“If the earth were left alone [without human influence] on the order of eight cubic kilometers (10.5 billion cubic yards) of the material of the continents would be swept away by rivers into the ocean every year…By some estimates, about a third of this natural volume is prevented from reaching the oceans as a result of being trapped behind dams and other [hu]man-made obstructions.” Michael Welland, Sand: The Never Ending Story
[Map of the global distribution of large dams and their reservoirs, overlaid with the percentage of sediment trapped within watersheds by dams. Data supplied by the Global Reservoir and Dam (GRanD) Database.]
There are approximately 800,000 dams* in operation on at least 60 percent of the world’s rivers. Of these dams, 37,641 are registered as “large”, meaning those that are at least fifteen meters in height, or with a minimum reservoir size of three million cubic meters.* Constructed of mass configurations of concrete, steel and earth, their reservoirs have inundated more than 400,000 square kilometers of formerly terrestrial landscape, displacing entire environments and forty to eighty million people within their aqueous footprints.*
A dam’s reservoir acts like a repository for sediments otherwise destined for downstream landforms or the river’s terminus at the sea. As moving water hits these still pools, it decelerates and drops the gravel, sand and silts it was carrying. Most large dams trap and retain 98 percent of their river’s sediment, thus holding a nearly complete material history of the system’s work. Further compounding that load, reservoirs retain additional quantities of sediment caused by increased rates of landscape erosion induced by mining, farming, deforestation and urbanization. Via these surface alterations, the rate at which soil slips from land to sea has exponentially increased. In the United States, ‘geologic’ erosion shears off only about 30 percent of total continental sediment, while ‘accelerated’ soil erosion from human influences accounts for the remaining 70 percent.
Dams are a curious place where the trajectory of accelerated erosion is inverted. Scientists have described dam reservoirs as a “collision space of dispersed and opposing anthropogenic forces” wherein we have “simultaneously increased the sediment transport by global rivers through soil erosion, yet reduced the flux of sediment reaching the world’s coasts because of retention within reservoirs.* A dam creates its own delta, a material congealing of anthropogenic forces. In total, over 100 billion metric tons of sediment and one to three billion metric tons of carbon are estimated to now be inadvertently sequestered in reservoirs mostly constructed within the past 50 years.*
A world inventory of large dams (above) reveals their global distribution to be lumpy, uneven, and politically patterned. Large dam infrastructure typically emerges not only where harvestable rivers are located, but also where pulses of economic incentive and industrial development are occurring. In contrast to nations like India, Brazil and China, the United States is no longer building lots of large dams. The U.S. era of big dam construction took hold around 1940 and reached its peak in the early 1970s.* Today, funding for such projects is not as politically feasible, and more poignantly, most prime locations for dams have already been utilized – a condition know as “site depletion”. Thus the United States is a thoroughly dammed nation, wherein most of its high-flow rivers and opportune canyons are already occupied by strategic barricades of earth and concrete. Consider that the U.S. Army Corp of Engineers currently tracks 84,134 significant dams in its National Inventory. In the U.S., design efforts are more focused on retooling, retrofitting or decommissioning the infrastructure.
In contrast, China currently leads the world in dam construction, both in quantity and size. The nation also has one of the highest rates of continental erosion and is estimated to be losing its soil at a rate fifty-seven times faster than it can be replaced.* At the same time, its super-scaled infrastructures, like Three Gorges Dam, stores approximately 170 million tons of the Yangtze River’s sediment per year, reducing sediments reaching the Yangtze’s coastal delta by as much as 82%, with profound impacts on the morphology of estuary, delta and coastal waters to be expected.* To better situate that agency at a tectonic scale, prior to the dam’s construction the Yangtze river was the world’s fifth largest river of sediment, constituting 4% of all global sediment discharged to the oceans every year.
Taken together, these opposing sedimentary trajectories and collision spaces beg for an interdisciplinary team of designers, political ecologists and speculative hydrogeomorphologists to run scenarios on China’s forthcoming continental structure; a futurism running on radically altered sedimentary budgets, landscape financialization and dam racing; wherein they might encounter peak soil trends merging with a more considered choreography of hydroelectric catch basins.
[Topographic engineering diagram and rendering for the Shuangjiangkou hydroelectric dam. If constructed as planned, the 44 cubic meter earthen dam will be 314 meters tall with a total reservoir storage of 2,897 million cubic meters]
Seen as an aggregate collection of hydro-geological megaforms, dam infrastructure is a tectonic body of sorts, with its own migration patterns and reservoir-induced earthquakes. Perhaps this dispersed geographic network of monumental slabs of concrete, stilled water, turbines, and masses of sediment is a provisional example of a hyperobject. As conceived by Timothy Morton, hyperobjects are things like global warming and plutonium 239 that defy local circumscription and bounded temporality. Like dams and their decelerated rivers, they are “massively distributed in space-time.”* They are viscous, squishy, and uncanny things we cannot escape, outlive or distance ourselves from. The extremity of our co-intervention in the circulation of water and sediment seems matched by the extremity of the notion that our agency can be fully removed from them.