Techniques of terrestrial soil mechanics, modified to includein situ sampling using SCUBA gear, have shown differences in sediment mass properties between various reaches of the York River, a coastal plain estuary of southeastern Virginia, which are interpreted as delineating areas of sediment removal and deposition within the estuary.
Sediments found in the upper and lower portions of the estuary are similar in their mass properties. Both are “silty clays” and possess low unit weight and very high moisture content. middle estuary contains “silty clays” possessing high unit weight and lower moisture content. Shearing strength is lowest in the upper estuary, slightly greater in the middle reaches, and much greater in the lower estuary.
Deposition is believed to be proceeding rapidly in both upper and lower estuarine areas. The middle estuary appears to be a surface of sedimentary bypassing.
Sediment shearing strength must be considered when planning channel modifications. Current velocities which impose bottom shear stresses in excess of measured shear strength will initiate scouring. Design criteria should include acceptable velocities for given reaches of rivers undergoing modifications given a knowledge of mass property distributions.