A very wide stream ran into the East River between 106th Street and 107th Street, according to Viele's Water Map. One source of the stream came from the west side of Manhattan, and the water flowed to the east side near McGowan's (or McGowns) Pass, which was the pass used by the Kingsbridge Road to cross the low rocky cliffs that rose above 106th St at the time.
The images below show the stream as it was in 1776, as seen by the British. The first image is the whole map for context, and then the next is just a small cropped section to see the detail of the stream itself. The bottom of the map is at about 110th Street. (This was an area of Manhattan that saw a great deal of fighting during the first part of the Revolutionary War; the official title of this map is "A map of part of New-York Island showing a plan of Fort Washington, now call'd Ft. Kniphausen with the rebels lines on the south part, from which they were driven on the 16th of November 1776 by the troupes under the orders of the Earl of Percy. Survey'd the same day by order of His Lordship by C. J. Sauthier.")
Near the bottom of the map, "McGowan's Pass" is marked. This was a key passageway for Revolutionary War troops, and George Washington's men kept a lookout for the British from the higher ground north of 106th Street. The Parks Department has more information on McGowan's Pass on one of their excellent historical signs.
I am having a hard time corrolating the British views with Viele's Water Map of the same area; is the watercourse shown on the British map merely the northern extension of what is shown on the Viele map? If so, then it must have hooked East just past the bottom of the British map. The southern extension of the stream, which connects to other sources and flows to the East River, will be for a seperate post.
I have seen no traces of these streams on the surface of the modern city. There is also little trace of the challenging McGowan's Pass Road, which was described as late as 1893 as "wild and precipitous." However, there is a 5-foot diameter sewer underneath 106th Street east of Central Park, and there is an 8-foot by 12-foot sewer underneath East 110th St, both of which were built in the 1870s; was the stream re-routed through one of these sewers?