Production and Abundance of Macro-Aggregate Bed Clasts from Moderately Consolidated Cohesive Beds and their implications for Sediment Management

Flume based research has demonstrated that large (greater than 1mm), high water content mud aggregates can be eroded from cohesive beds and transported in bedload. Studies have also documented these types of mud clasts preserved in the lithologic record. However, questions pertaining to the abundance of muddy bed aggregates and the physical properties that result in their production remain largely unaddressed. New flume experiments were conducted on materials from numerous sediment management project locations across the United States. Image analysis of eroded sediment particles demonstrated that macro-aggregated (greater than 250 microns) mud clasts were commonly produced in moderately consolidated sediment beds (1.2 g/cm3 -1.5 g/cm3) with water content above the plastic limit. These macro-aggregates commonly accounted for more than 20% of the total eroded sediment mass. Physical properties commonly associated with cohesive behavior were evaluated for correlation to bed aggregate production and size. Clay content of the sediment bed was shown to have the greatest correlation to both macro-aggregate size and abundance.