Dredge Landscape Taxonomies

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?"

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