While the fecund Reserva Ecologica is located on the northern side at the mouth of the Riachuelo, the southern side is seemingly its opposite. Both, however, are the result of a major industrial city pushing into a silt laden estuary; the two faces of Janus. The south side is known as Dock Sud. It is the main petrochemical port and largest port in Argentina by operated tons. In addition to gas and oil it supports containerized shipping as well as sand mining operations. The port began in 1888 as a swampy, low-lying terminus to the Southern Railway which was British owned and operated until nationalization by Juan Peron in 1948. The port was constructed as a public entity which it remains today- its shipping channels and bulkheads are maintained by the provincial port authority while the storage, unloading, and manufacturing facilities are constructed by the tenant companies.
There is pressure on the port to expand in the future, especially its container and petrochemical operations. In addition, sediment dredging and the disposal of contaminated sediment is a significant cost to the port and a major area of concern for the residents in the densely populated surrounding area. Each year the port must dredge approximately 1,100,000 cubic meters to maintain their facilities at the required 10.4 meter depth. Fully one third of this is considered heavily contaminated, coming from the Riachuelo. The other two-thirds (740,000 cubic meters) is dredged from the exterior of the port, mainly the entrance channel (Canal Sud) which connects Dock Sud to the trunk line in the middle of the Rio de la Plata. While the clean sediment can be disposed of at sea, the contaminated sediment dredged from the Riachuelo and interior of the port must now be either treated or confined. The issue is one of murky jurisdictions- the federal constitutional amendment mandates that the environment must be protected, the port is part of the Province of Buenos Aires, and much of the pollution in the port comes from the autonomous district of the city of Buenos Aires.
The sediments of the Riachuelo-port complex offer a fascinating and terrible situation. The objective of this project related to the port will be the disposal of contaminated sediments. The Riachuelo and Dock Sud are inextricably linked by geography, hydrology, the shared industrial history, and they share in the ambiguous and contentious jurisdictional morass. This situation can be read through the common link that ties all of these themes together- sediment. Sediment pours down the Riachuelo, 640,000 cubic meters per year, half of which is dropped out in the port, the other half of which continues down out in to the Rio de la Plata. All of it is considered heavily contaminated, affecting the lives of people nearby and the port’s operational costs.
The industries and urban settlements polluting upstream raise the sediment disposal costs of the port considerably. Additionally, the pollutants from the port itself are flushed back in to low-lying neighborhoods during storm events and floods. Given the projected expansion of the port within the next 20 years, deeper channels will be needed. This will in turn require more dredging each year, a fact which projects future dredging of contaminated sediments to increase to 500,000 cubic meters annually. Currently no dredging is done in the Riachuelo until it reaches the port zone that begins at the Exolgan logistics center. This fact is evident in aerial photos and geo-soundings of the Vuelta de Rocha turning basin; it is no longer used and currently holds approximately 16 feet of contaminated sediments. This sediment is then dredged and disposed of in the Yarara disposal facility on the eastern edge of the port next to the Rio de la Plata. The facility is poorly constructed and filling up quickly. It’s protection dike of 3 meters is subject to overtopping and wave battering and needs to be reinforced and safely closed.
The 2009 report on stormwater drainage for the Riachuelo basin noted that due to the high levels of contamination in the sediments, which would be dislocated and possibly released by dredging, a 1995 report recommended that no dredging occur. However, this is being reconsidered due to necessities of using the canal for navigation and recreation (p. 134).
The cost of the treating the 320,000 cubic meters of contaminated sediments is approximately ten times that of confining it (50 million to 6 million). This cost would increase with additional dredging needed for channel deepening. In addition, it is possible to reuse contaminated sediments as fill material for new port constructions if the disposal facilities are properly constructed. For Tierra Plastica I am proposing a constructed near-shore disposal facility (see diagram above) to be constructed for confinement and use for new port facilities. This proposal draws from and adapts the conclusions of the “Sustainable Management of Contaminated Sediment in Puerto Dock Sud” report by Kay Croonen of TU Delft/U of Buenos Aires.
This construction, named “Camalote” on the map below, will allow for the Yarara facility to be properly reinforced, protected from storm events, and closed, and for 90 hectares of territory to be reclaimed for port expansion. The construction may be created from geotubes filled with mined sand, lined with local “tosca” clay, and reinforced with rip rap of construction and demolition rubble. By providing a place for the contaminated sediments and logistical support in their transport, and allowing ACUMAR to concentrate funds on prevention of further contamination and the installation of sewer and industrial infrastructure, the port will limit the amount of time they need to pay for the disposal of contaminated sediment.
The remediation dredging will be carried out by multiple proposed tram dredges (number to be determined) and will continue for 5 years. Further remedial dredging will likely be needed in the future due to the high number of industries and neighborhoods throughout the Riachuelo basin. A system of monitoring will be needed to ensure the sediments are not contaminated beyond acceptable levels- if they can be maintained in a state clean enough to allow future interior port dredge spoils to be disposed of at sea then port operational costs could be reduced by up to 10 million dollars a year.
The Yarara site has an estimated capacity of 2,460,000 cubic meters. It was estimated in 2008 to have only 200,000 cubic meters left and is likely now full or close to capacity, even with compaction due to dewatering. The Camalote site will provide an estimated 10,000,000 cubic meters of capacity. This will allow for storage of 1,000,000 cubic meters of dredge spoils from capital dredging in the Riachuelo, and provide capacity for confinement of contaminated spoils for the next twenty years. At that point, institutional controls instigated by municipalities, agencies, and businesses through ACUMAR should be fully operational allowing for source control of pollutants.
However, given the dispersed nature, both temporally (spread over 200 years) and spatially (throughout the basin and spanning multiple jurisdictions) of the pollution sources, including residences, businesses, and industry, any future design should prove robust enough to mediate common pollutants.
After the contaminated sediment is dredged and confined in the Camalote- or confined in place within the Riachuelo- and the new design depth obtained for the Riachuelo, maintenance dredging will be needed. By confining the contaminated sediments so that they don’t contaminate groundwater or get flushed in to the city with sudestada floodwaters the health of the residents of the surrounding area will be greatly improved. In addition, many plants and animals that currently suffer ill effects from the heavy metals and volatile organic compounds will have more space to grow and establish healthy ecological communities.
Regarding the future channel of the Riachuelo itself, the idea of “design depth” and “channel” needs to be rethought, considering that the future use primary uses of the Riachuelo will not be heavy industrial shipping but municipal transit, remediation, recreation, and light industry such as composting. A monitoring system and catchment system must be developed to ensure that future remediation- likely to become necessary as hundreds of years of contaminated sediment make their way downstream- can be undertaken as part of a functioning industrial/recreational ecology within the city.
+ Where will the sediments be transferred from the tram dredge to the Port Authority?
+ How long will the remedial dredging take place?
+ What kind of ongoing dredging will occur after remedial dredging is finished?
+ How will the sediment monitoring system function?
+ How will the sediment catchment system function?