Ps. Hill et al., IN-SITU MEASUREMENTS OF PARTICLE SETTLING VELOCITY ON THE NORTHERN CALIFORNIA CONTINENTAL-SHELF, Continental shelf research, 14(10-11), 1994, pp. 1123-1137
As part of the Sediment TRansport Events on Shelves and Slopes (STRESS
) program, a remote optical settling box was deployed on the northern
California continental shelf. The device operates by isolating a volum
e of sediment-laden fluid from the environment and then monitoring its
sedimentation behavior with a transmissometer. Results show a bimodal
distribution of suspended sediment during low-energy periods on the s
helf that reflects the size distribution of bottom sediments. The coar
se mode sinks at 0.026 cm s-1 (22 m day-1) and the fine mode settles a
t 0.0025 cm s-1 (2 m day-1). Between one-quarter and two-thirds of the
total mass resides in the coarse mode. Roughly one-quarter is in the
fine mode. The remainder sinks too slowly (<0.0015 cm s-1 or <1.3 m da
y-1) to be resolved during the 18-h measurement cycles. Greatest uncer
tainty in assigning mass to the various settling velocity classes come
s from sensitivity to ill-constrained particle geometry of the convers
ion from light attenuation to mass. The device failed during higher en
ergy periods, probably due to penetration of fluid into the box. Compl
ete isolation of the fluid from the environment would improve the perf
ormance of settling boxes in energetic settings.