The treatment of cohesive sediment is one of the last elements of sediment transport that is addressed almost entirely from an empirical standpoint. The primary objective of this research is to improve our understanding of the basic mechanisms involved in the re-suspension process of cohesive sediment and to examine the role of different soil parameters and contaminants on the re-suspension process with changing flow conditions. Subsequently, sediment entrainment formulas to predict the erosion rate of sediment as function of soil properties and the applied bed shear stress are expected to be obtained. These formulas are greatly needed for sediment erosion prediction, especially in the occurrence of floods, because most of the existing models are limited to low flow conditions.

The proposed investigation consists of two components. The first component will require the collection of field data. For this purpose, Rock Creek, located about 60 miles northwest of the Washington State University (WSU) campus near Spokane, Washington, has been selected. Rock Creek is overlain by mostly brown clay silt alluvium deposits. Field measurements at Rock Creek will enhance our understanding of sediment and contaminant transport in rivers, since the data will provide useful information about the properties of the undisturbed sediment and their correlation to the erosion rate (laboratory experiments by their very nature deal with disturbed sediment). By using isotope tracers, the source of the re-suspended material will be identified. Laboratory tests, the second component of this study, will take place at the Albrook Hydraulics Laboratory of WSU and will simulate the erosion process in Rock Creek for reconstructed and aged cohesive sediments under extreme flow conditions. Data corresponding to flood conditions are difficult to obtain from field studies, and thus, the performance of these experiments will be a vital component of this research effort as this information is not currently available in the literature. By coupling the results from laboratory and field tests, the complete re-suspension properties of in-situ surficial sediments will be approximately determined.

Results will be published in the refereed literature and will be presented at conferences. The proposed investigation will provide support for one M.S. student and at least one undergraduate student. The students will be involved in all aspects of the project: field data collection and analysis, laboratory work, and analytic work. In addition to the work directly supported by the contract, the Rock Creek field site will be a "gathering place" for undergraduate and graduate classes, where demonstrations and hands-on sessions will be provided to students. It is expected that this collaborative effort will be the start of a long-term research program related to the transport and fate of contaminated-cohesive soils. The findings of this research will provide the foundation for follow-up submissions to major funding sources.

Principal Investigators:

Thanos Papanicolaou Department of Civil and Environmental Engineering, Washington State University, apapanic@wsu.edu

Rollin Hotchkiss Department of Civil and Environmental Engineering, Washington State University, rhh@wsu.edu

Michael Barber Department of Civil and Environmental Engineering, Washington State University, meb@wsu.edu

Richelle Allen-King Department of Geology, Washington State University, allenkng@wsu.edu