Achilleas G. Tsakiris

  • Graduate Research Assistant
  • IIHR—Hydroscience & Engineering
  • Department of Civil & Engineering
  • 100 C. Maxwell Stanley Hydraulics Lab
    Iowa City, IA 52242
    Office: 323-XX SHL
    Phone: 319-335-6448
    Fax: 319-335-5238
    1-MainAchillesPicture I am currently pursuing my Ph.D. in the Hydraulics and Water Resources Program at the IIHR-Hydroscience and Engineering, after having completed my M.Sc. in the same program. I am originally from Greece and my hometown, Xanthi, is located in the north-east of the country. I have recently been recently engaged to my fiancé, Viviane, who has always stood by me. My research project focuses on the effects that large boulders, which are often found in mountainous stream reaches have on the patterns of sediment particle transport dynamics through their interaction with the approaching turbulent flow field. This project consists of laboratory experiments designed to looking into relating the turbulent flow field characteristics in the vicinity of the boulders with mechanistically relate this flow field to sediment transport dynamics. Ultimately, this work aims to develop a modern sediment transport relation accounting for the effects of boulder arrays, which would provide practicing engineers working on mountain stream restoration and monitoring projects a useful tool for predicting bedload transport rates.

    Research Direction

    - Sediment and Flow Dynamics within Boulder Arrays
    I am looking into the characteristics of the mean turbulent flow field which develops around a boulder. We are using state-of-the-art measuring equipment, such as Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV) to determine instantaneous and time averaged parameters describing the flow field around the boulder such as velocity, vorticity and bed shear stress. While my work is more related to the time-averaged description of the flow field, my project mate Seyed Hajimirzaie (Haji) is investigating the instantaneous nature of the turbulent velocity field developing around a boulder.


    Boulder Array


    Dye Injection into flume

    In parallel, we investigate the bedload rates and the dynamics of bedload particle motion throughout the boulder array. To achieve this we are using video analysis techniques but also a suite of other instruments such as passive acoustic sensors (geophones), which determine bedload transport rates from the acoustic signature of bedload particles impacting the sensor, and Radio Frequency ID (RFID) particle tracers for a Lagrangian description of bedload dynamics.

    Sediment Movement


    RFID tracers


    Geophone plates in the flume bed


    InfraRed Technology

    Throughout, my tenure in the IIHR-Hydroscience and Engineering, I have been exposed to a variety of research projects, which have contributed to my critical thinking ability. For example I was involved in the fluidization project, where we the studied formation of channels in fluidized mud layers. Using modern instrumentation, including a gamma radiation source and pressure transducers, we quantified the conditions, which lead to the formation of these vents.

    Fluidization experimental setup

    Fluidization Volcano Close-Up

    Fluidization Volcano Close-Up

    -Cluster Morphologic Characterization
    The research project of my M.Sc. also related to processes in gravel streams and more specifically to clusters, which are a small-scale bedform in mountain streams arising from the organization of the surface sediment into patches. It involved the characterization of different cluster morphologies, which our group had previously identified in field and laboratory work. To this end, we applied fractal analysis on images of clusters taken in the field and in the laboratory and quantitatively discerned cluster morphology into two families, namely the in-line and the non-linear cluster morphologies. We have hypothesized that these cluster morphology families are outcome of different flow and sediment supply conditions in mountain streams.


    Box Counting Animation


    Box Counting

    Selected Publications

    1. Papanicolaou, A.N., Kramer, C.M., Tsakiris, A.G., Stoesser, T., Bomminayuni, S. and Chen, Z. (2012) Effects of a Fully Submerged Boulder Within a Boulder Array on the Mean and Turbulent Flow Fields: Implications to Bedload Transport, Acta Geophysica, Springerlink DOI: 10.2478/s11600-012-0044-6.
    2. Papanicolaou, A.N., Tsakiris, A.G. and Strom, K.B. (2011) The use of fractals to quantify the morphology of cluster microforms, Geomorphology (Elsevier), Vol. 139-140, p. 91-108.
    3. Tsakiris, A.G. and Papanicolaou, A.N. (2008) A Fractal Approach For Characterizing Microroughness in Gravel Bed Streams, Archives of Hydro-Engineering & Environmental Mechanics (Polish Academy of Sciences), Vol. 55, No. (1), p. 3-17.

    Selected Posters and Presentations

    1. Tsakiris, A.G., Hajimirzaie, S.M., Papanicolaou, A.N. and Buchholz, J.B. Effects of a Boulder Array Under Low and High Relative Submergence on Roughness: Implication on Bedload Rates, American Geophysical Union (AGU) Fall Meeting, San Francisco, CA USA, December 3-7, 2012.
    2. Papanicolaou, A.N., Tsakiris, A.G., and Billing, B.M. The Onset of Channelling in a Fluidized Mud Layer, American Geophysical Union (AGU) Fall Meeting, San Francisco, CA USA, December 3-7, 2012.
    3. Tsakiris, A.G., Papanicolaou, A.N. Calibration of an Acoustic Sensor (Geophone) for Continuous Bedload Monitoring in Mountainous Streams, American Geophysical Union (AGU) Fall Meeting, San Francisco, CA, December 13-17, 2010.
    4. Tsakiris, A.G. and Papanicolaou, A.N. A Method to Describe Microroughness in Gravel Streams, International Conference on Fluvial Hydraulics, Riverflow 2008, Cesme-Izmir, Turkey, September 3-5, 2008.


    Conference presentation from Athens in 2010


    Honors, Awards, Fellowships and Scholarships

    • Outstanding Reviewer for 2013, Journal of Hydraulic Engineering, ASCE (2014)
    • Civil & Environmental Engineering Dissertation Year Fellowship, The University of Iowa (2013).
    • Paul C. and Sarah Jane Benedict Award for Study of Alluvial River Processes (2012-2013).
    • British Society of Geomorphology for the Presentation “Calibration of an Acoustic Sensor (Geophone) for Continuous Bedload Monitoring in Mountainous Streams”s during the American Geophysical Union (AGU) Fall Meeting 2010, San Francisco, CA (2010).
    • Paul C. and Sarah Jane Benedict Award for Study of Alluvial River Processes (2010).
    • Graduate Research Assistanship, IIHR-Hydroscience and Engineering, The University of Iowa (2005-Present).
    • Travel Award, Graduate Student Senate (GSS), The University of Iowa (2009).
    • Travel Award, Center for Global and Regional Environmental Research (CGRER), The University of Iowa (2007, 2008 and 2009).