HUDSON RIVER FLOODPLAIN CHANGE OVER THE 20th CENTURY

Detailed surveys of the Hudson River and its floodplain from the early 1900s, and high-resolution mapping of the same areas today, provide an opportunity to evaluate changes over the 20th century. This study uses GIS to quantitatively compare water areas and islands mapped by the United States Army Corps of Engineers in 1907-11 along an approximately 37-mile reach from Athens to Troy, New York, with the same features mapped in the early 21st century. The comparison shows a substantial decrease in the acreage of total water area (~ 30%) with secondary channels disproportionally affected (~ 70%). The number and total area of islands has also dramatically decreased: ~ 65% and ~ 85%, respectively. These changes primarily reflect the success of navigation improvement projects undertaken since the 19th century whereby the river has been transformed from a shallow, island-braided river in the study reach to a deeper, single-thread channel. Dredge spoils from the main channel were used to fill secondary channels and other backwater areas, with important implications for native aquatic species that rely on these areas for feeding, nursery, and rearing habitat. Restoring secondary channels is an opportunity to restore important habitats and environmental functions critical to the productivity of the Hudson River Estuary ecosystem.