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" The Study of Flow Hydrodynamics and Transport Processes over Mixed Bedrock-Alluvial Reaches "
Jafarinik, Mohammad Sadegh
Viparelli, Enrica
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Latin Dissertation
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English
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| Record Number
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1052499
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| Doc. No
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TL51616
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| Main Entry
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Jafarinik, Mohammad Sadegh
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| Title & Author
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The Study of Flow Hydrodynamics and Transport Processes over Mixed Bedrock-Alluvial Reaches\ Jafarinik, Mohammad SadeghViparelli, Enrica
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| College
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University of South Carolina
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| Date
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2019
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| Degree
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Ph.D.
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2019
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| Note
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125 p.
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| Abstract
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Research efforts on mixed bedrock-alluvial rivers primary focused on the bedrock incision and very few studies investigated the alluvial morphodynamics of such systems. To the best of my knowledge none of these models have been considered the spatial variability of the sediment grain size of the bed surface in mixed bedrock-alluvial reaches and very few models focused on the spatial changes in alluvial cover within these reaches. Furthermore, a perusal of the literature on mixed bedrock-alluvial river morphodynamics reveals that very little information is available on the spatial changes associated with bedform geometry and consequently flow resistances associated with the interaction between bedload transport and a non-erodible bedrock surface. Understanding the interactions between the flow and the sediment transport processes in mixed bedrock-alluvial rivers carrying nonuniform material is necessary to predict the long-term river responses to any anthropogenic changes, their impacts on the large scale sediment budget and on the quality of the riparian habitat. I thus designed and performed a set of laboratory experiments to investigate the effects of bedrocks on the flow and sediment transport processes in mixed bedrock-alluvial reaches characterized by a bedrock surface slope that is milder than the alluvial equilibrium slope of the alluvial system subjected to the same flow conditions and sediment supply of the mixed bedrock-alluvial systems. I also derived a novel mathematical formulation to model the alluvial morphodynamics of mixed bedrock-alluvial reaches transporting non-uniform bed material and implemented this formulation in a one-dimensional model of river morphodynamics. The experiments revealed that equilibrium conditions in these mixed bedrock-alluvial systems are characterized by flow acceleration in the streamwise direction. The morphodynamic response to this change of flow hydrodynamics is characterized by 1) a streamwise reduction in the alluvial cover, 2) a reduction in height of the bedforms, and 3) the formation of a pattern of downstream fining of the bed surface sediment. The mathematical formulation for the alluvial morphodynamics of mixed bedrock-alluvial rivers was validated at laboratory scale against the experimental results. The validated model was used to study the changes in flow hydrodynamics and sediment transport processes in mixed bedrock-alluvial reaches characterized by a bedrock surface slope that was steeper than the alluvial equilibrium slope of a channel subjected to the same flow regime and sediment supply of the mixed bedrock-alluvial reach of interest. The numerical results at equilibrium show that in this case the interaction between the flow, the sediment transport and the non-erodible bedrock surface was different from the one with the bedrock surface slope milder than the alluvial equilibrium slope. In this case the flow velocity decreased on the bedrock reach in streamwise direction. The effects of this spatial flow deceleration on the sediment transport processes resulted in 1) a streamwise increase in alluvial cover, and 2) the formation of a pattern of downstream coarsening of the bed surface sediment. Due to the limitation of the model formulation, I was not able to predict the spatial changes in bedform geometry associated with the predicted characteristics of the flow. In the very near future the morphodyanmic formulation presented in this dissertation will be applied at field scale on the gravel bed Buech River, Southeastern France, to study the impacts of anthropogenic activities such as dam construction and gravel mining, and to identify possible restoration strategies to control the observed widespread erosion of the gravel bed and the associated deterioration of the aquatic and riparian habitat.
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Civil engineering
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Geomorphology
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Geophysics
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Hydraulic engineering
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Hydrologic sciences
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Limnology
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Sedimentary geology
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Water resources management
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Viparelli, Enrica
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University of South Carolina
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