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D. S. McCulloch

Publications and source records attributed to D. S. McCulloch.

29 records · Page 2Linked to original sources
USGS1980

Single and superimposed bedforms: A synthesis of San Francisco Bay and flume observations

Tidal currents with maximum depth-averaged velocities ranging up to 250 cm/sec have generated ripples, two- and three-dimensional sand waves, and upper flat beds on the floor of central San Francisco Bay. Determination of the hydraulic conditions under which the observed beds exist, indicates that the bed configuration at any point in the bay is a function of the local velocity, sediment size, and depth. The bay observations, for flows up to 85 m deep, were combined with shallow-flow observations and a single set of bed-phase boundaries was determined for the combined data. Critical shear velocities calculated for the transitions from ripples to sand waves and from sand waves to upper flat beds, in flows tens of meters deep, are within 10% of critical shear velocities observed for the same transitions in flume flows only tens of centimeters deep. Comparison of bedform sequences suggests that, for flows up to tens of meters deep, beds of 0.25–0.50 mm sand respond to increasing flow velocities by forming ripples, two-dimensional sand waves, three-dimensional sand waves, and flat beds. At any constant depth, equilibrium sand waves increase in height and migration rate as flow velocity increases. The wavelength and maximum height of both two- and three-dimensional sand waves increase with depth also, but migration rates decrease. Because the maximum size of both kinds of bedforms varies with depth, classification schemes based on size arbitrarily separate genetically similar bedforms. In the bay, in contrast to flumes, sand waves having the largest height-to-depth ratios occur in relatively coarse sand. Tidal and seasonal velocity fluctuations are interpreted to be more destructive to finer-grained sand waves, because in finer grain sizes sand waves are stable at a relatively narrow range of velocities. Ripples, sand waves, and upper and lower flat beds are commonly superimposed on larger bedforms. Small bedforms can exist in equilibrium on the larger bedforms because the large bedforms generate boundary layers in which the small bedforms are locally stable. The distribution of small bedforms superimposed on larger bedforms reflects lateral and vertical variations in shear velocity in flow over large bedforms.

California↗
USGS1972

Drift of surface and near-bottom waters of the San Francisco Bay system, California: March 1970 through April 1971

The San Francisco Bay system is a complex estuary in which there is an interplay between natural chemical and physical processes, and changes resulting from the works of man. The bay is used for recreation, water-borne commerce, fishing, domestic and industrial waste disposal, and esthetic pleasure. Because some of these uses are competitive, it is desirable to adequately predict the impact of man's activities on this natural system. The reliability of such predictions will be strengthened by long-term observations directed toward understanding the natural processes occurring in the bay. This study is a compilation of one aspect of the U.S. Geological Survey's continuing investigations of the San Francisco Bay system.

California↗