ANTHROPOGENIC LAND CHANGES AND SEDIMENTATION RESPONSE IN TWO NEW YORK CITY TIDAL STRAITS

Detailed surface mapping and examination of historical records have shown how sedimentation in urban rock-bound estuary-tidal straits responds to channel changes and landfill operations that reduce the tidal prism. In addition, this study helps explain the landward origin of coarse facies, found in another study, at the northern part of New York Harbor. The Harlem-East River tidal straits connect the Hudson River Estuary, Long Island Sound and New York Harbor. Discovery of coarse facies in the Harlem River is an anomaly because only finer sediments are available from the Hudson and Long Island Sound. In addition, a mass of coarse material at the north end of New York Harbor has been shown to not have a Hudson, or an Atlantic origin. The only remaining possibility is that it was somehow transported down the East River.

Examination of the historical record suggests a solution to this quandary. In the past, coarse sediment from crystalline rocks in Westchester were transported southward by Tibbetts Brook into the Harlem and East Rivers and then into New York Harbor. This continued until the construction of the Harlem Ship Canal in 1897. That construction, plus the filling in of Tibbetts Brook, cut off supply of coarse crystalline sediment into the Harlem-East River complex. However, relict deposits of this sand exist today in the Harlem River. Another major source of crystalline sediment was from "Jerome Creek", now extinct. Yankee Stadium is located on the delta of that former waterway! Land extension in the low tidal current regime of Wards and Randalls Islands, resulted in the deposition of fine sediments between the Harlem and East Rivers.

The mass of coarse sediment at the north end of New York Harbor is essentially a relict tidal delta formed before the construction of the Harlem Ship Canal and the filling in of “Jerome Creek” in the early 20^th century. Recent mapping has shown that tidal currents are now reworking this coarse material and are moving it up estuary along the eastern side of the Hudson, at least as far as the George Washington Bridge.

This study has added new information on the effects of anthropogenic shoreline changes accompanying urbanization in New York City. It has also indicated that there are three, not two, sources of the sediment in New York Harbor.