Why the C&O Canal was built, and how a lock raised a boat eight feet

Men boarding a canal boat. NPS Photo / C&O Canal NHP.

A boat going upstream through a lock on the Chesapeake & Ohio (C&O) Canal had to rise eight feet, and the lock lifted it by letting in 90,000 gallons of water over several minutes. This article by Raisa Barrera, from the National Park Service, explains that mechanism and why the canal was wanted at all. The canal carried goods from near West Virginia and Western Maryland down to the former port city of Georgetown in Washington, DC.

Why Chesapeake and Ohio?

After the War of 1812, rising prices for agricultural commodities drew settlers westward in search of more fertile land. Western farmers shipped wheat and corn down the Ohio River to the Mississippi and on to ports where it was sold or sent on. The article says the Potomac was the only river on the East Coast that crossed the Appalachian mountain barrier, and so was considered the best route for Western trade.

As early as 1749 the Ohio Company of Virginia, a land and trading venture organized by prominent Englishmen and Virginians, set up trails and wagon roads through the upper Potomac River Valley. They linked it with the Monongahela River, a tributary of the Ohio, and with the area called the "Bread Basket of America." Joining the waters of the Chesapeake Bay and its tributaries to the Ohio River was the key to reaching those western crops.

Topographical map of part of Maryland showing relief by hachures, drainage, cities and towns, canals, the Washington Aqueduct, roads and railroads with mileage on the main survey line. Courtesy of the Library of Congress.

What a canal is

A canal is a man-made waterway built to carry goods and people by water from one place to another: a channel cut into the land, with water flowing through it. The C&O Canal was built alongside the Potomac so boats could pass through difficult terrain.

George Washington backed skirting canals, with locks and channels, to bypass the Potomac's five worst obstacles to transportation, the most serious being Great Falls. He gained support from Virginia and Maryland after he became a national hero in 1784. He died in 1799 before the project was finished. By the 1820s a proposal was made for a permanent canal along the river from Washington, DC, all the way to the Ohio River. The rights of the old Potomac Company passed to a new company incorporated by Virginia and Maryland, and the "Great National Project" began.

Cutaway of the canal bed, called the "prism" because the top was wider than the bottom. NPS Photo / Harpers Ferry Center.

How a lock works

A lock raises and lowers boats between stretches of water at different levels. Its distinguishing feature is a fixed chamber whose water level can be varied. It has three elements: a watertight chamber joining the upper and lower canals and large enough for one or more boats; two gate doors at either end, watertight when closed; and a valve that lets water in and out.

How a canal lock works: a lockkeeper uses the swing beam to open the sluice valves. NPS Photo / Harpers Ferry Center.

Going upstream. The boat enters through the lower gate, the doors close behind it, and it sits at the bottom of the chamber, needing to rise eight feet to reach the lock walls and the water level upstream. Each gate door has two small paddles at the bottom, linked to metal rods that run up the door and stick out the top. A crew member turns the rods with a lock key, which is essentially a giant wrench, to open the paddles.

Filling. The four paddles on the upstream gate are opened one at a time, and a total of 90,000 gallons rushes in over several minutes, raising the water until it matches the level upstream. The crew must steady the boat so the current does not crash it into the lock walls, either by steering with the engine or by using boat poles. While the levels differ, the upper gate cannot be opened because of the pressure on the upstream side; once water level and pressure are equal on both sides, the doors open and the boat continues.

Going downstream. The process is reversed. The boat enters a lock already full, the gates close, and the four paddles of the downstream gate release 90,000 gallons into the next level, lowering the boat eight feet. When the pressure is equal on both sides of the downstream gate, the doors open.

Locking through. NPS Photo.

Locking through, in five steps: the upper sluice valves open and the water in the lock rises to the level of the upstream canal; the upper gates open and the boat enters, then the upper gates and their valves close; the lower gate valves open and water drains out; the boat is lowered slowly as the water drops to the downstream level; the lower gate opens and the boat goes on at the lower level.

A film of the canal

The article points to a 12-minute Library of Congress video, "Down the old Potomac," with scenes of the canal recorded in 1917. The Library's summary says it follows a week-long, 180-mile trip on the canal through the Potomac Valley from Cumberland, Maryland, to Washington, D.C., and shows locks in operation, a mile-long hand-dug tunnel built in 1840, coal barges, Maryland farm country, Harpers Ferry and Great Falls.

A frame from the Library of Congress video "Down the old Potomac."

Sources

• National Park Service, Chesapeake & Ohio Canal National Historical Park, "The Power of Water: Transportation", article by Raisa Barrera (https://www.nps.gov/articles/000/the-power-of-water-transportation.htm), part of the series "The Power of Water"; rewritten in hubnx's own words.