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Mohawk River

Course

From its source in Lewis County the Mohawk River flows generally east through the Mohawk Valley, passing by the cities of Rome, Utica, Little Falls, Amsterdam, and Schenectady before entering the Hudson River at Cohoes, just north of Albany.

River modifications

The river and its supporting canal, the Erie Canal (a part of the New York State Canal System, called the New York State Barge Canal for much of the 20th century), connect the Hudson River and port of New York with the Great Lakes at Buffalo, New York. The lower part of the Mohawk River has five permanent dams, nine movable dams (seasonal), and five active hydropower plants.

The Schoharie Creek and the West Canada Creek are the principal tributaries of the Mohawk River. Both of these tributaries have several significant dams including the Hinckley Dam on the West Canada and the Gilboa Dam on the upper reaches of Schoharie Creek. The Gilboa Dam, which was completed in 1926 as part of the New York City water supply system, is the subject of an active and aggressive rehabilitation project.

History

The river has long been important to transportation and migration to the west as a passage through the Appalachian Mountains, between the Catskill Mountains and Allegheny Plateau to the south and the Adirondack Mountains to the north. The Mohawk Valley allowed easier passage than going over the mountains to the north or south of the valley. As a result, it was strategically important during the French and Indian War and the American Revolutionary War, and a number of important battles were fought here. The fertile Mohawk Valley also attracted early settlers.

In the early nineteenth century water transport was a vital means of transport both people and goods. A corporation was formed to build the Erie Canal off the Mohawk River to Lake Erie. The canal cut shipping costs to Lake Erie by 95%. It also simplified and reduced the difficulties of westward settler migration.

The Mohawk Valley still plays an important role in transportation. Railroads followed the Water Level Route, as did major east-west roads such as US Route 20 and Interstate 90.

The Mohawk River Heritage Corridor Commission was created to preserve and promote the natural and historic assets of the Mohawk River. This commission was created by the NY State Legislature in 1997 to improve historic preservation along the river.

Flooding and Discharge

The Mohawk River has a relatively long record of flooding that have been documented back to settlement in the 17th century. The average volume of water that flows through the Mohawk is about every year. Much of the water flows through the watershed in the spring as snow melts rapidly and enters the tributaries and the main trunk of the river. The maximum average daily flow on the river occurs between late March and early April. For the period between 1917 to 2000, the highest mean daily flow is c. per second as measured at Cohoes, near the confluence with the Hudson. The lowest mean daily flow of per second occurs in that same time interval in late August. There is a long record of significant and damaging floods along the entire length of the river.
Because the river and its tributaries typically freeze in the winter, the spring melt is commonly accompanied by ice floes that commonly get stuck and jammed along the main trunk of the river. This annual spring break up typically occurs in the last few weeks of March, although there are plenty of floods that have occurred before or after this time. These ice jams can cause considerable damage to structures along the riverbanks and on the floodplain. The most severe flood of record on the main trunk of the Mohawk River was the spring break up flood that occurred from 27-28 March, 1914. This flood caused a tremendous amount of damage to the infrastructure because it was a spring break up flood with enormous amounts of ice. Ice jams of some significance occur about every other year.

The last major flood on the Mohawk was on 26-29 June 2006, during the Mid-Atlantic United States flood of 2006. Flooding was caused by a stalled frontal system that resulted in of rain across central New York and widespread flooding occurred in the Mohawk, Delaware, and Susquehanna watersheds. Across the state, this event caused over 227m in damage and resulted in the loss of four lives. This flooding was acute in the upper parts of the Mohawk watershed.

Geologic history

thumb|As the [[Laurentian Glacier retreated it blocked the outflow of Glacial Lake Iroquois. Instead of flowing down the St Lawrence Valley it flowed down the Mohawk River.]]

The Mohawk watershed drains a large section of the Catskill Mountains, the Mohawk Valley proper, and a section of the southern Adirondack mountains. All three regions have distinct bedrock geology, and the underlying rocks get progressively younger to the south. Overall, this part of New York is represented by lower Paleozoic sedimentary rocks that unconformably overlie the Grenville-aged (Proterozoic, here about 1.1 billion years old) metamorphic rocks of the Adirondacks. In the watershed, these rocks are only significant in the headwaters of the West Canada Creek. Much of the main trunk of the Mohawk River sits in Cambro-Ordovician carbonates (limestone) and Middle Ordovician sandstones and shales. The southern tributaries (Catskill Mountains) are underlain by a thin sequence of Devonian limestones that are overlain by a thick sequence of sandstones of shale of the Catskill Delta, which is also of Devonian in age. During the Pleistocene (c. 1.8 to 0.01 mya), the watershed was extensively modified by continental glaciation. As a result of glacial scour and deposition, the surficial deposits in much of the watershed are poorly sorted boulder- and clay-rich glacial till. During deglaciation, there were several glacial lakes that left varved clay deposits. Finally, in the final stages of deglaciation at approx. 13,350 years ago, the catastrophic draining of Glacial Lake Iroquois, a pro-glacial lake, was through what would become the modern Mohawk Valley. In this final phase of the geologic story, an enormous discharge of water caused local deep scour features (i.e. the Potholes at Little Falls), and extensive sand and gravel deposition, which is one of the key sources of municipal groundwater including the Scotia Delta, which is also known as the Great Flats Aquifer.