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dredging

Dock Sud; to the left is the Exolgan container port, to the right is the Shell and YPF petrochemical facility; in the middle is the Canal Sur; to the far right on the edge of the Rio de la Plata is the Yarara confinement area for contaminated sediments; a tiny but noticeable breach is visible in the southern containment dike in the new cell; it is unclear if this cell is in use yet

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 action chart for the Tierra Plastic project shows the relationship of the Riachuelo to the port through sediment; in this case, the contaminated sediments are the instrumental aspect of the landscape, organizing the entire network around itself; the future Camalote disposal facility is indicated; capital dredging is shown in thicker lighter grey arrows, maintenance remedial dredging in darker with a darker arrow; the black boxes alongside the names of objects indicate their depth in relation to mean sea level

Objective

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).

Proposal

diagram above illustrates dredge volumes in Dock Sud port by year; diagram series below just above illustrates different disposal structures considered for the new Camalote site; a near-shore confined disposal site is chose as it offers the best combination of secure containment, reduced costs, and fill for new port facilities

actual and projected increases in shipping, by tons operated; though Dock Sud is currently Argentina's busiest port, it is expected to triple the number of tons moved in the next twenty years; most of that growth will come in containerized shipping, though petrochemicals will continue to grow as well

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 Math

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.

geotubes may be filled, lined with local clay, and reinforced with rip rap including construction rubble to create a secure confinement dike fo the Camalote site

Implications

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?

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aerial showing context and limits of dredging program and creation of publicly accessible Camino de Sirga along the embankments of the Rio de la Plata; for scale the highlighted portion of the Riachuelo canal is almost exactly 1.5 miles long

Tierra Plastica is understood to be taking place under the purview of ACUMAR, the river basin authority of the Riachuelo.  ACUMAR (Autoridad de la CUenca MAtanza Riachuelo) is a decentralized interjurisdictional governmental agency with capital funds.  River basin authorities have developed into a relatively common device for dealing with the issues of pollution, economics, and politics in watersheds that span jurisdictional boundaries (as most do).  ACUMAR is unique in that it has capital funds to implement its decisions and recommendations thanks to a billion dollar loan from the World Bank.

One of the few precedents for this type of organization is the Tennessee Valley Authority which built dams, reforested hillsides, and constructed roads throughout the Tennessee Valley during the New Deal years of the United States (it still maintains a capital budget today, albeit a much less ambitious one).  ACUMAR differs from the TVA in that it is not a centralized planning organization accountable to an executive office and built according to the engineering/systems model as detailed by technological historians David Noble and Thomas P. Hughes.  Rather, ACUMAR is both part of and made of a network of administrative and technical experts, with its executive council consisting of local, state, and federal officials who work closely with the heads of state agencies such as Environmental Agency and Education Agency.

The organization itself is ultimately responsible to a federal court in nearby Quilmes, province of Buenos Aires, Argentina and works in concert with various local and municipal groups, non-governmental organizations, and municipal governments.  The nation of Argentina is responsible to the World Bank for showing progress according to the approved environmental remediation plan that was used to secure the loan.

inside the norris dam, built by the tennessee valley authority; at the norris dam the river basin authority created a landscape that is a massive piece of energy infrastructure and a publicly accessible recreation area; people come to walk through the forest and swim in the lakes, as well as to enjoy the technological sublime aspects of the landscape

a TVA shovel at work on a roadway at the Norris Dam site; note the "TVA" inscription on the shovel; as a river basin authority with capital funds ACUMAR like the TVA has the ability not only to pay contractors to build infrastructure, but also has the ability to buy its own instruments and undertake long-term projects and implement maintenance regimes

ACUMAR is responsible for executing the Integrated Plan for Environmental Remediation (PISA, by its Spanish Acronym), which it does by operating along four lines of action:  institutional, remedation, industry, planning and infrastructure.  There are certain aspects of both the plan and the institutional structure that are instructive and will ultimately be internalized as assumed parameters for the project.

1.  Efforts are being made to control the pollution point-sources upstream, including the construction of new sewage treatment plants, fining businesses disposing of chemicals and objects in the river, and controlling stormwater runoff.  Nonetheless, a robust and local system is needed for containing and cleaning the detritus and refuse carried downstream in the water column

2.  The system of levees and bulkheads that protect the urbanized area from floodwaters needs to be enlarged and reinforced, especially to withstand the sudestada storm events that occur several times per year and when combined with rain upstream and high tide lead to widespread flooding in the basin.

3.  As of April 2011 57 sunken or inoperable boats have been extracted from the river between the Pueyrredon Bridge and the Avellaneda Bridge.  In addition over 70 vehicles have been excavated from the canal bottom and there are no more in this zone.

4.  The Camino de Sirga (35 meter wide towpath) has been cleared of obstruction and structures in a first phase up to Dean Funes Street, with a second phase underway to clear up to Pueyrredon Bridge.  It is being cleared and designated as public space.  Sections further upstream are also being cleared with the final intent to unify a 35 meter wide swath on either side of the canal for public access.

5.  Dredging is being considered by ACUMAR in coordination with Port Authority at Dock Sud.  There are still some working port operations near the mouth of the canal and the section from the Vuelta de Rocha to the Canal Sur is still maintained and dredged by the Port Authority.  Any material that is dredged from the RIachuelo would have to be treated as contaminated and a treatment and disposal site would be needed.

6.  Two non-governmental organizations are currently advocating for the dredging of the canal; one in the interest of cleaning the watercourse, the other in the interest of making it navigable for a system of municipal transit boats.

2011, ACUMAR removes one of the 57 boats sunken and abandoned in the Riachuelo

Conclusions for the design of the Camino de Sirga

+ The physical limits of the site are defined as the outer edge of the Camino de Sirga on either side of the canal and all the space between, beginning at the new Avellaneda Bridge and going to the Pueyrredon Bridge, as this is the section where ACUMAR has worked to clear the Camino de Sirga of obstructions.  From there to the Victorino de la Plaza Bridge the project scope will be limited solely to the watercourse of the canal, as this area is desired for navigation but it is unknown when the Camino de Sirga may be cleared here.

+ Any design must include a strategy for dealing with the floodwaters of the Rio de la Plata, especially those occurring due to sudestada weather events.

+ The design should include a system that allows for constant monitoring of water level, sediment elevations, and enable the intermittent sampling of water and sediment chemistry.

+ Retention and filtration of stormwater along the banks of the canal in the urbanized area is necessary to reduce flooding in the basin.

+ Any design needs to provide a system for the filtration of contaminants and objects.  Major infrastructural and institutional investments by ACUMAR will help alleviate the situation.  However, given the heavily urbanized context the design of the canal should not suppose that all objects and contaminants will be removed.

+ For the purposes of this thesis project it will be assumed that ACUMAR has decided in favor of some type of dredging for the Riachuelo Canal.  A treatment and containment site is needed and should be coordinated with the Dock Sud Port at the mouth of the canal.  Creating a canal that is navigable for both recreation and municipal-scale transportation is desired by community groups and being considered by ACUMAR.  For Tierra Plastica it will be considered a necessary and ongoing process.

A gold dredge in Nome, Alaska where a decade long gold rush occured between 1899-1909

The question is this:  which instruments and what dredging regime is most appropriate for environmental remediation of the Riachuelo, and what will the resultant canal landscape be?  Admittedly, identifying the specific actual dredger and regime to be used is outside the scope of this project.  However, be considering the different types of machines and the landscapes they create through the mobilization of sights, sounds, materials, and a whole host of equipments and their concomitant expertise, we can identify desired results and causal relationships with specific instruments.  This will allow us to speculate on the type of dredge instruments to be used, and how, and therefore test our thesis of landscape instrumentalism with a specific design proposition.

In their most basic incarnation, dredgers are simply machines used for underwater excavation.  Applications include the improvement and deepening of shipping channels and ports, land reclamation, excavation of minerals, and environmental remediation.  There are three basic types:  hydraulic dredges, mechanical dredges, and hydrodynamic dredges. All three types engage in acts of dislodging, lifting, transporting, and disposing; mostly of a slurry composed of sediments and water from the bottom of the targeted waterway.  Each dredger is an assemblage of equipments and instruments including barges, hoses, cutters, hydraulic arms, pumps, and engines to name a few.  In this way, discreet acts of dredging can be thought of as instances of accelerated geological processes.

Considered from a materialist perspective dredging can be a generative act; the machines, equipments and specialized knowledge of the operator enter into a sort of duel or partnership with the water- its currents, chemicals, and biologies- and the sediments with its silica, organic matter, and toxic compounds.  Dredgers are typically imagined as landscape-building machines, used for beach nourishment and building new islands, cutting deeper channels and widening shipping ports.  Landscape instrumentalism is interested in the ways that the act of dredging itself generates landscapes- the movement of the dredger, sediments, the knowledge of operators and fleeing of local schools of fish all swirl together to create a violent and dynamic processual landscape.

Landscapes of Dredge

mechanical dredge operation landscape- each object is labeled and the four main relations between objects are represented as actions that are numbered; the primary characters or instruments work to create a dynamic landscape-in-process

hydraulic dredge operation landscape

Dredging operations are paradoxical by their nature.  Conceived as a specific linear process outlined in the above four steps– dislodging- raising- horizontal transport- final placement– these operations are nonetheless part of a larger network of relations that feed back in to the newly created situation, often working to undo the original intentions of the dredging program; the channel begins to resilt due to the construction of steeper banks and exposing of destabilized sediments to still-active erosive currents.  Every act is a spicy mix of human intentions and hard-headed ecologies and geologies pushing against one another.  Because of this, discreet dredging acts are necessarily part of a larger regime of dredging that works over time to counteract or harness the larger forces at work- ocean currents, river flow, meteorological events, specific geology, and local structures.

A dredging regime must attempt to comprehend these relations that are external to the discreet dredging operation and counteract or exacerbate them through an extended account of time and space which transgresses the limitations of scope and scale established through accepted engineering science [limitations which are necessary to ensure that measured goals are met within acceptable means and methods].

Dredging the Riachuelo

Some Considerations:  Developing a dredging regime for the Riachuelo in Buenos Aires with the intended goal of environmental remediation presents its own specific demands that must be approached:

+ high levels of toxicity in the sediments from industrial activities including fecal coliform, chromium, copper, lead, zinc, and PCB’s

+ the bulkheads which protect the urban structures along the edge of the canal must be protected and reinforced

+ local meteorological events, especially the winter sudestada storms can raise water levels in the canal upwards of 12 feet

+ daily tidal fluctuations vary the water levels in the canal by 3 feet

+ ongoing port operations of the Puerto Dock Sud, including dredging of the boat basins and darsena sud shipping channel, at the mouth of the canal, and relocation of the sand mining operations

+ human settlements along the banks of the canal- neighborhoods will be visually and aurally impacted by dredge work, and dredge work will be impacted by the stormwater runoff and detritus that filter from and through these settlements into or along the canal

+ biological communities, such as local fish populations or hyacinth blooms will impact the ability of dredgers to work with the sediments and slurry targeted by their instruments (the cutterheads, buckets, barges, and pipelines and also the strategies and technical knowledge of the designers and operators)

+ existing objects sunken into the bottom of the canal, especially cars and boats.  These are the detritus of 200 years of industrial and urban use, often quite careless or intending to externalize negative outputs of industrial processes.  In the area between Puente Avellenada and the Darsena Sud it is estimated that there are 57 boats sunken in to the bottom of the canal recently extracted by the Argentine Naval Prefect with the collaboration of ACUMAR, the river basin authority

+ the clearing of the camino de sirga by ACUMAR.  The camino de sirga, spanish for “canal tow path”, is to be cleared of private constructions and opened for pubic access to the Riachuelo.  The camino de sirga is defined as a 35 meter setback on either side of the canal.

Sediments:  The Riachuelo currently transports approximately 320,000 m3 of sediment per year.  All of this is considered contaminated and much of it is dredged by the Port Authority of Argentina and confined at the Yarara disposal side on the river side of the petrochemical dock in the port.  Historical deposited sediments in the Riachuelo, all heavily contaminated, vary from 1′- 14′ feet thick.  When still maintained for port operations, the depth of the Riachuelo was 24′.

Because of the shallow depth of the Rio de la Plata, a trunk line is dredged from the sea up to the Parana River, with branches leading to Montevideo and Colonia in Uruguay, and the Argentine cities of La Plata and Buenos Aires; nearing Buenos Aires the dredge channel branches again; "Canal Norte" heads to Puerto Nuevo, "Canal Sud" goes to the Puerto Dock Sud at the mouth of the Riachuelo

the geology underlying Buenos Aires and the Riachuelo is a loess called "pampeano", with the margins of the city and the bed of the Riachuelo contaning much more fine-grained clay and mud; this type of soil in ideal coastal situations can be dredged effectively with a cutter suction dredge or a trailing hopper dredge because it does not consolidate to a high degree

Instruments:  The geology of the river basin suggests that dredging operations can be carried out most effeciently- the most amount of sediment can be moved with the least amount of effort- with a hydraulic dredge such as a cutter suction dredge.  However, a dredging regime also needs to consider:  safety of users and neighbors, noise, horizontal transport of sediments, mixing of soil layers, creation of loose spill layers, and dewatering or treatment method. 

Given the proximity to dense populations to the canal, the likelihood of encountering large voluminous objects in the sediments (such as cars and mopeds), the continual and extended need for dredging, the distance from a disposal site, limited disposal space on the banks for dewatering and treatment, the need for precise maneuvering, and the desirability of opening the canal to municipal navigation for reasons of tourism and transportation, the needed instrument would likely have an articulated arm with grab capabilities and be capable of maneuvering without a tug boat.

Conclusions:  A mechanical dredge will be fitted out and deployed in the canal- constantly making the canal landscape- size to be determined.  It will work on a yearly cycle that must be developed in consideration with strategies for stormwater and upstream siltation, flood events, adjacent urban populations, existing contaminants, noise pollution, river ecosystems, new contaminant sources, and containment and disposal of sediment.

This canal landscape will be a place of acceleration and deceleration.  The dredging regime will have the stated goals of:

+ removing, treating, and confining the contaminated sediments of the canal

+ making the canal and its banks open for municipal transportation at all times

+ maintain low levels of noise pollution in the canal and the immediate areas

+ reduce costs of maintenance dredging for the Puerto Dock Sud at the mouth of the Riachuelo

+ contribute to the re-development of health ecological communities within the canal landscape

+ contribute to the creation and maintenance of the camino de sirga  as a public, accessible part of the city

This dredging regime will be implemented in accordance with a larger project and program (which is currently being hatched).

the Prefectura Naval (Argentine Navy), alongside the river basin authority ACUMAR and the Environmental Ministry, pulls sunken boats from the Riachuelo and stacks them on the future camino de sirga; the question, of course, is "what kind of massive hulking floating-bridge-barge-type-thing is that?"