The Canals of Venice

Venice is known as the "City of Water" due to the fact that it is situated inside the Venetian Lagoon. The city itself is composed of  127 small islands  that are premeated by 183 canals, varying greatly in length from as small as 26m to as long as 4km.

The Venetian canals are described using two technical terms. By definition, Canal is used to refer to a larger channel that connects two larger bodies of water. Using this definition, only a few of the canals in Venice are actually considered canals by definition.

In comparison, the word Rio (pl. Rii) is used to define any smaller channel that does not serve as a major connection between bodies of water. This word is used to reference the smaller inner-canals of Venice.

Prior to the 1990s, there was no standardized reference system to name and define the boundaries of the canals in Venice. Students from Worcester Polytechnic Institute working at the Venice Project Center (VPC) became the first to address this issue by officially definining the canal names and defining their boundaries through the use of segementation. By assigning a set start point and end point to each canal, the VPC was able to officially document the location and length of each canal in Venice, enabling them to be named. Through this, the intersections of the canals were also defined as their set endpoints. This system was adopted by the City of Vence, representing an important legacy of the VPC's efforts.

The map below depicts the name assigned to each canal. Click on each point to display the data.

The following map depicts the canal segments, click on each segment to view its identification code.

The Canals around Venice provide two indispensable functions for the city as both a means of waste disposal and transportation.

Throughout the city's history, Venice's canals have been used as a source of waste removal. Due to the currents in the canals, waste could be placed into the canals and then flushed out into the Venetian Lagoon, keeping the city clean. The city later improved this system by developing a system of brick tunnels, known as gatoli that directy connected points of waste collection to the canals, enabling the waste to naturally and efficiently be flushed into them. 

This waste removal method was effective due to its use of the natural resources present in the Venetian canals. When waste was dumped into the canals, it would be picked up by the currents, causing it to spill out into the Venetian Lagoon. Due to the importance of this process, the hydrodynamics of the Venetian Canals have been heavily studied in order to understand the most effective points of waste removal in the canals. The map below illustrates the hydrodynamics in the canals.

When a canal in Venice was identified as being stagnant, working against the flow of the natural waste removal, it was filled in by the government to create  Rii Terà . The government filled-in a total of 50 canals to form Rii Terà throughout the city's history.

Long term, it became apparent that the canals were not a sufficient source of waste disposal, especially as other cities began to develop modern sewer systems. The Venetian government attempted to address this through the creation of a sewer system. However, the canals still continue to hold their original function as the the primary mode of waste disposal in the city.

The canals also serve as the primary mode of transportation in the city of Venice, acting to facilitate the transportation of people, goods, and services via boats.

Before the development of bridges enabled people to travel by foot, the canals were the only method of transportation between islands, making them an essential piece of the city's economy.

In early years, people traveled through the canals on rowboats or gondolas. However, as technology has continued to evolve, motorized boats have come to dominate the canals as they transport people and goods.

Despite the fact that the canals of Venice generated through natural means, they have frequently been altered and reinforced in order to maintain them over the years. With Venetians relying on the canals as a means of transportation and waste disposal, the canals have gradually become damaged, eroded, and deteriorated over time. 

The canal walls are primarily constructed with two materials: brick and Istrian stone. In addition to building the basic structure of the canals, the canal walls also serve as the foundation for many buildings in Venice, making their materials even more critical. The non-porous Istrian stone is used instead of brick at the base of buildings because it does not corrode in water. Brick, meanwhile, is used more widely within the canals as it is relatively inexpensive and easy to acquire. However, brick is much more susceptible to being damaged by frequent exposure to water.

Sedimentation is a never ending process in the canals, which leads to the periodic need for dredging to remove the excess mud that accumulates on the bottom of canals. The sediment does not just precipitate to the bottom as soon as it is unloaded into the canal, but rather it floats to the bottom with a certain rate of precipitation which depends on what the suspended solids are made of.

Due to this, dredging must occur frequently to compensate for the rate of sedimentation in canals. Dredging is performed to keep all of the canals at least 2m deep at all times. This number was determined using two factors: the depth of the gatoli (120cm) and the depth required for boats to travel through the canals at the lowest tide (50cm).

In order to facilitate the dredging process, students from Worcester Polytechnic Institute developed a coding system for the canal segments, specifically used for maintainence purposes.

If the canals do not get dredged properly, sediment will build-up, blocking gatoli and fognature (sewer outlets) and preventing the removal of waste products. As a result of this blockage, sewer pipes rupture, weakening the mortar that holds the bricks of the canal walls in place. When prolonged, or combined with external factors such as moto ondoso (boat wakes), this instability can result in the formation of large caverns, or holes, within canal walls.

The following articles and websites were used as a source of reference for this StoryMap.