CAIT project no.: CAIT-UTC-067
Fiscal Year: 2015/2016
Rutgers-CAIT Author(s): Robert Miskewitz, Ph.D., Patrick Szary, Ph.D.
External Author(s): Scott Douglas, NJDOT
Sponsor(s): USDOT-FHWA, New Jersey Department of Transportation
The study of cohesive sediment erosion is important for decisions regarding the maintenance of harbor systems and their infrastructure. Cohesive sediments are defined as sediments that form flocs whose characteristics differ from those of individual particles. This cohesion may result from chemical properties of the sediment and eroding fluid (Berlamont 1993) or biogenic stabilization (Grant and Darborn 1994).
Unlike the erosion of larger, noncohesive sediment particles, for which critical shear can be predicted using Shield’s Diagram, the erosion of cohesive sediments is often difficult to predict. Understanding bed sediments’ potential for erosion is important for the prediction of scour and the filling in of channels. It is also valuable for situations in which contaminants are found within the sediment bed, as the fate and transport of contaminants correlate with those of the sediment.
The goal of the project was to critically review existing literature to access currently available devices, the identification of areas of improvement for future designs, and the outline of a new-generation cohesive sediment erosion measuring device.
The results of this investigation shows that several devices exist for the measurement of cohesive sediment erosion upon which there are great opportunities for improvement. Most significantly, the availability of technologies such as laser Doppler velocimeters and bed mapping systems would allow for the noninvasive measurement of key parameters directly in the field. The introduction of such instruments to the framework of existing flume devices would allow for greater accuracy in determining a relationship between bed shear stress and suspended sediment concentration. Direct measurement of the flow profile by the LDV would erase the potential for error where flows were previously estimated. Acoustic bed mapping technology has already been successfully utilized in the NIWA-II flume to noninvasively measure the erosion process (Aberle et al. 2004, Debnath et al. 2007). However, the integration of more advanced technologies, whether laserbased or acoustic, has the potential to improve accuracy and resolution in measurements.
The development of the proposed device is realistic and achievable, and would enhance the understanding of cohesive sediment erosion.