Surveying the Erie




Finding the Level:  Maps vs Profiles

With canals, the route taken (map)... depends upon the elevation of the ground (profile)

The Original Erie Canal had three high-spots.  Can you find them on this 1832 profile?

(larger images of both)

Each of those three high-spots needed a source of water that was higher than they were.
  Finding those sources was one of the most important jobs of the early surveyors of the canal.

Holland Land Museum, Batavia, NY

Early surveyor's transits like this one were used to lay out the course of the original Erie Canal  across New York State.  Though cutting-edge for their day,  these instruments were primitive by modern standards, and were prone to errors due to careless use and to rough handling (e.g. being carried on horseback). Even without errors, the task of finding a level route for a canal in that day was a daunting one. Transits were "line of sight" tools and New York State was a wilderness of trees then. Their succeeding as they did - when they did - was an amazing engineering feat.

An illustration - Consider the sixty-two mile level stretch between Rochester and Lockport in the western section: Remember:   WATER ALWAYS HAS TO REMAIN LEVEL If the bottom of canal was ONE FOOT too high, boats would run aground If the top was ONE FOOT too low, water would run over the towpath  Using a transit like the one shown above...      ...a "minute" of angle (1/60th of one degree) spans an inch at a distance of one hundred yards.  Suppose that the surveyor's transit that was used to tell the contractors where and how deeply to dig was off by just one minute of angle when they started the project westward from Rochester; and that the same error was applied over the whole sixty-two miles all the way to Lockport.  If uncorrected, that four-feet deep canal bed - along with its towpath alongside - would be ONE HUNDRED feet too high or too low by the time they reached Lockport!