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Figure 5.1. Index map showing areas studied during the first phase of the Hudson River Benthic Mapping program (1998-1999).

shells are 1,000 to 5,500 years old, but live oysters were found in the Tappan Zee and Haver-straw Bay during sampling in 2001.

2. Anthropogenic deposits are common in the Hudson River, and include numerous obstacles (some of which are ship wrecks), debris fields, Revolutionary War battlements, partially to fully infilled cable crossings and dredged channels, and linear bands of scour and deposition associated with bridge footings.

3. Sediment waves from 5 cm to3m high characterize the channel. Sand waves are dominant in the Kingston-Saugerties and Stockport Flats areas. The largest sand waves are found in the river channel off Tivoli Bay. All sand waves in the tidal Hudson River are affected by tidal flow and many sand waves show downstream migration. However, sand waves in some areas show net upriver migration -demonstrating locally varying flow conditions. We estimate the rate of sand wave migration in some areas to in excess of 10 my-1. Sediment waves also characterize several areas of overall muddy sediment, especially in the Tappan Zee and near Newburgh.

4. Most tributaries to the Hudson River have distinctive, generally elongated coarse-grained deposits at their mouths which extend both north and south, indicating that sediment deposition has been modified by tidal flow. These deposits can extend over five kilometers (km) along the river margin, as is the case for the Moodna and Wappinger Creeks.

5. Within the Tappan Zee region recent sediment accumulation is restricted to an abandoned dredge channel, tributary mouths, and the channel bend.

6. Although live zebra mussels are found in many of the sediment samples in the Kingston-Saugerties and Stockport Flats regions, they are concentrated at the mouths of tributaries and close to bedrock outcrops. No live mussels are recovered from areas of sand waves where the riverbed is more mobile.

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