Schuylkill Canal Glossary of Terms
, by John Urbanski, 9 min reading time
The glossary of terminology of the structures and features of a canal. Definitions of parts of the Schuylkill Navigation.
Arm: A short length of canal directly off the main canal.
Aqueducts: A bridge for carrying a canal over streams, gullies and roads. They can be built of stone, concrete, wood or iron. The Abutments can be of masonry or wood trunks. Aqueducts are larger than culverts.
Basins: Natural irregularities in the landscape and the need for loading areas result in wide places along the canal. Basins allow for loading docks, for turning boats around, and act as small reservoirs above locks. Above locks, the larger surface area of a basin allows the lock to be filled while producing a minimal drop in the level of the canal above.
Canal System: An artificial waterway constructed for navigation, irrigation, or water power.
Canalized: To convert to a canal. Refers to modified river or lake.
Coping Stones: The top course of stone on a masonry structure such as the top of lock walls or aqueduct parapet walls. Typically they are larger and well dressed.
Culm: Coal refuse (also described as coal waste, rock, slag, slack, coal tailings, waste material, rock bank, culm, boney, or gob) is the material left over from coal mining.
Culverts: Are smaller than aqueducts. They are channels to carry water under a canal. Most culverts are single arched stone structures.
Dams: Dams are used to create reservoirs. They are also used in river navigations to create the river pools used between locks. Some canals paralleling rivers have dams and pools in the river to supply the adjacent canal. Early dams were wooden cribs (boxes) filled with stone and covered with a wooden sheath. Some of these early dams are still in service, with a concrete cap. Later, in some cases, a masonry dam was built just down river from the original dam, submerging the original dam in the pool above. Others were built with masonry. More recently, dams are built with concrete, or concrete with steel gates.
Docks: Canals need docks to allow boats to come close to the edge for loading and unloading. On towpath canals, docks are usually on the berm side (opposite to the towpath) keeping the towpath clear for towing. Docks are often equipped with warehouses for the storage on goods in transit. Some of these warehouses are on the very edge of the water and have hoists to allow goods to be directly moved between boats and upper floors. In other cases, cranes are provided for freight handling. On the coal canals, chutes were used at the loading points to rapidly fill canal boats.
Doubled, paired or twinned locks: Doubled locks. Locks can be built side by side on the same waterway. This is variously called doubling, pairing, or twinning. The Panama Canal has three sets of double locks. Doubling gives advantages in speed, avoiding hold-ups at busy times and increasing the chance of a boat finding a lock set in its favour.
Dry-docks: Regularly, it is necessary to perform maintenance on canal craft. For this purpose, dry-docks are provided along the canal. These are chambers with a gate to the canal where a boat can be floated in and then be isolated from the canal. Once the chamber is closed off, a valve is opened draining the dry-dock into a lower level of the canal or into a nearby stream. Often, a dry-dock is large enough to hold several craft at once.
Feeder (Feeder Canal): Feeders are used to bring water from a reservoir or river pool to the canal. Often, the feeders are made navigable and serve as a branch to the main canal. Feeders enter the canal system at or near a summit level.
Fish ladders: The construction of locks (or weirs and dams) on rivers obstructs the passage of fish. Some fish such as lampreys, trout and salmon go upstream to spawn. Measures such as a fish ladder are often taken to counteract this. Navigation locks have also potential to be operated as fishways.
Gates: At either end of the lock are the gates. Many locks have miter gates at each end. These gates pivot around the end next to the lock wall and meet with a mate at the center of the lock forming a “V” pointed upstream when closed. In the closed position, the gates also seal against a miter sill on the lock floor. The “V” formed by the pair of gates causes water pressure to wedge them closed and transfer forces through the gate to the hinge forcing it into the lock wall.
Gate Recess: The cavity left in the wall of the lock to receive the lock gate when they are open.
Guard Locks: Where a canal crosses a river at the same elevation or joins a river at a dam, there is a need for protection of the canal from flooding of the river. This is often accomplished with a guard lock to allow movement between the canal and the river even if the river rises while controlling the flow into the canal. Often when the river is not in flood, the gates of the guard lock are left open.
Impounding basins (desilting basin): The Schuylkill River Desilting Project was instituted in 1945. A basin formed by earthen embankments/berms to hold sediment filled river water. As the coal silt settles from the water, a waste water weir is used for releasing the clear water.
Inclined Plane: An inclined plane is a type of cable railway used on some canals for raising boats between different water levels. Boats may be conveyed afloat, in caissons, or may be carried in cradles or slings.
Level: The portion of the canal between two locks.
Lock: A gated chamber that allows boats to move from one level of a canal to another. Essentially, a water elevator. A typical lock consists of a chamber with gates at both ends: a boat enters through the gates at one end of the lock; the gates are closed; water is added to or released from the chamber through valves until it reaches the level at the other end of the lock; the gates at that end are opened; and the boat continues on its way.
Miter Sill: A raised step against which a canal lock gate shuts
Paddle: Paddles are attached to the lock gates, used to open and close the gates to allow water in or out. Raising or lowering the water level.
Prism: The man-made channel that carries canal water. Called a prism because the top is wider than the bottom.
Reach: The distance between two locks.
Reservoirs: The heart of any canal system is water. This is especially true of summit canals, which must have an adequate supply to the summit level to allow locking in both directions. To supply water during the dryer months, canals usually include reservoir systems in the neighboring territory. These systems can be quite elaborate and extensive.
Rise: The rise is the change in water-level in the lock.
Slackwater Pool, Slack Water Pool: The water behind a dam is called a slackwater pool. The pools must have enough depth for barges to travel between locks at the dams. There were towpaths along the banks of the pools. The Norristown dam created a slackwater pool extending over four miles upriver to Catfish Island.
Sluice: An adjustable door/gate which enables water flow to be controlled.
Snubbing posts: Snubbing a boat to keep it from hitting the downstream gates. Note the rope wrapped around the snubbing post.
On horse-drawn and mule-drawn canals, snubbing posts were used to slow or stop a boat in the lock. A 200-ton boat moving at a few miles an hour could destroy the lock gate. To prevent this, a rope was wound around the snubbing post as the boat entered the lock. Pulling on the rope slowed the boat, due to the friction of the rope against the post.
Spillways and overflows: For a canal to operate properly, it is necessary to maintain the water at a constant level. But rainfall, either into the canal or into areas draining into the canal can result in too much water. To control this, spillways are included to allow this excess water to leave the canal without overflowing the banks and causing damage.
Stop Gates: Where canals have a long level between locks, it is often desirable to be able to close off sections of the level for maintenance or in the event of a bank failure. This is accomplished by a stop gate, which may pivot from the bottom of the canal or the sides or can be a guillotine overhead structure. Another approach frequently used where the canal narrows to pass under a bridge is a stop groove where timbers can be manually inserted. Stop gates are also provided where canals diverge from or cross rivers so as to be able to isolate the canal from the river in case of flood or for winter drainage.
Stop Locks: When variable conditions meant that a higher water level in the new canal could not be guaranteed, then the older company would also build a stop lock (under its own control, with gates pointing towards its own canal) which could be closed when the new canal was low. This resulted in a sequential pair of locks, with gates pointing in opposite directions
Swell or swelling: A swell was caused by opening suddenly the paddle valves in the lock gates, or when emptying a lock. To help boats traveling downstream exit a lock, the locksman would sometimes open the paddles to create a swell, which would help "flush" the boat out of the lock.
Towpath: A path alongside a canal used by horses or mules towing boats. The mules would have pulled the boats with a towrope covering about 20 miles a day.
Weir (Waste Water Weir): A man made structure that allows excess water to leave the canal system (overflow), while maintaining a constant operational level. Waste water weirs are also part of impounding basins used to discharge clear water as the coal silt settles out.
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