*Oceanography 540--Marine Geological Processes--Winter Quarter 2001*
### Ocean 540, Winter Quarter 2000

Problem Set #4

**You do not have to turn this problem set in, if you attend the
Problem Set Workshop on Thursday afternoon, March 8. If you cannot
attend the workshop, please make alternative arrangements with me.**
- Consider a sediment bed consisting entirely of 30 um grains. How strong a current (as measured well above the seabed) would be required to transport the grains? To produce a concentration profile above the bed such that the concentration at 50 cm was exactly twice that at 100 cm? How does the Stokes
settling velocity of the particles compare to the horizontal velocity in
the bulk flow?
- During a "benthic storm" observed in the deep sea, particle concentrations reached 3 mg/l at 2 meters above the seafloor. If these were 5 µm particles, what would be the rate of change in particle number concentration due to turbulent shear? How long would you expect these particles to remain in suspension after the storm event, i.e., what is the characteristic time for their return to the seabed?
- Consider this observed velocity profile (in an estuary):

Height above bed (m) |
Fluid velocity (m/s) |

6.4 |
1.19 |

5.7 |
1.16 |

4.8 |
1.13 |

4.3 |
1.11 |

3.6 |
1.08 |

3.0 |
1.03 |

2.3 |
0.98 |

1.7 |
0.92 |

1.1 |
0.82 |

0.5 |
0.65 |

Use the linear form of the Law of Wall to evaluate the roughness scale and the shear velocity. *If* the roughness is due to grain roughness, what is the size of the grains?

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