|dc.contributor.author||Young, Robert Alexander||
|dc.coverage.spatial||Buzzards Bay, MA||
|dc.description||Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September, 1975||en||
|dc.description.abstract||Erosion processes involving fine-grained marine
sediments were studied by using an in situ flume to erode
undisturbed bottom sediments on the sea floor in Buzzards
Bay, a shallow marine embayment off the Massachusetts
coast. Tte muddy sea floor in that area is characterized
by a deposit-feeding infauna that reworks the sediments.
Observations made with the in situ flume suggest
that erosion resistance of compacted bottom sediments
is up to twice as great as the erosion resistance of
biogenically reworked sediments. Estimates of erosional
bed shear stress from the in situ flume experiments
are similar to estimates made during this study of bed
shear stress developed in near-bottom tidal currents.
It is inferred that erosion by the in situ flume produces
reasonable estimates of bed shear stress necessary to
erode undisturbed bottom sediments on the sea floor.
Buzzards Bay muds were redeposited in a laboratory
flume and eroded after various periods of reworking by
the deposit-feeding organisms contained in them. Other
Buzzards Bay mud samples were treated to remove organic
matter, and the erosion resistance of flat beds of these
sediments was also investigated in a laboratory flume.
The surface of a biogenically reworked bed after
two months was covered with mounds, burrows, trails, and
aggregates composed of sediments and organic material.
This bed was similar in appearance to many of the beds
eroded by the in situ flume. The two month bed eroded
at an erosional shear stress similar to the erosional
shear stress necessary to erode the in situ Buzzards
Bay muds (0.8 dynes/cm2 ) . Beds biogenically reworked for
shorter periods had high values of erosional shear stress,
up to twice that of the two month bed.
The bed shear stress necessary to erode flat beds
of Buzzards Bay sediments increased as the concentration
of organic matter in the sediments increased. Deposit-feeders
were absent in these beds, and the mode of deposition
was kept uniform, so the increase
resistance with increase in organic content is considered
a reliable indication of sediment behavior, and not an artifact of experimental conditions.
During the in situ experiments, lee drifts were
created behind resistant roughness elements on the sea
floor. A brief study of lee drift formation in the laboratory
suggests that the formation of lee drifts from
fine-grained sediments can be predicted to take place
when the body Reynolds number of the resistant roughness
elements is below a critical value.||en||
|dc.description.sponsorship||The Office of Naval
Research supported this research and provided
salary support through grants to the Woods Hole Oceanographic
Institution and the Massachusetts Institute
|dc.publisher||Massachusetts Institute of Technology and Woods Hole Oceanographic Institution||en||
|dc.title||Flow and sediment properties influencing erosion of fine-grained marine sediments : sea floor and laboratory experiments||en||