associated impacts on physical and biological systems are increasingly being observed. Science tells us that climate change will bring about gradual changes, such as sea level rise, and shifts of climate zones due to increased temperatures and changes in precipitation patterns.

    A changing climate affects the entire world but will strike hardest against the poorest as they are the ones most dependent on agriculture which is a sector that is very vulnerable to changes in temperature and precipitation patterns. One region that will be especially vulnerable and has experienced the problems of shifting climate zones before is the Sahel region that borders to the south end of the Sahara desert where problems of desertification have occurred before. This region will in large extent be affected if the Intergovernmental Panel on Climate Change’s (IPCC) predictions of a rising temperature will become a reality. This is one of the reasons why I have chosen Burkina Faso, situated in the south end of the Sahel region, as the objective for my MFS. The question of rising temperatures will be especially important here as the region is very sensitive to differences in temperature. A crucial topic in this part of the world as well as the topic of this study is the process of adapting to the new climatic situation.

  • 35. Pell, Mikael
    et al.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Biological wastewater treatment systems2008In: Encyclopedia of ecology / [ed] Sven Erik Jorgensen; Brian D Fath, Amsterdam: Elsevier, 2008, p. 426-441Chapter in book (Refereed)
  • 36. Pell, Mikael
    et al.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Biological wastewater treatment systems2009In: Ecosystem Ecology / [ed] Jörgensen, S. E., Academia Press, 2009, p. 166-180Chapter in book (Refereed)
  • 37.
    Pettersson, Kristoffer
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Design of aerators for prevention of cavitation – The Höljes Dam.2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Major cavitation damages can seriously endanger the stability of hydraulic structures, in worst case lead to dam failure. To remedy the effect of cavitation on spillway chutes the most common method today is aeration of the flow.

    Aerators introduce air to the bottom layers of the flow, enough to prevent damages to occur in the concrete lining. The design of an aerator system is of a complex manner due to the many involving parameters such as the channel slope, ramp angle, Froude number, flow velocity.

    In this report the susceptibility of the Höljes Dam to cavitate has been outlined with the result that this would occur at an extreme and most unlikely situation and remedial measures have been proposed. The design of an aerator system has been proposed as the result from theoretical research.

    A physical hydraulic model to assess the efficiency of a proposed aerator design is

    highly recommended.

    Alternative causes to the damages observed in the spillway chute are discussed.

  • 38.
    Riml, Joakim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Hydraulic Engineering (moved 20130630).
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Hydraulic Engineering (moved 20130630).
    Response functions for in-stream solute transport in river networks2011In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 47, no W06502Article in journal (Refereed)
    Abstract [en]

    This paper analyzes the effects of different hydrological mechanisms on the solute response in watershed stream networks. Important processes are due to the hydraulic and chemical retention of reactive solutes in transient storage zones and the cumulative consequences of these processes from a single transport pathway as well as from the network of transport pathways. Temporal moments are derived for a distributed stream network and for a compartment-in-series model. The temporal moments are evaluated and are utilized to derive formal expressions for translating the network parameters into compartmental model parameters. The analysis reveals that in addition to the hydraulic and chemical retention processes, the morphological and topological properties of a watershed have a distinct impact on the central temporal moments in terms of averaging of the solute load weighted distances as well as the transport parameters over the network. Kinetic (rate-limited) transient storage affects second-order and higher central temporal moments and thus has a secondary effect on the parameterization of compartmental models. Additional considerable contributions to all temporal moments are introduced when parameter variability along transport pathways is considered. The paper demonstrates an improved model outcome for phosphorus transport in a small Swedish watershed by accounting for the overall network effects when parameterizing a compartment-in-series model.

  • 39.
    Riml, Joakim
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Hydraulic Engineering.
    Kunkel, Uwe
    Univeristy of Bayreuth.
    Radke, Michael
    Stockholm University.
    Evaluating the fate of six common pharmaceuticals using a reactive transport model: Insights from a stream tracer test2013In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 458, p. 344-354Article in journal (Refereed)
    Abstract [en]

    Quantitative information regarding the capacity of rivers to self-purify pharmaceutical residues is limited. To bridge this knowledge gap, we present a methodology for quantifying the governing processes affecting the fate of pharmaceuticals in streaming waters and, especially, to evaluate their relative significance for tracer observations. A tracer test in Sava Brook, Sweden was evaluated using a coupled physical-biogeochemical model framework containing surface water transport together with a representation of transient storage in slow/immobile zones of the stream, which are presumably important for the retention and attenuation of pharmaceuticals. To assess the key processes affecting the environmental fate of the compounds, we linked the uncertainty estimates of the reaction rate coefficients to the relative influence of transformation and sorption that occurred in different stream environments. The hydrological and biogeochemical contributions to the fate of the pharmaceuticals were decoupled, and the results indicate a moderate hydrological retention in the hyporheic zone as well as in the densely vegetated parts of the stream. Biogeochemical reactions in these transient storage zones further affected the fate of the pharmaceuticals, and we found that sorption was the key process for bezafibrate, metoprolol, and naproxen, while primary transformation was the most important process for clofibric acid and ibuprofen. Conversely, diclofenac was not affected by sorption or transformation.

  • 40.
    Rönnqvist, Hans
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Assessing potential for internal erosion in glacial moraine core embankment dams2007In: Dam Engineering, ISSN 0958-9341, Vol. 18, no 2, p. 101-117Article in journal (Refereed)
    Abstract [en]

    Internal erosion, the process of washout of fine-grained material by seepage flow from an embankment dam filling material, can pose a major threat to dam safety. Internal erosion at a far reached stage can surface in the shape of sinkholes, sudden turbid leakages and settlements, indicating that the filling material in the dam is undergoing potentially significant property changes. It was early on found, for instance by Sherard [1979], that embankment dams comprising broadly graded material appear to develop sinkholes more frequent than dams of other material components. And considering that typical Swedish embankment dams are composed of material with broad and wide gradations of glacial origin, in particular the impervious core of broadly graded moraine (till), it should come as no surprise that many embankment dams in Sweden have shown signs of deterioration that can be related to internal erosion. The susceptibility for internal erosion in Swedish embankment dams was perhaps first noticed in a survey carried out by Nilsson et al [1999], where 20 % of the incorporated dams were estimated being affected by internal erosion. To reduce the risks connected to internal erosion it can be necessary to implement dam safety measures preferably at an early stage before the internal erosion progressed to surfacing, but distinguishing which dams that hold a real potential future risk for internal erosion can prove difficult. This paper is based on an evaluation comprising 45 existing Swedish embankment dams and the results show that a more discriminatory predictor, than today’s filter criteria, appears to be needed if embankment dams with widely graded glacial cores with high potential for surfacing internal erosion are to be singled out from dams apparently internal erosion free. The results indicate that not only filter coarseness needs to be addressed when assessing potential for internal erosion in embankment dams with glacial moraine cores, but also the internal stability of the core and filter.

  • 41.
    Rönnqvist, Hans
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Long-term behaviour of internal erosion afflicted dams comprising broadly graded soils2009In: Dam Engineering, ISSN 0958-9341, Vol. 20, no 2, p. 149-197Article in journal (Refereed)
    Abstract [en]

    Internal erosion occurs when fine-grained particles are washed out from a filling material by seepage. Sinkholes and settlements on the dam crest, sudden increased leakage, or muddy seepage may be manifestations of progressed internal erosion. Dams with cores of glacially formed broadly graded soils have been found to be more likely to experience internal erosion than dams composed of other materials. This paper describes and reviews case histories of 30 existing dams constructed from broadly graded soils with performance history of internal erosion. Understanding i) typical signs and observations of internal erosion, ii) the timing of internal erosion incidents, iii) the possible early-warning signs, iv) the possible warning-time, and v) the location of the internal erosion incident on the dam body – may provide tools for early-warning detection of internal erosion prone dams and improve the assessment of internal erosion in existing dams.

  • 42.
    Rönnqvist, Hans
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Predicting surfacing internal erosion in moraine core dams2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Dams that comprise broadly and widely graded glacial materials, such as moraines, have been found to be susceptible to internal erosion, perhaps more than dams of other soil types. Internal erosion washes out fine-grained particles from the filling material; the erosion occurs within the material itself or at an interface to another dam zone, depending on the mode of initiation. Whether or not internal erosion proceeds depend on the adequacy of the filter material. If internal erosion is allowed, it may manifest itself as sinkholes on the crest, increased leakage and muddy seepage once it surfaces, which here is called surfacing internal erosion (i.e. internal erosion in the excessive erosion or continuation phase). In spite of significant developments since the 1980s in the field of internal erosion assessment, the validity of methods developed by others on broadly graded materials are still less clear because most available criteria are based on tests of narrowly graded granular soils. This thesis specifically addresses dams that are composed of broadly graded glacial soils and investigates typical indicators, signs and behaviors of internal erosion prone dams. Based on a review of 90+ existing moraine core dams, which are located mainly in Scandinavia as well as North America and Australia/New Zealand, this thesis will show that not only the filter’s coarseness needs to be reviewed when assessing the potential for internal erosion to surface (i.e., erosion in the excessive or continuing phase); in addition, the grading stability of the filter and the core material as well as non-homogeneities that are caused by filter segregation need to be studied. Cross-referencing between these aspects improves the assessment of potential for internal erosion in dams of broadly graded soils and furthermore it provides aid-to-judgment.

  • 43.
    Rönnqvist, Hans
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Review of moraine core dams and internal erosion2008In: Dam Engineering, ISSN 0958-9341, Vol. 19, no 2, p. 99-121Article in journal (Refereed)
    Abstract [en]

    Embankment dams comprising broadly graded materials of glacial origin have in the past been identified as being prone to develop sinkholes more frequent than dams composed of materials of other origin. Sinkholes on the crest of a dam are many times an indicator of internal erosion. Internal erosion can initiate and continue to develop for many reasons, but mainly due to root causes coming from core/filter properties and interaction, possibly affected by the dam design and/or construction related reasons. In this paper a review is made on moraine core dams in the literature in relation to performance history of internal erosion. Dam data comprising 90 existing moraine core embankment dams has been compiled and assessed with objective to investigate the occurrence of indicative properties of dams that have developed internal erosion. The data set of dams consists predominately of Swedish dams, but it also includes moraine core dams located in the rest of Scandinavia, in North America, Russia and Australia. The investigation shows that a coarsely graded filter, grading instability of the core and filter, and high susceptibility for filter segregation are properties that are over-represented and possibly indicative for moraine (till) core dams with performance history of internal erosion.

  • 44.
    Rönnqvist, Hans F.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Hydraulic Engineering (moved 20130630).
    Long-term behaviour of dams with internal erosion2009In: International Water Power and Dam Construction, ISSN 0306-400X, Vol. 61, no 7, p. 34-36Article in journal (Refereed)
    Abstract [en]

    The performance history and long-term behavior of the dams mainly comprises of the internal erosion process of graded glacial soil associated with washout of fine grained particles from a dam's filling material by seepage. Internal erosion initiates generally by concentrated leak erosion, backward erosion, and/or suffusion. 30 existing dams comprising broadly graded soils of glacial origin that is, moraines and tills have been reviewed. These are all dams that have differing extents, and have experienced incidents of internal erosion. Incidents are most likely to occur early-on, since almost half of the dams reviewed experienced incidents during first filling or within the first year of service. The most common signs that precede an internal erosion related incident are increase in leakage, muddy leakage and pore-pressure variations in the dam body.

  • 45. Setegn, S.G.
    et al.
    Rayner, D.
    Melesse, A.M.
    Dargahi, B.
    Srinivasan, R.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Climate Change impact on Agricultural Water Resources Variability in the Northern Highlands of Ethiopia2011In: Nile River Basin: Hydrology, Climate and Water Use / [ed] Melesse, Assefa M., Springer-Verlag New York, 2011, 1st, p. 241-265Chapter in book (Refereed)
  • 46.
    Setegn, Shimelis Gebriye
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Calibration and validation of SWAT2005/ArcSWAT in Anjeni gauged watershed, northern highlands of Ethiopia2007In: Proceedings of the 4th International SWAT Conference, 2007, p. 375-384Conference paper (Other academic)
  • 47.
    Setegn, Shimelis Gebriye
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Hydrological and sediment yield modelling in Lake Tana Basin, Blue Nile Ethiopia2008Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Land and water resources degradation are the major problems on the Ethiopian highlands. Poor land use practices and improper management systems have played a significant role in causing high soil erosion rates, sediment transport and loss of agricultural nutrients. So far limited meas-ures have been taken to combat the problems. In this study a physically based watershed model, SWAT2005 was applied to the Northern Highlands of Ethiopia for modelling of the hydrology and sediment yield. The main objective of this study was to test the performance and feasibility of SWAT2005 model to examine the influence of topography, land use, soil and climatic condi-tion on streamflows, soil erosion and sediment yield. The model was calibrated and validated on four tributaries of Lake Tana as well as Anjeni watershed using SUFI-2, GLUE and ParaSol algo-rithms. SWAT and GIS based decision support system (MCE analysis) were also used to identify the most erosion prone areas in the Lake Tana Basin. Streamflows are more sensitive to the hy-drological response unites definition thresholds than subbasin discretization. Prediction of sedi-ment yield is highly sensitive to subbasin size and slope discretization. Baseflow is an important component of the total discharge within the study area that contributes more than the surface runoff. There is a good agreement between the measured and simulated flows and sediment yields with higher values of coefficients of determination and Nash Sutcliffe efficiency. The an-nual average measured sediment yield in Anjeni watershed was 24.6 tonnes/ha. The annual aver-age simulated sediment yield was 27.8 and 29.5 tonnes/ha for calibration and validation periods, respectively. The SWAT model indicated that 18.5 % of the Lake Tana Basin is erosion potential areas. Whereas the MCE result indicated that 25.5 % of the basin are erosion potential areas. The calibrated model can be used for further analysis of the effect of climate and land use change as well as other different management scenarios on streamflows and soil erosion. The result of the study could help different stakeholders to plan and implement appropriate soil and water conser-vation strategies.

  • 48.
    Setegn, Shimelis Gebriye
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Modelling Hydrological and Hydrodynamic Processes in Lake Tana Basin, Ethiopia2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Lake Tana Basin is of significant importance to Ethiopia concerning water resources aspects and the ecological balance of the area. The growing high demands in utilizing the high potentials of water resource of the Lake to its maximal limit, pictures a disturbing future for the Lake. The objective of this study was to assess the influence of topography, soil, land use and climatic varia-bility on the hydrological and hydrodynamic processes of the Lake Tana Basin. The physically based SWAT model was successfully calibrated and validated for flow and sediment yield. Se-quential uncertainty fitting (SUFI-2), parameter solution (ParaSol) and generalized likelihood un-certainty estimation (GLUE) calibration and uncertainty analysis methods were compared and used for the set-up of the SWAT model. There is a good agreement between the measured and simulated flows and sediment yields. SWAT and GIS based decision support system that uses multi-criteria evaluation (MCE) was used to identify the most vulnerable areas to soil erosion in the basin. The results indicated that 12 to 30.5% of the watershed is high erosion potential. Pro-jected changes in precipitation and temperature in the basin for two seasons were analyzed using outputs from fifteen global climate models (GCMs). A historical-modification procedure was used to downscale large scale outputs from GCM models to watershed-scale climate data. The results showed significant changes in streamflow and other hydrological parameters in the period between 2045-2100. SWAT was combined with a three dimensional hydrodynamic model, GEMSS to investigate the flow structure, stratification, the flushing time, lake water balance and finally the Lake‘s water level response to planned water removal. We have found an alarming and dramatic fall of the water levels in Lake Tana as response to the planned water withdrawal. The combination of the two models can be used as a decision support tools to better understand and manage land and water resources in watersheds and waterbodies. The study showed that the Lake Tana Basin may experience a negative change in water balance in the forthcoming decades due to climate change as well as over abstraction of water resources.

  • 49.
    Setegn, Shimelis Gebriye
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Srinivasan, Ragahavan
    Texas A & M University, Spatial Science Laboratory.
    Sediment Yield Modelling from Anjeni Gauged Watershed, Ethiopia using SWAT2005 Model2008In: The Open Hydrology Journal, ISSN 1874-3781Article in journal (Other academic)
  • 50.
    Setegn, Shimelis Gebriye
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Dargahi, Bijan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Hydraulic Engineering.
    Srinivasan, Ragahavan
    Melesse, Assefa M.
    Modeling of Sediment Yield From Anjeni-Gauged Watershed, Ethiopia Using SWAT Model2010In: Journal of the American Water Resources Association, ISSN 1093-474X, E-ISSN 1752-1688, Vol. 46, no 3, p. 514-526Article in journal (Refereed)
    Abstract [en]

    The Soil and Water Assessment Tool (SWAT) was tested for prediction of sediment yield in Anjeni-gauged watershed, Ethiopia. Soil erosion and land degradation is a major problem on the Ethiopian highlands. The objectives of this study were to evaluate the performance and applicability of SWAT model in predicting monthly sediment yield and assess the impacts of subbasin delineation and slope discretization on the prediction of sediment yield. Ten years monthly meteorological, flow and sediment data were used for model calibration and validation. The annual average measured sediment yield was 24.6 tonnes/ha. The annual average simulated sediment yield was 27.8 and 29.5 tones/ha for calibration and validation periods, respectively. The study found that the observed values showed good agreement with the simulated sediment yield with Nash-Sutcliffe efficiency (NSE) = 0.81, percent bias (PBIAS) = 28%, RMSE-observations standard deviation ratio (RSR) = 0.23, and coefficient of determination (R superset of) = 0.86 for calibration and NSE = 0.79, PBIAS = 30%, RSR = 0.29, and R superset of = 0.84 for validation periods. The model can be used for further analysis of different management scenarios that could help different stakeholders to plan and implement appropriate soil and water conservation strategies.

12 1 - 50 of 88
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf