We start this set of readings with a brief review (from the 1972 edition of the Gross oceanography text) of the physical properties of sediment as they relate to sediment transport. The figures referred to in the text aren't included, but you will have some class handouts illustrating the relationship between particle size and current velocities needed to erode and transport sediment; you should look at these in conjunction with this reading.
The next reading (by Hill and Halka) provides a review of the spatial pattern of sediment types on the Bay floor and relates this pattern to the main sources of sediment and the way that sediment is transported from source to final resting place. Take a close look at the map showing the spatial distribution of sediment types. An online version in color is available also at
http://mgs.dnr.md.gov/coastal/sedpage.html
Make sure you understand what the major sources are, which way the sediments are moving, and how sediments are sorted into different textural groups in different parts of the Bay.
The third reading, by Schubel, considers the dynamics of sediment transport in the upper part of the Bay, which is dominated by flow from the Susquehanna. Schubel discusses sediment transport and sediment concentration patterns during high-flow periods (the "spring freshet") and during low-flow periods. He talks at some length about how sediment is scoured from the bay floor and resuspended in each tidal cycle, and he also talks about processes that cause suspended material to settle out of the water column (including flocculation, which he doesn't think is terribly important, and the role of planktonic organisms in ingesting suspended material, packaging it into larger particles bound together by mucus, and then excreting it as fecal pellets). A key topic that we will emphasize in class is the "turbidity maximum", which is related both to the effect of tidal-current resuspension of bottom sediments and to the two-layer pattern of net nontidal circulation. This in turn is related to the concept that the estuary behaves as a sediment trap, i.e. very little of the sediment supplied from whatever source ever escapes. This pertains not only to Chesapeake Bay as a whole but also to the tributary estuaries: each of them probably traps virtually all of the sediment that enters it, so that the tributary estuaries supply little or no sediment to the main Bay.
The fourth reading is a brief excerpt from a paper by Schubel and Pritchard. This excerpt discusses the importance of major floods with regard to the delivery of sediment to the estuary. Clearly we cannot understand sedimentation in the estuary unless we take these rare events into account.
The fifth reading is a workshop report from May 2000 about the influence of sediment from the Susquehanna River on Chesapeake Bay. The reservoirs upstream of the mouth of the Susquehanna have been storing sediment for many decades and they are nearly full; they have been trapping much of the total sediment that otherwise would have been reaching the Bay, and once they do fill the amount of sediment reaching the Bay may increase very rapidly. The workshop report explains much of the context of this problem. For our purposes, Appendix A (by Jeff Halka of the Maryland Geological Survey) provides a detailed discussion of the sources and disposition of sediment coming into the Bay and of the distribution of sediment types on the floor of the Bay. This is somewhat of an update of the 1989 reading by Hill and Halka.
Another topic not covered in this set of readings will be discussed in class if we have time: the effect of land use patterns on soil erosion and sedimentation rates. There is evidence that more sediment reaches Chesapeake Bay today than before European settlement, and hopefully we will have a chance to discuss the nature of that evidence.
Readings on estuarine sediment:
1. Readings in Adobe Acrobat (pdf) format:
Dredging and associated concerns: