Thanos Papanicolaou
IIHR - Hydroscience & Engineering, The University of Iowa

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Application Note: Sediment Transport
 
Cohesive Sediment: Understanding the mechanisms involved in the transport and fate of cohesive sediment in natural channel systems along with effects on aquatic organisms remains an open case in water-related engineering disciplines.  The main challenge is that cohesive sediment dynamics are controlled not only by physical forces (e.g., inertia, buoyancy, drag, lift, friction) but also by electrochemical forces.  A complete identification of the properties of cohesive sediments typically involves twenty-four parameters (Commission of the European Community) and explains why the few studies referring to the transport and fate of cohesive sediment are site-specific rather than have a more fundamental nature. 
   
Contamination: The problem of excessive sediment loads is exacerbated in the Pacific Northwest as a significant amount of the cohesive material found in stream beds and banks is contaminated, thus affecting the stream water quality and ecology.  The sorption of these contaminants in the structure of sediments could alter the degree of their cohesion and subsequently affect the rate of re-suspension and exposure of benthic organisms to contaminants and the pathways for redistribution of pollutants within the aquatic ecosystem.  In order to quantitatively understand and predict the transport and fate of contaminated sediments during large floods on rivers, the resuspension and erosion properties of sediments at high bed shear stresses are needed.  Since most of the contaminants are associated with fine-grained sediments, knowledge of the origin and properties of these fine-grained sediments is also important.  A study was conducted to investigate the role of turbulent highly energetic episodes on the transport of cohesive sediments; identify the soil particles to source location, soil type, and their pathways and examine the impacts of metals associated with cohesive sediments on benthic invertebrate communities.  The findings of the study enabled the development of more strategic erosion-control programs than what are currently available and assisted communities and agencies to prioritize erosion protection zones important to fish and benthic populations.