Dredging of the Port of Fremantle’s Shipping Channels, 2010, Perth, Australia.
A continuous stream of shipping barges pass through the Mississippi River Delta, moving over 350 million tons a year through its three largest ports. Of those, the Port of South Louisiana alone stretches 87 kilometers along the Mississippi, and annually sees some 4,000 ocean-going vessels and 50,000 barges. It is the largest tonnage port in the Western Hemisphere, and the fifth-largest in the world. To maintain this logistical flow, channels — their size and depth determined by the needs of the international shipping industry — must be kept clear. No small task, due to the 200 million tons of sediment that are carried down the river every year. Much of this sediment is washed out to sea or deposited inoffensively along the banks, but a significant portion of comes to rest in industrially inconvenient places. In the Army Corps of Engineers’ (USACE) “Mississippi Valley” district, around 10 million tons of such sediment must be shifted each year. The channels are dredged, and refill, and are dredged and refill. It is to the processes that shape this landscape, and others like it, that we turn our attention.
Sisyphus Climbs the Hill
At its core, dredging is an excavation operation carried out at least partly underwater, with the purpose of gathering up bottom sediments and disposing of them at a different location. Dredging is “used to improve the navigable depths in ports, harbors and shipping channels, or to win minerals from underwater deposits. It may also be used to improve drainage, reclaim land, improve sea defense, or clean up the environment.” The most common purpose is to counter the forces of gravity and erosion manifested as clogged waterways or disappearing coastline.
Classic dredging operations treat dredge as a linear proposition. A dredging machine — typically a barge fitted with scooping (“mechanical”) or vacuuming (“hydraulic”) components — arrives at the site and begins collecting sediment. That sediment is transferred off-site via pipeline, barge, conveyor belt, truck, or some combination thereof. The sediment is then disposed of at another site, either through underwater dispersal, contained land placement in fields, pits and other receptacles, or the creation of new coastline.
The great irony of dredge is that dredging contributes to the acceleration of the very forces which it is intended to counter. As the rivers and coastlines where dredging occurs are dynamic, unstable environments, loosening and transporting sediment tends to further destabilize these landscapes, causing more erosion and siltation.
Dredging thus begets more dredging, and is situated within a wider network of anthropogenically-accelerated sediment handling activities and practices. In considering this wider network, we arrive at a more comprehensive understanding of dredge, which includes not only the act of removing underwater sediments and depositing them elsewhere, but a sprawling regime of practices which both exacerbate and mitigate the effects of anthropogenically-accelerated erosion. We invite you to consider these contemporary, leading-edge, and speculative practices as subjects suited to architectural intervention. These are the landscapes of dredge. Sisyphus is our patron saint.
Close up view of dredged sediment being pumped onto a manufactured marsh platform. Louisiana, East Timbalier Island.
A Tour of Sisyphus’ Domain
Dredge can be understood as a soft system at two levels. First, there are the techniques, technologies and tools used in the management of landscapes of dredge. This kind of softness might be described as operational softness.
The second order of softness is defined by the contemporary shift in dredging process from linearity towards feedback and cyclicality. Whereas operational softness is concerned with discreet instances of dredging, this is systemic softness, encompassing the entire set of interrelated processes and landscapes of the vast dredge cycle. At all scales — from a flimsy silt fence to regional dredge management plans — dredge is a malleable set of tactics responding to an ever-more affected terrain. The subject material of dredge — sediment and particles held in liquid suspension — is soft. So too, the working materials of dredge.
Anticipation and Flexibility
Silt Fence (Brett Milligan)
The expansion of dredge beyond barges in a river can first be seen in the proliferation of preventative techniques. Erosion control is anticipatory; for instance, vegetative erosion control involves planting to arrest the anticipated erosive action of water on slopes and stream banks. However, vegetation takes time to grow and many projects require a faster solution. For this reason, a variety of geotextiles have been developed.
On land, silt fences are installed prior to the commencement of new construction, anticipating the loosening of sediment. In water, turbidity curtains are placed around an area before dredging begins, to both arrest fluid motion into the dredge zone and to reduce the movement of suspended sediment out of the dredge zone. When flooding threatens to turn land into water, sandbags are deployed as emergency levees.
USACE Passive Dredge Collectors, in operation near Louisiana’s Biloxi State Wildlife Management Area.
One anticipatory technology which is even more directly linked to dredging is the Passive Dredge Collector (PDCs). Derived from submersible barges developed for naval transportation, PDCs are deployed to ease the process of maintaining shipping lanes in places where there is rapid accumulation of sediment. The barges are placed on the riverbed where a suite of on-board sensors allows remote operators to monitor the accumulating load. When they are ready to be harvested they rise to the surface through air ballast for retrieval and transport.
Many geotextiles are produced by TenCate, an international materials technology corporation. Perhaps their most striking invention is the hulking geotube. Massively-scaled hybrids of sandbags and silt fences, geotubes are designed to be filled with the slurry byproduct of a dredging operation. They have two major functions: temporary structure and material containment. The best deployments exploit both functions at once.
Geotubes and their applications. In the background, a worker stands by a Geotube placed near Barren Island in the Chesapeake Bay, during restoration work undertaken by NOAA.
When they are used for containment, dredged material is pumped directly into the tubes. Purified water seeps out of the porous walls while the remaining particles are processed for fill or topsoil. They are excellent for projects with limited settling areas including water treatment, aquaculture, and industrial lagoons.
Geotubes are also semi-permanent structures that can be easily inflated, deflated, and repositioned. They are made of flexible material, so they ooze and flow to conform to the shape of rough terrain. Their size and mass makes them very stable once deployed. Their applications include breakwaters, dams, shoreline protection, and island creation. They are highly adaptable and it is not difficult to envision treating their hulking, undulating form as an aesthetic feature to be championed.
Adaptability, Recycling, and Responsiveness
Adaptability is similarly displayed by cellular confinement systems, also known as “geocells”. First developed by the USACE to provide a way to lay roads quickly on unreliable terrain, they are composed of strips of material which, when pulled into tension and deployed, expand into honeycombs. The cells are then packed with material, such as sand, soil, stone, or plants. They are used for a variety of stabilization purposes including roads, slopes, channels, and retaining walls. In reservoirs and landfills they are paired with impermeable geotextile membranes to isolate the contents from the wider landscape.
Aerial Image of Poplar Island Restoration in the Chesapeake Bay, accompanied by the Army Corps of Engineer’s list of Beneficial Uses of Dredge for Engineering, Agriculture, Product and Environmental Enhancement Applications.
Located in the Chesapeake Bay, Poplar Island is a flagship example of the USACE’s beneficial uses of dredge. Working with state and federal organizations, the USACE has been placing dredged sediments from The Port of Baltimore’s shipping channels onto the island since the mid-90’s. This practice meets the Port’s immediate need for a dredge disposal site while symbiotically creates much needed habitats for fish and wildlife, at a time when such habitat is threatened due to sea level rise. Over approximately 18 years, 40 million cubic yards of dredge material will be placed here to create 1,140 acres of manufactured island.
One key characteristic of the transition from linear processes of dredging to more cyclical operations is the growing re-use of dredged material. Traditional dredge techniques rely on the availability of designated ‘disposal’ facilities (or landfills for sediment). As these facilities have quickly run out of storage capacity, creative recycling practices have emerged by necessity. The USACE has dubbed this the “Beneficial Uses of Dredge”.
The USACE’s extensive list of beneficial uses includes the creation of aquaculture facilities, construction materials (such as fill and topsoil), decorative landscape products (sculpture, cultured stone, etc.), beach nourishment and shore protection, berm creation, landfill capping, land creation and improvement, creation of fish and wildlife habitats, fisheries improvement and wetland restoration. Dredge is no longer approached as a problematic material to be disposed of as cheaply as possible, but as a strategic resource.
In many respects, the USACE is playing catch-up to the Netherlands, which have significant experience with dredge landscapes — as much of the nation is reclaimed land sitting below sea level. They now export their knowledge and technology through the Netherlands Soil Partnership.
Few landscaping organizations can operate at the global scale of the Netherlands Soil Partnership.
The unique geographic condition of the Netherlands led the Dutch to develop world class expertise in the legislation, science, and practical tools for combating soil contamination. Key areas include soil risk assessment, remediation technology, and purity control, all of which are essential to the practice of re-use.
Success in vanquishing domestic soil contamination has led to saturation of the market. Very little local soil needs remediation, leaving companies with expertise and capital and nowhere to apply it.
The Partnership is a public/private cooperative effort, which seeks to disseminate Dutch technical know-how to partner countries. In turn, new markets open for participant corporations. The result is technologies and practices – developed for a very particular need – applied to landscapes all across the globe. Whole geographies reshaped by Dutch expertise.
Consider the Sand Engine, a land creation technique currently under development. The project involves the strategic deposition of 21.5 million cubic meters of sand in the shape of a large hook projecting out from the nation’s coastline. Using existing patterns of wind, waves, and ocean currents, the formation will gradually distribute its accumulated sand along the coast. “‘Building with nature’ in this way will ensure natural sand suppletion, so that the coastline grows [and] will therefore help protect the coast and create new land for conservation and recreational purposes at the same time.” Once set in motion, engineers will no longer have to mechanically dredge sand from some other location to replenish the beaches every five years. The landscape will do it itself.
This responsive landscape is created through a combination of predictive foresight and intervention in formative processes. Responsiveness uses existing landscape forces for desired ends, rather than fighting uphill against such systems.
The process used in designing the Sand Engine is like forensic anthropogenic geology. The “computed morphological development” of the design is based on the integrated data of “wave fields, flow velocity fields, sediment transport fields, morphological evolution, sedimentation/erosion patterns, erosion of adjacent coastlines, necessary nourishment volumes and evolution of the dune area.” Yet even with this dauntingly complex foresight, the strategy still has an operational uncertainty factor of about 30%.
Such inherent uncertainty exposes the more nebulous softness of dredge operations, revealing the inherent lack of certainty of the effects of their own agency, even when rigorously considered. Dredge always entails guesswork and improvisation.
Embedded Intelligence and Self-Organization
The predictive foresight of the Sand Engine is literally and materially external to the operation. The capacity to improvise is enhanced by making dredge itself — sediments in liquid suspension — smart. Imagine embedded intelligence: predictive foresight and sentience integrally distributed within the material of dredge.
Geodetect (another geotextile by TenCate) illustrates the principle. Fiber optic sensors woven into the fabric allow it to read, with exacting sensitivity, soil structure strain and temperature changes in the terrain. (Given the prevalence of geotextiles, that terrain can be virtually anywhere: from roadbeds and railways, to dikes and retaining walls, to tunnels, underground structures and pipelines.)
By reading signals from the intelligent fabric, operators receive early warning of dangerous geotechnical conditions, such as the imminent collapse of karst topography into underground caverns, or the destabilization of a dam. In each case, Geodetect renders dull and inert earth capable of reporting on its own condition, achieving a proto-integration of soil and slope into the Internet of things.
It is easy to imagine a more maximal integration. Picture an EPA erosion tracking program, where tiny particulate sensors are dropped in your backyard. You can watch (in cheerful timelapse) as your topsoil erodes, slides into an adjacent stream and out into the ocean, whence it is dredged to clear a channel before being deposited in a field.
While the original interest in soft systems in the 1970s was highly concerned with user participation, dredge systems are usually characterized by expert control and top-down command structures. (This is no surprise, given that the foremost dredging organization in the US is a branch of the Army.) This structure changes in times of emergency. When soft landscapes perform their predictably unpredicted acts, the management of uncontrolled sediments becomes more spontaneous and open source.
Consider the sandbag — a vernacular technology for emergency response to natural disasters such as floods and infra-natural disasters such as levee failure. They are participatory at both a tactical and strategic scale. One of the enduring images of Midwestern flooding is the chain of volunteers passing sandbags towards the small-town levee The sandbag is small enough, cheap enough, and simple enough that it requires little expertise, and so sandbag emplacements crop up around homes and businesses by the initiation of residents and citizens as often as at the direction of a centralized authority. With a rise in networked dredging technology, we will perhaps see a corresponding rise in self-organizing dredge operations.
The Dredge Cycle
Diagram of the Dredge Cycle. (Dredge Research Collaborative)
Most of these dredge operations and techniques are tangibly applied to single landscapes. They help prevent a neighborhood from being inundated with sediment, or reverse the erosional trend of a coastline. But as the larger and more ambitious techniques we’ve discussed hint, it’s the cumulative interrelationships of these landscapes that really dictates how sediments move and come to rest. It’s the co-mingled gestalt of these altered erosional trajectories that give rise to novel anthropogenic geologies. Systemic softness cannot be reduced to component characteristics, but we can nevertheless identify multiple interlocking trends within it.
The first of these is the transition from a linear process of dredge to the dredge cycle. The dredge cycle is the time-warped anthropogenic sibling to geologic and hydrologic cycles. In some places, it short-circuits or accelerates those natural cycles. In other places it puts massive reservoirs of sediment in suspended animation. Hillsides are liquefied, spilling into the ocean at terrifying speed as physics takes hold of a denuded slope. Winding, shifting rivers are treated like conveyor belts, their courses and depths fixed in place by the industrial renewal of a single moment in time.
As the Dredge Cycle is distributed spatially and temporally in landscapes, inequalities and disequilibriums become clear. Anthropogenic uplift, for instance, operates primarily to cycle sediment at lower elevations — here, closer to the bay — producing a gradual transition of sediment from higher to lower elevations, as geological uplift occurs on far too great a time-scale to counteract anthropogenic erosion.
A Sisyphean Paradox
The landscapes of dredge are fundamentally indeterminate. At the same time, the dredge cycle describes a vicious circle of emergent feedback loops. The processes of dredge, intended to combat erosion and its ill effects, have the unfortunate consequence of themselves producing more erosion and thus more dredge. Through the forces of what might be called anthropogenic erosive entropy — the proliferation of impermeable surfaces, the intensification of storm events due to climate change, the digging of deeper and deeper shipping channels, the loosening of vast tracts of soil for development — ever more material comes under the influence of anthropogenically accelerated erosion. The dredge cycle trends away from being a closed cycle, where sediments are continuously shuffled and recirculated (as water is in the hydrological cycle), and towards being a recombinant spiral of ever-increasing girth.
Indeterminacy and feedback loops together thus cause softness. As we struggle to combat both of these conditions, the process of handling the material gets softer through technological advancements and the proliferation of soft methods. The tools for combating systemic softness, it turns out, are themselves soft, as it is operational softness which best arrests the destabilizing effects of systemic softness.
As human habitation spreads and intensifies, the entire sedimentation and uplift process is becoming ever more anthropogenically constructed and driven. We return to the image of Sisyphus, and of a stability maintained by process. Indeed, the current methods by which humans maintain and shape the landscape intensifies the softness of the landscape itself. Every time Sisyphus climbs the hill, the hill shifts and is remade.
This is where the architectural opportunity lies.
1. Image courtesy of NearMap, 2011 (permission granted under site’s standard free commercial license)
2. Erik Zobrist, 2000, courtesy of NOAA Photo Library.
3. Background Photo: Chris Doley, 1998, courtesy of NOAA Photo Library.
4. Jane Thomas, 2006, courtesy of The University of Maryland Center for Environmental Science, Integration and Application Network Public Image Library.
5. (by Authors)
6. (by Authors)
7. Background Photo: Erik Zobrist, 1998, courtesy of NOAA Photo Library. (Graphics by authors)
8. (by Authors)
Robert E. Randall, “Dredging in the United States”, in Dredging in Coastal Waters, ed. D. Eisma (London: Taylor & Francis, 2006), 157.
Robert E. Randall, “Dredging in the United States”, in Dredging in Coastal Waters, ed. D. Eisma (London: Taylor & Francis, 2006), 148.
Gerard H. van Raalte, “Dredging Techniques; Adaptations to Reduce Environmental Impact”, in Dredging in Coastal Waters, ed. D. Eisma (London: Taylor & Francis, 2006), 1-2.
van Raalte, 5. Uses the term “dredge cycle”, but to refer to a linear process.
Dredging contributes to the acceleration of anthropogenic processes in both large-scale (loose spill layers, poorly structured sediments created in the deposition process) and small-scale ways (release of suspended sediments, overflow, spillage). Van Raalte, 5-7.
In fact, some geologists argue that — in large part because of the way humans have altered sediment transport processes — we are now living in a new geologic epoch, the “Anthropocene”, which is characterized by human impact on sedimentary and geological processes. These geologists note that this human influence constitutes a distinct and noticeable new layer in the geologic record. Elizabeth Kolbert, “Enter the Anthropocene”, National Geographic Magazine, March 2011, http://ngm.nationalgeographic.com/print/2011/03/age–of–man/kolbert–text.
TenCate Geosynthetics, “TenCate Geodetect Solution White Paper”, 2010, http://www.tencate.com/TenCate/Geosynthetics/documents/Geodetect/GeoDetect%20White%20Paper%20Final%202011.pdf.