Dr. Diplas, together with his research group, study phenomena related to the dynamics of water, sediment and contaminant transport through waterways, floodplains and wetlands. Our work is focused on the interaction of the aforementioned components with infrastructure, vegetation and biota. Relevant research areas include: environmental, fluvial, ecological and infrastructure hydraulics; sustainable development and hydrokinetic energy generation.

Our research philosophy and methodology are summarized by the following statements:

  • Develop theoretical understanding of empirical reality
  • Solve real engineering problems by examining the phenomena from a fundamental point of view
  • Use state-of-the-art experimental facilities, computational, field and analytical techniques to develop better understanding of cause and effect relations

Our group has pursued innovative research on the role of fluctuating turbulent forces on particle movement and other hydraulic phenomena, scour around bridge piers and abutments, design of in-stream structures, river mechanics and morphology, stream restoration, ecological hydraulics, wetland hydrodynamics and renewable energy. Federal and state agencies that have supported our research efforts include the National Science Foundation; U.S. Army Corps of Engineers; Environmental Protection Agency; Federal Highway Administration; U.S. Geological Survey; NASA; Department of Energy; Defense Advanced Research Projects Agency; Virginia Department of Transportation and the Virginia Department of Game and Inland Fisheries. Representative sponsors from industry and nonprofit organizations include Pacific Gas & Electric, Dominion Power, and The Nature Conservancy.

Dr. Diplas has authored more than 200 refereed publications and given numerous invited lectures, keynote addresses and presentations.  A former NSF National Young Investigator Award recipient, in 2021 Diplas received the Hunter Rouse Hydraulic Engineering Award from ASCE for fundamental contributions to the role of turbulence in sediment transport, ecohydraulics, stream restoration and scour.  Additionally, in 2012 he was recognized by ASCE with the H.A. Einstein Award for his significant contributions to the understanding of river mechanics, erosional processes and sediment transport. In 2010 ASCE awarded him the Karl Emil Hilgard Prize for the year’s best hydraulics paper, which was published in the Journal of Hydraulic Engineering.  He was elected a Fellow of EWRI (Environmental and Water Resources Institute) in 2015 and a Fellow of ASCE in 2018.  During the spring semester of 2007 Diplas was the Braun Intertec Visiting Professor in the department of civil engineering at the University of Minnesota. Before joining Lehigh in 2013, where he served as department chair from 2013 to 2020, Diplas was on the faculty of Virginia Tech for 25 years. In 1999 he founded the Baker Environmental Hydraulics Laboratory and served as its director for 14 years.



Teaching and Service

Dr. Diplas teaches courses in Fluid Mechanics, Open Channel Flow, Watershed Management, and River Mechanics. In 1993 he received a Certificate of Teaching Excellence from Virginia Tech. He has guided 50 M.S. and Ph.D. theses to completion.  Nine of his Ph.D. students currently serve in academia as faculty members, while others play a leading role in various government agencies and the industry.  He has also supervised 15 postdoctoral researchers and visiting faculty. Has served on the editorial board of many journals and co-organized two international conferences.


Selected Publications

Heydari, N., and Diplas, P., “Flow dynamics in the vicinity of a gravel embedded vertical retaining wall: Conditions corresponding to the initial stages of local erosion.” Accepted and available on line Journal of Environmental Fluid Mechanics, doi.org/10.1007/s10652-019-09715-8, 2019.

Khosronejad, A., Diplas, P., Angelidis, D., Zhang, Z., Heydari, N., and Sotiropoulos, F., “Scour depth prediction at the base of longitudinal walls: A combined experimental, numerical, and field study.” Accepted and available on line Journal of Environmental Fluid Mechanics, doi.org/10.1007/s10652-019-09704-x, 2019.
Shih, W. and Diplas, P., “Threshold of motion conditions under Stokes flow regime and comparison with turbulent flow data.” Water Resources Research, AGU, doi.org/10.1029/2019WR024836, 55(12):10872-10892, 2019.
Ban, X., Diplas, P., Shih, W-R, Xiao, F., and Shi, X-T “Impact of Three Gorges Dam operation on the spawning success of four major Chinese carps.” Ecological Engineering, doi.org/10.1016/j.ecoleng.2018.12.004, 127: 268-275, February 2019.
Shih, W. and Diplas, P., "A unified approach to bedload transport description over a wide range of flow conditions via the use of conditional data treatment." Water Resources Research, AGU, doi.org/10.1029/2017WR022373, 54: 3490-3509, June 2018.

Jha, R. and Diplas, P., "Elevation, a consistent and physically-based framework for classifying stream channels." Journal of Hydraulic Research, doi.org/10.1080/00221686.2017.1354928, IAHR, 58(3): 299-312, June 2018.

Khosronejad, A., Kozarek, L. J., Diplas, P., Hill, C., Jha, R., Chatanantavet, P., Heydari, N., and Sotiropoulos, F., "Simulation-based optimization of in–stream structures design: Rock vanes." Environmental Fluid Mechanics, doi.org/10.1007/s10652-018-9579-7, 18(3): 695-738, June 2018.

Deskos, G. and Diplas, P., "Incipient motion of a non-cohesive particle under Stokes flow conditions." International Journal of Multiphase Flow, doi.org/10.1016/j.ijmultiphaseflow.2017.09.015, 99: 151-161, February 2018.

Shih, W., Diplas, P., Celik, A.O., and Dancey, C., "Accounting for the role of turbulent flow on particle dislodgement via a coupled quadrant analysis of velocity and pressure sequences." Advances in Water Resources, doi.org/10.1016/j.advwatres.2017.01.005, 101: 37-48, March 2017.

Khosronejad, A., Diplas, P., and Sotiropoulos, F., "Simulation-based optimization of in-stream structures design: Bendway weirs." Environmental Fluid Mechanics, doi.org/10.1007/s10652-016-9452-5, 17(1): 79–109, February 2017.

Bouratsis, P., Diplas, P., Dancey, C.L., and Apsilidis, N., "Quantitative spatio-temporal characterization of scour at the base of a cylinder." Water, doi.org/10.3390/w9030227, 9(227): 1-17, March 2017.

Petrie, J. and Diplas, P., "Evaluation of the logarithmic law of the wall for river flows." River Research and Applications, doi.org/10.1002/rra.2920, 32(5):1082-1093, June 2016.

Apsilidis, N., Diplas, P., Dancey, C., and Bouratsis, P., "Effects of Wall Roughness on Turbulent Junction Flow Characteristics." Experiments in Fluids, doi.org/10.1007/s00348-015-2098-0, 57(issue 1; article 12): 1-16, January 2016.

Khosronejad, A., Kozarek, J., Diplas, P., and Sotiropoulos, F., "Simulation-based approach for stream restoration structure design: J-hook vane structures." Journal of Hydraulic Research, IAHR, doi.org/10.1080/00221686.2015.1093037, 53(5): 588-608, 2015.

Apsilidis, N., Diplas, P., Dancey, C.L., and Bouratsis, P., “Time-resolved flow dynamics and Reynolds number effects at a wall-cylinder junction.” Journal of Fluid Mechanics, doi.org/10.1017/jfm.2015.341, 776: 475–511, August 2015.

Weiss, R. and Diplas, P., “Untangling boulder dislodgement in storms and tsunamis: Is it possible with simple theories?” Journal of Geochemistry, Geophysics, Geosystems (G-Cubed), AGU, doi.org/10.1002/2014GC005682, 16(3): 890–898, March 2015.

Celik, A.O., Diplas, P. and Dancey, C.L., “Instantaneous Pressure Measurements on a Spherical Grain under Threshold Flow Conditions.” Journal of Fluid Mechanics, doi:10.1017/jfm.2013.632, 741: 60-97, 2014.

Diplas, P. and Dancey, C.L., “Particle movement subject to a fluctuating fluid force.” McGraw-Hill Yearbook of Science and Technology, pp. 274-277, 2014.

Bolinaga, C.F.C. and Diplas, P., “Hydraulic Modeling of Extreme Hydrologic Events: Case Study in Southern Virginia.” Journal of Hydraulic Engineering, ASCE, 140(12): 1-12, 2014.

Petrie, J., Diplas, P., Gutierrez, M. and Nam, S., “Characterizing the Mean Flow Field in Rivers for Resource and Environmental Impact Assessments of Hydrokinetic Energy Generation Sites.” Renewable Energy, doi.org/10.1016/j.renene.2014.03.064, 69: 393-401, September 2014.

Petrie, J., Diplas, P., Gutierrez, and Nam, S., “Combining Fixed- and Moving-vessel Acoustic Doppler Current Profiler Measurements for Improved Characterization of the Mean Flow in a Natural River.” Water Resources Research, AGU, 49: 5600-5614, doi:10.1002/wrcr.20396, 2013.

Plott, J.R., Diplas, P., Kozarek, J., Dancey, C.L., Hill, C., and Sotiropoulos, F., “A Generalized Log Law Formulation for a Wide Range of Boundary Roughness Typically Encountered in Natural Streams.” Journal of Geophysical Research: Earth Surface, AGU, 118: 1419-1431, doi:10.1002/jgrf.20104, 2013.

Celik, A.O., Diplas, P., and Dancey, C.L., “Instantaneous Turbulent Forces and Impulse on a Rough Bed: Implications for Initiation of Bed Material Movement.” Water Resources Research, AGU, 49(4): 2213–2227, doi:10.1002/wrcr.20210, 2013.

Bouratsis, P., Diplas, P., Dancey, C.L., and Apsilidis, N., “High-resolution 3D Monitoring of Evolving Sediment Beds.” Water Resources Research, AGU, 49(2): 977-992, doi:10.1002/wrcr.20110, 2013.

Valyrakis, M., P. Diplas, and C.L. Dancey, “Entrainment of Coarse Particles in Turbulent Flows: An Energy Approach.” Journal of Geophysical Research: Earth Surface, AGU, 118: 42–53, doi:10.1029/2012JF002354, March  2013.

Petrie, J., Diplas, P., M. Gutierrez, and Nam, S., “Data Evaluation for Acoustic Doppler Current Profiler Measurements Obtained at Fixed Locations in a Natural River.” Water Resources Research, AGU, 49(2): 1003-1016, doi:10.1002/wrcr.20112, 2013.

Diplas, P. and Dancey, C.L., “Coherent Flow Structures, Initiation of Motion, Sediment Transport and Morphological Feedbacks in Rivers.” Chapter 19 in ‘Coherent Flow Structures in Geophysical Flows at the Earth’s Surface,’ Edited by J.G. Venditti, J. Best, M. Church, R.J. Hardy, John Wiley & Sons, pp. 289-307, 2013.

Sotiropoulos, F., Diplas, P., and Khosronejad, A., “Scour Around Bridge Foundations.” Handbook of Environmental Fluid Dynamics, Edited by H.J.S. Fernando, Taylor & Francis, Vol. 2, pp. 69-84, 2012.

Neary, V., Constantinescu, G., Bennett, S., and Diplas, P., “Effects of Vegetation on Turbulence, Sediment Transportation and Stream Morphology.” Journal of Hydraulic Engineering, ASCE, 138(9): 765-776, 2012.

Valyrakis, M., Diplas, P., and Dancey, C.L., “Prediction of Coarse Particle Movement with Adaptive Neuro-fuzzy Inference Systems.” Hydrological Processes, 25: 3513-3524, doi:10.1002/hyp.8228, Oct. 2011.

Nam, S., Gutierrez, M., Diplas, P., and Petrie, J., “Determination of the Shear Strength of Unsaturated Soils Using the Multistage Direct Shear Test.” Journal of Engineering Geology, 122: 272-280, Oct. 2011.

Valyrakis, M., Diplas, P., and Dancey, C.L., “Entrainment of Coarse Grains in Turbulent Flows: an Extreme Value Theory Approach.” Water Resources Research, AGU, 47(9): 1-17, doi:10.1029/2010WR010236, 2011.

Liu, D., Diplas, P., Hodges, C.C., and Fairbanks, J.D., “Hydrodynamics of Flow through Double Layer Rigid Vegetation.” Journal of Geomorphology, 116(3-4): 286-296, 2010.

Dietz, C.M., Diplas, P., and Horsch, G., “A Spectral Method Determination of the First Critical Rayleigh Number for a Low-Prandtl Number Melt in a Cylindrical Container.” Journal of Applied Mathematical Modeling, 34(8): 2178-2191, 2010.

Nam, S., Gutierrez, M., Diplas, P., Petrie, J., Wayllace, A., Lu, N., and Munoz, J.J., “Comparison of Testing Techniques and Models for Establishing the SWCC of Riverbank Soils.” Journal of Engineering Geology, 110(1-2): 1-10, 2010.

Celik, A.O., Diplas, P., Dancey, C.L., and Valyrakis, M., “Impulse and particle dislodgement under turbulent flow conditions.” Physics of Fluids, doi:10.1063/1.3385433, 046601, 22: 1-13, April 2010. 

Diplas, P., Celik, A.O., Dancey, C.L., and Valyrakis, M., “Non-intrusive Method for Detecting Particle Movement Characteristics near Threshold Flow Conditions.” Journal of Irrigation and Drainage, ASCE, 136(11): 774-780, 2010.

Radspinner, R., Diplas, P., Lightbody, A., and Sotiropoulos, F., “River Training and Ecological Enhancement Potential Using In-Stream Structures.” Journal of Hydraulic Engineering, ASCE, 136(12): 967-980, 2010.

Shen, Y. and Diplas, P., “Modeling Unsteady Flow Characteristics of Hydropeaking Operations and their Implications on Fish Habitat.” Journal of Hydraulic Engineering, ASCE, 136(12): 1053-1066, 2010.

Stoesser, T., Kim, S.J, and Diplas, P., “Turbulent Flow through Idealized Emergent Vegetation.” Journal of Hydraulic Engineering, ASCE, 136(12): 1003-1017, 2010.

Valyrakis, M., Diplas, P., Dancey, C.L., Greer, K., and Celik, A.O., “The role of instantaneous force magnitude and duration on particle entrainment.” Journal of Geophysical Research-Earth Surface, AGU, 115: 1-18, doi:10.1029/2008JF001247, April, 2010.

Stoesser, T., Salvador, G.L, Rodi, W., and Diplas, P., “Large Eddy Simulation of Turbulent Flow through Submerged Vegetation.” Transport in Porous Media, 78: 347-365, doi:10.1007/s11242-009-9371-8, July 2009.

Diplas, P., Dancey, C.L., Celik, A.O., Valyrakis, M., Greer, K., and Akar, T., “The role of impulse on the initiation of particle movement under turbulent flow conditions". Science, 322: 717-720, doi:10.1126/science.1158954, October 31, 2008.

Liu, D., Diplas, P., Fairbanks, J.D. and Hodges, C.C., “An experimental study of flow through rigid vegetation.” Journal of Geophysical Research-Earth Surface, AGU, 113:1-16, doi:10.1029/2008JF001042, December 19, 2008.

Shen, Y. and Diplas, P., “Application of Two- and Three-dimensional Computational Fluid Dynamics Models to Complex Ecological Stream System Flows.” Journal of Hydrology, 348(1-2): 195-214, doi:10.1016/j.jhydrol.2007.09.060 2008.

Panayiotis Diplas
P.C. Rossin Professor, Water Resources Engineering
(610) 758-3554
1 West Packer Avenue
9A - STEPS Bldg.
Bethlehem, PA 18015-3176


Ph.D., Civil Engineering, University of Minnesota
M.S., Civil Engineering, University of Minnesota
B.S., Civil Engineering, National Technical University of Athens, Greece