Friday, July 1, 2011

Sediments: Here Comes Everything

Today’s post on sediments is the final excerpt from the Field Guide to Urban Industrial Canals which can be seen and downloaded for free from Issuu.  If it interests you check it out, and if you find it particularly helpful, interesting, or weak in a particular area we would love to hear about it.
[the rio de la plata estuary; uruguay is on the left and argentina is to the right, with the city of buenos aires in grey; the estuary carries massive sediment loads from the heart of the continent- the basin includes five national capitals and Sao Paulo;  the rio de la plata and its delta (in the foreground) is formed by the confluence of the rio parana and the rio uruguay]

[the sediments of rio de la plata add to argentina's coast line every year just south of buenos aires; here the petrochemical dock in 1927 at the mouth of the riachuelo, with the canal sarandi in the foreground; all of the watery area framed by the jetties in the center is now dry land occupied by the expanded port facilities; image source]

The sedimentation process is one of deposition and accumulation.  In rivers it typically occurs in places where the current slows down.  In a pre-industrial river the main sediments are bits of clay and sand and pebbles from upstream that form beautiful sandbars and oxbows and influence the river’s course over time.  In an industrial river- one that has been canalized and is dredged and used for barge traffic- these pre-industrial sediments are mixed up into a frothy stew with all the industrial materials and wastes, as well as the runoff and suspended solids from the street gutters and sewer system of the surrounding city.  All of these substances tend to settle out along the bottom of the canal and have to be regularly dredged in order to keep the channel clear for barges and boats.

Dredging operations ceased for many canals sometime in the mid-twentieth century, usually around 1950, when the size of ocean going traffic became much larger and the canals weren’t able to easily be widened because of the constructions along their banks.  As the sediments piled up, the capacity of the water channel for moving water was seriously reduced and in some cases flooding problems are exacerbated as is the case in the Riachuelo in Buenos Aires. 

Continually dredging a canal where industrial operations have all but ceased is a difficult expense to justify when municipal budgets are tight, despite the flooding and environmental issues.  Once the canal begins to silt up, it becomes impossible for the neighboring water-dependent and water-enhanced industries (such as scrap yards, coal yards, steel mills) to use it; once all of the neighbors have turned their back on the canal, the falloff in water quality can be precipitous.  This suggests that, whenever possible, new uses for canals that require a navigable channel would improve water quality and might help reduce flooding and environmental problems.

Sediments on industrial canals inevitably contain serious substances that are harmful to many organisms, including humans.  For that reason they are often left “down there” below the surface of the water, where no one has to worry about them too much, unless you happen to live nearby.  Companies and governments usually have politically expedient reasons for not dredging the sediments- they are highly contaminated with toxic substances.  In addition to stirring up the pcb’s and heavy metals and tars that are mixed in on the bottom of the canal, the sediments that are dredged cannot be disposed cheaply- hazardous waste dump sites are incredibly expensive. 
[sediments along the gowanus canal, brooklyn, 2010]

[sediments along the riachuelo canal, buenos aires, mid 1930's; image source]

The sedimentation process occurs on the banks of canals as well, where tides, flood waters, street runoff, as well as people deposit all sorts of jetsam and flotsam.  This material is most often considered a nuisance- shopping carts are deposited at street ends, plastic bottles and old wood scraps find their way into the chain link fencing that edges many places along the canal.  While this material is mainly a nuisance and it is rather difficult to think of a possible reuse for it other than simply cleaning it up, the deposits are evidence of material eddies in the city.  The contemporary urban environment is like a highly regulated waste stream, with food and water and consumer goods coming in, being consumed, and then deposited and whisked out of the city- the municipal solid waste system.  Appropriate mobilization and management of this system is perhaps the key catalyst to any urban project.  The biological capacities of canals to consume human waste when properly managed, and their tendency to accumulate the trash that escapes the waste stream suggests they should be an area of focus for sanitation departments in cities. 

Specific sedimentation patterns could be strategically utilized- the canal is an eddy in the urban ecology of waste, transportation, and also everyday use.  They offer an alternative to the highly programmed recreational park, the commercial shopping mall, or the office park.  It is something of a no man’s land, and by providing simple access around the border and across its width, and finding a way to reduce the exposure to the toxic substances, entire ecosystems of local populations of plants and animals including humans would spring up along its banks.  Indeed, to a limited degree this already occurs and need only be encouraged in the lightest possible way to generate a fecund alternative to the overly programmed recreation park, the commercial shopping mall or street, and the office tower.  People and things might come here and to sit outside of the rushing city currents for a while, watching the sediments swirl by.
[the gowanus as brooklyn eddy]

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