Unruly Sediments

In the curve along the Thames where the river meanders near Greenwich, latticed metal cuts orange-brown across the moving line of the water’s edge. Inclined and vibrating, the overhead structures convey sediments dredged from United Kingdom’s coastal waters, some of which fly off, get stuck in grids meant to catch them, and fall onto the concrete and bricked footpath below. Finer particles are caught up in the high-frequency whirr of the screening machinery, a surround not continuous enough to become imperceptible.

This scene is a regular work day for those tending the machines, the heaps, and the dredge vessels. And y/our work here? Breathing dustily. Danger: deep slurry. The shrub sea buckthorn grows in a clump through a layer of dispersed sand against the burnt umber wall of the aggregates plant. On the other side lies the heap of the rest.

heap

Marine aggregates dredging was formalized as an industry during the twentieth century. Whereas capital dredging includes excavating ports, deepening channels, and land reclamation and maintenance dredging involves clearing accumulated sediments from ports and channels, marine aggregates dredging describes the extraction of sediments from the seabed, often for use in construction. However, in the turbidity created by moving sediments and corporate interests, these distinctions can become blurred.

How can we attend to sediments—their movements, forms, and categorizations—through and beyond colonial and capitalist logics and logistics? In allegiance with unruly particulate matter, how might we swerve from the ways we have been given to “know” sediments?

This essay weaves critical analyses of marine aggregates dredging across multiple scales with poem fragments gathered from notes made on repeated walks alongside Angerstein and Murphy’s Wharves between 2023 and 2024. This poetry experiments with mirroring, revealing, and destabilizing the aggregate heap of textual reproduction.

When Greenwich Peninsula was plotted and keyed for the first series of Ordnance Survey maps in 1805, it was a marshland, shaded with waves. Beneath today’s concrete, London’s river edges are made up of chalk, clay, and alluvium, deposited by shallow seas, glacial outwash, and shifting floodplain.

Where the aggregates plants at Angerstein and Murphy’s Wharves stand now, the map reads “Over Brickfield.” When London was being built up during the nineteenth century, brickmakers would remove the topsoil of a field, excavate clay or brickearth (a loam or silt covering the clay), mould and fire the earth into bricks, and then re-level the field to build on. The name “Over Brickfield” refers to what was scraped from the earth where seas used to be and made into constructive materials. Pre-metric bricks were shaped and sized based on what a hand could carry. Increasingly mechanized through industrial capitalism and maritime imperialism, construction materials became stacked, stackable, and standardized.

These materials were scraped from areas that are currently seas as well as areas where seas no longer exist. Out beyond the Thames estuary in the North Sea, trailing suction hopper dredgers drop suction pumps to the seabed and pull water and sediments into the hold. In glacial periods when sea levels were lower, rivers and beaches deposited sediments that remained relatively immobile when re-submerged. Does the geological term “deposited” make sediments appear already available for extraction?

Once the sediments have settled in the dredge hopper, water and finer particles are released back into the sea. These processes of extraction and release disturb and churn up oceanic habitats, re-suspend sediments in turbid plumes, leak contaminants, and alter wave and current systems. Dredging sites (known as the “Area Involved”) are licensed by the Crown Estate, which owns the seabed twelve nautical miles from the coast and the mineral rights in Britain’s territorial waters.

Loaded up, the dredge vessels travel up the Thames estuary along the tidal river, discharging bits of licensed seabed to the riverside works of private building materials companies. On Greenwich peninsula, Angerstein Wharf is operated by CEMEX, and the nearby Murphy’s Wharf is operated by Tarmac. Angerstein Wharf is named after the eighteenth-century Lloyds marine insurance underwriter and art collector John Julius Angerstein, who had links to the slave trade.

The UK marine aggregates industry, regulated by the British Marine Aggregates Producer Association (BMAPA), provides 22 percent of the UK’s sand and gravel supply for construction—a figure that is likely to grow with the depletion of on-land (quarriable) resources. As coastlines erode due to climate change, rising sea-levels, and the long-term impacts of sea defense infrastructures, sand dredged from ancient underwater beaches is rainbowed onto shorelines in a process known as “beach nourishment.” Bottom-feeders are dispersed and metabolized in shorelines and buildings where chloride ions rattle.

aggregate

In 2023, the UN Environment Program and Global Resource Information Database in Geneva launched Marine Sand Watch (MSW). Using ship movement data, MSW visualizes the activity of dredging vessels as they carry out sand mining, land reclamation, and maintenance dredging. As a user of the platform, when you click on a country, its Exclusive Economic Zone (EEZ) appears as a fluorescent green outline 200 nautical miles from the country’s land border, superimposed onto the pale blue of ocean waters. Click on the UK and its maritime border extends outwards across the North Sea, meeting the nautical line of the Netherlands: a juridical and material membrane, requiring negotiation.

Layering the computational filters (screening sediments, [dis]aggregating data) in the North Sea, the platform can show how many square kilometers of sea are being dredged for sand. Add more layers: how many vessels are dredging, their type, the year the dredging took place. Click on an individual ship and the flag it was sailing under appears: Great Britain, the Netherlands, Luxembourg, Belgium, Cyprus. Some ships sail under “flags of convenience,” where ship owners register a vessel in a different nation’s ship register, often enabling them to avoid tax, labor laws, and environmental regulations that might impede the smooth flow of grit and gravel.

Sweep across the platform to Singapore, a city-state in an ongoing process of expansion through land reclamation with extracted sand. Despite being on the other side of the globe, many of the flags are the same, suggesting that it is not only geologic matter but also power that is sedimented in extractive economies and ecologies. These flags represent the ongoing afterlives of maritime imperialism.

Dredging vessels also have their own behavioral ecology. They tend to move about the ocean’s surface in a distinctive way. Using a predictive algorithm trained on actual ship movement, MSW also hazily forecasts theoretical dredging activity. If you want to sift further into MSW’s data, you can select different filters, one of which shows “Sand Concessions – Likely.” This particular filtration system highlights, in an intermittent series of beige polygons, the areas of seabed “which have most likely been used to extract/mine sand over the period 2012-2019.” The helptext associated with the filter cautions viewers: “Note: Delineation of sand concessions is based on dredging patterns in the north sea [sic]. The algorithm is not yet tailored to other regions.” These predictions are sucked from the perforated guts of a machine-learning algorithm.

amber palette polygons (angular) in area involved

trackpad clickhold sweep stretch pinch h h extrapolated pebbling over reclaimed swampoutpostmegaport

How are these methods and knowledges derived from “dredging patterns in the north sea” and European conceptions of ocean space continually projected at a global scale through vectors of data? The algorithm has learned to read not only the information but also the forms of information it has been fed: centuries of recording European maritime vessels’ positions according to a spatiotemporal grid, territorial regulations of sediments as categorizable resource, and accumulations of granular knowledge as a set of scales and units. What counts as “data” exists in material relation to the specific sites of extraction where data are generated or, perhaps more accurately, built.

In MSW’s helptext, we can read a curious reflection between the actual processes of sand dredging and the data systems used to monitor and predict it: disaggregated and quasi-chaotic material formed from highly specific geo-biological relationships is extracted, filtered, and cleaned, to be eventually (re)constructed in “other regions,” an externalized elsewhere of both concrete and information. The forms of matter and knowledge amalgamate, blustered by what currents, salt, and friction above or below water can do to technologies of measurement over centuries, shell content altering what knowledges can be built.

granule

For sediments to be made constructive, they need to be knowable and amassable as categorizable units. When they get off the belts at the Angerstein Wharf aggregates plant, they are analyzed carefully. Unprocessed sediment heaps are cheap, labeled “ballast as dredged” (BAD) until they are screened, washed, and sorted by particle diameter according to various standardized scales:

Sediment type	Particle diameter (European Standards)	Particle diameter (Wentworth scale)	Notes (BMAPA Glossary)
Gravel	>4mm	2-64mm	coarse aggregates
Sand	0.063-4mm	0.063-2mm	fine aggregates
Silt	0.002-0.063mm	0.002-0.063mm	considered a contaminant; weak structural qualities; to be actively avoided
Clay	<0.002mm	<0.002mm

In 1922, American geologist Chester K. Wentworth published “A Scale of Grade and Class Terms for Clastic Sediments.” This scale, which is the basis for industry standards, emerged from Wentworth’s research into the effects of water transport on cobbles and pebbles, corroborated with a survey of US and UK-based geologists (notably identified as “men”).

In the process of its formation, the scale is already shattering. Wentworth writes: “Strict uniformity […] will not fit the sediments as they occur in nature. Bowlders [sic], cobbles, and pebbles are rounded rock fragments, whereas most clay particles are angular, yet geologists will recognize that they all belong to a natural series. Likewise, bowlders and clay particles are not commonly of the same mineral composition but in spite of this fact they are the two extremes of the series of transported rock fragments.”

How does this “natural series” relate to territory, as a site of extraction and construction? Where does the unit meet the aggregate in capital’s calculative and accumulative logics? These aggregate(d) units are seabeds upturned in piles and simultaneously regularized and lumped.

Thinking with the geophysical projection of sovereignty via imported sand in/on/under Singapore, William Jamieson identifies sediment’s “promiscuous statelessness . . . its granular transitions between phases, expressing characteristics of matter without lingering in any single state” as the exact material modality that makes it “liable to capture and subversion by the capitalist production of space.” But the sediments are unruly, turbid, troublesome. Sediment is also oppositional to colonial, capitalist, and logistical productions of space. If gravel, sand, silt, clay, are matter in a mode of “promiscuous statelessness,” then how do we, as promiscuous and stateless enemies of capitalism, form disaggregated allegiance with it?

Even Wentworth admits the heap of his gritted language (which has come to be a standardized scale) is always slipping and collapsing: “By an excessive multiplication of terms it would be possible to make a classification in which each term was specific as to size of particle, shape of particle, lithologic character, and other characteristics. Such a scheme would be highly artificial in many of its categories and seems to the writer impracticable in the present state of knowledge.”

The more unruly water and geologies are, the more they are infrastructured through knowledge systems and logistical operations that seek to (re)locate stuff (buried beaches, sand gapers) in economies of value and the continual making of urban space. Conversely, the more that waters and geologies are infrastructured, the more unruly they become?

icedragged flux pockets

stillish subwater-

folds saltier than

could stand (on)

un-nesting impermeable

categorying micro-

porously flaked

trolleys blended clanged pilings lapse

stuff of tide laps pilings frict corrode

                                                         

to heaps from units of now the scoop of

                                                         now heaps dead slow chuck out dispersal

  of arid salt spray few hours or days ago

  was benthic bed as a biogenic ooze

    heaped here for whelks collapse in +

the lapse of yanktime hopper gravel 20mm

   heaps held in walls happen as walls

Outside the sand-matted spikes of steeled fence, a mound formed from repeated unintended dropping collapses inwards on its own shelled axis. Whorled and turbinate, in the shells are benthic whelk-drilled holes.

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Featured image: Sediment heaps and overhead conveyor belts at Angerstein Wharf on Greenwich Peninsula, London, UK. Photo by Katy Lewis Hood, 2023.

Acknowledgments: Thank you to the Turbid Circulations writing group (Therese Keogh, Miriam Matthiessen, Madeleine Collie, and Solveig Qu Suess) for discussing earlier iterations of this writing, and wider conversations around oceanic geographies and extractive infrastructures. Special thanks to Therese for accompanying Katy on one of the trips to Angerstein Wharf, for casting shells together, and bringing their thinking around settler colonialism and dredging in Awabakal and Worimi lands into conversation with waters and sediments in London.

Jac Common is a quasi-academic and writer. Their work is grounded in encounters between organic and inorganic worlds through different forms of knowledge, story, and attention. Jac’s creative and critical work is published in several places. Website. Contact.

Katy Lewis Hood is an interdisciplinary scholar and writer based in London, UK. Katy’s creative and critical work considers how poetic practices attend to the durational effects of colonialism and racial capitalism on watery places and relationships. They are currently a Lecturer in Creative Writing at Queen Mary University of London. With Jac Common, they collaborate on Coneffluents, a poetic research project attuning to queer, anti-colonial, and nonhuman lifeways in wetland ecologies and infrastructures along the River Thames. Contact.