The San Carlos Canal (), also known as the Maipo Canal, is an irrigation and water supply canal in the eastern part of Santiago, Chile. It diverts water from the Maipo River into the Mapocho River and is about long.

Proposed since the colonial period and first contracted in 1772, the canal took decades to complete because of engineering errors, funding shortages, and the wars of independence. It was finished under the Sociedad del Canal del Maipo, a private association of irrigation-rights holders founded in 1827, which still manages it. Its construction is regarded as one of the major engineering feats of colonial Chile, and a colonial-era bridge on an older section of the canal was declared a National Historic Monument in 2014. Although the city has grown around it and its role in agriculture has diminished, the canal still irrigates farmland and also carries stormwater from eastern Santiago.

Course The canal takes its water from the Maipo River at an intake (bocatoma) at La Obra, in the commune of San José de Maipo. The intake has been damaged by floods on more than one occasion: a sudden rise of the Maipo destroyed the intakes of the San Carlos and Eyzaguirre canals in 1902, forcing the Maipo Canal Society to rebuild both, and high flows caused serious damage to them again in January 1942. Sand traps (desarenadores) along the canal capture the sediment carried by its water. The canal passes through or borders seven communes, six of them urban: Puente Alto, La Florida, Peñalolén, La Reina, Providencia, and Las Condes. Near Avenida Tobalaba it receives the surplus flow of the Ramón Creek, which is carried by a canal of the same name, and it ends at the Mapocho River opposite the Costanera Center.

Only part of the canal's water is discharged into the Mapocho. The remainder crosses beneath the river through a siphon and continues as the El Carmen Canal (canal El Carmen), which irrigates northern Santiago.

History Early attempts

Santiago lies in a fertile valley between the Mapocho and Maipo rivers, but the slope of the terrain made it difficult to bring water to some areas and to turn their dry, unirrigated land into farmland. The idea of a canal to take Maipo water to the lands south and east of the city dates to the earliest Spanish settlers, and early layouts are traced back to 1588, but a series of proposals in the 18th century failed to produce results.

The first documented attempt to build a canal linking the two rivers was made in 1742, but the site chosen for the intake was too low and lacked sufficient slope. In 1766 Juan Garland, an Irish military engineer in the service of the Spanish Crown, concluded that the original layout was unworkable. In 1772, amid droughts affecting Santiago, the project was revived and the contractor Matías Ugareta took charge. He opened part of the canal and named it for King Charles III of Spain. The work was suspended when the leveling was found to be faulty, and the cabildo of Santiago lost the funds it had advanced.Diego Barros Arana. Historia general de Chile, volume 7, Editorial Universitaria, 2000, pp. 168–171.

Cavallero's project On 28 April 1796, Ambrosio O'Higgins, on the eve of leaving to govern Peru, ordered that construction of the canal be undertaken in earnest. His successor as governor of Chile, the Marquis of Avilés, decreed on 28 November of that year that a commission be formed to study the project's feasibility. The commission, which included the engineer Agustín Cavallero and the architect Joaquín Toesca, delivered its report on 30 December.

Funds for the works were provided under Governor Joaquín del Pino in 1799. The following year Cavallero drew up plans based on a new scientific survey, and Martín Calvo Encalada was appointed unpaid superintendent of the project. Cavallero prepared seven plans. His design called for a channel wide at the top, wide at the bottom, and deep, with a gradient of for every from the intake. It also called for intakes with protective works, aqueduct bridges over the El Peral ditch and the Zanjón de la Aguada, and three bridges over roads the canal would cross. The planned length was about , and the works included excavation, lime-and-brick and lime-and-stone masonry, paving, embankments over vaults, and ramps.

Revised route and independence-era delays In 1802 Cavallero was sent to Panama, and the surveyor Juan José de Goycoolea, a disciple of Toesca, replaced him, assisted by Jerónimo Pizana. Goycoolea and Governor Luis Muñoz de Guzmán proposed a more direct route, starting from an irrigation ditch built earlier by the Jesuits, which roughly halved the budget. Of Cavallero's project, only the aqueducts and bridges were kept. Goycoolea chose the site of the intake and began the definitive works, but financial problems halted them between 1804 and 1811. The works were restarted in 1812 under Joaquín Gandarillas and Domingo de Eyzaguirre, but were suspended again when José Miguel Carrera withdrew the 200 laborers working on the canal to join the patriot forces. Carrera is also credited with resuming the works with public funds during the independence period.

Progress was very slow during the wars of independence. Once independence was consolidated, Supreme Director Bernardo O'Higgins ordered the works to continue under Eyzaguirre, whose efforts allowed the canal to be partially inaugurated on 20 August 1820, the feast day of Saint Bernard and O'Higgins's birthday.

Transfer to the Maipo Canal Society Facing a lack of funds, the government of Ramón Freire transferred all its rights in the canal to the holders of irrigation rights, who were also the owners of the main estates south of Santiago. On 5 July 1827 they constituted the Sociedad del Canal del Maipo under Eyzaguirre, who presided over it until his death and oversaw the repair of the canal and the completion of a network of smaller canals. By the summer of 1829 the canal was complete and water was reaching the estates and farms around Santiago. Over the 19th century, the Society's network of canals irrigated about 90,000 hectares (220,000 acres) of farmland, transforming the landscape of the southeastern part of the valley.

Present day Management and irrigation

The canal is still administered by the Sociedad del Canal del Maipo, which describes itself as the oldest private organization operating in Chile. Around 1920 the Society's network of canals was estimated to total about and to irrigate roughly 90,000 hectares of the Santiago valley. The canal's role in agriculture has since declined as the city has expanded; as of 1998, it and its branches irrigated about 15,200 hectares (37,600 acres). The Society reports that more than half of the canal's has a service road alongside it.

The canal is also an important collector of stormwater from the eastern part of the city. It has also had to be accommodated by subway construction. When Santiago Metro's expansion of Tobalaba station, where Line 4 begins, was presented in 2016, officials noted that the works would pass beneath both the canal and the Line 1 tunnel. The expansion opened in July 2023 with new entrances and an underground link, running under the canal, to the Mercado Urbano Tobalaba complex.

Heritage The Colonial Bridge on the Old San Carlos Canal (Puente colonial en el Canal San Carlos Viejo), also known as the El Peral bridge, is in the commune of Puente Alto on Avenida Tobalaba, between the La Frontera neighborhood and the Ciudad del Este condominium. It was built in 1805 as a vaulted structure of lime-and-stone masonry, brick, and other stone, a material widely used in Chilean construction in the late 18th and early 19th centuries. It lies in a ditch that formed part of the canal's original course and is one of the complementary works planned by Cavallero. It was built on the site of an older bridge used to move cattle from Argentina via the Portillo de Piuquenes pass and by Jesuit missions. Neighbors began pushing for its protection after recognizing its value in 2011, and submitted a proposal to the National Monuments Council in September 2013. The council approved it in October, and the bridge was declared a National Historic Monument by Decree No. 194 of 27 June 2014.

Urban integration and concerns

Communes along the canal have tried to incorporate it into green and recreational spaces. In 2010, for example, La Reina announced plans for a linear park and bicycle path along it.

Safety and sanitation have been recurring concerns. As late as 2012, residents in several of the communes it crosses reported a lack of fencing along the canal, accumulated trash, and rats.

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