Titanic Seawall Construction with Minimal Resources -- A Public-Domain Invention
One of the great uncertainties of climate change (aka global warming) is how fast the land-based polar icecaps will melt and consequently raise sea levels. One thing we do know is that with even modest increases in ocean levels, most of our coastal cities and towns will be gravely threatened. If you had a simple, inexpensive method for building massive seawalls, with an implausibly minimal expenditure of energy and raw materials, you would at least have an optional method for protecting major cities, or even minor towns.
On the other hand, there are existing demands for megascale seawall projects today. The city of New Orleans might well rest easier if her citizens could quickly and cheaply raise up a wall facing the sea capable of withstanding the mightiest hurricanes, the people of the Netherlands might also feel better if they could further reinforce their nation’s already formidable levy system, and there are those individuals who would simply like to wall off a small estuary as part of a tidal-power project.
While any of these options (and particularly the last one) should be weighed carefully from an environmental perspective, I have decided to include the following invention because any of these applications could prove necessary to people facing a dire emergency. Whether protecting newly flooded lands, reinforcing existing flood defenses or seeking a new, vast source of renewable power, societies may find themselves in need of this technique.
The core invention behind this process, incidentally, is not mine, and has in fact apparently been in public domain for some time. But I have added two potentially key modifications to the process to increase its utility for megascale projects. The system itself – if the original inventor’s observations and calculations are correct – should prove incredibly useful in the right circumstances, even without including my ideas in its operation.
"Sea-ment" is a cement-like material formed when you apply an electric current to a metal grid in seawater. Mineral ions dissolved in seawater (such as calcium carbonate) bond electrochemically to the charged metal, forming a kind of cement coating. Calcium carbonate is extremely common in surface waters, and is a positive ion in seawater. If a positively charged anode and a negatively charged cathode are suspended in seawater with a current flowing between them, ions of calcium and carbonate will combine and accumulate on the cathode. These ions and other minerals will continue to build up as long as the current flows.
Typically you use a sheet of metal mesh, supported by conductive reinforcing bars, to serve as the cathode. These wires will become steadily more encrusted as your current flows through them. The gaps in the mesh eventually fill, creating a solid slab of what is essentially reinforced concrete. By putting sheets of this mesh within ½ inch of each other, you can create slabs of sea-ment of any thickness you choose.
The stronger the current, the faster this material accumulates, but ironically, the weaker the sea-ment that will result. The concrete used in sidewalks has a strength of 3,500 psi (pounds per square inch). Ordinary sea-ment created on ½ inch hardware cloth is about 20% stronger. The strongest form of sea-ment is created by very slight flows of current and is accumulated over long periods of a year or more – resulting in strengths of up to 8,000 psi.
According to sea-ment’s inventor, Wolf Hilbertz, at a current density of 189 mA/ft2, a tenth of an inch of sea cement will accrete on ½ inch wire mesh in 170 hours. At this pace, .0005 inches/hour, the space in ½ inch mesh will be completely filled in after 500 hours, or about three weeks. At 12 volts, a kilowatt of power can generate a current density of 189 milliamps per square foot over an area of 441 square feet. In theory, then, 400 or so megawatts of electricity devoted to this work could produce several million tons of sea-ment over the course of a year. Clearly a tremendous investment of energy, though not so much when you consider the raw energy (and material) costs of creating several million tons of slightly less durable conventional concrete and then shipping it to a seashore for construction. But where would you get that kind of power?
Well, leaving aside other inventions for now – and we may have something far more powerful and sustainable to share with the world in the not-too-distant future – you can always manage generate a substantial fraction of the above power using a tidal barrage system. Such systems typically effect turbidity, salinity, sediment movements and kill some fish in their turbines. But they also generate a great deal of power. (Of the three operating, the largest on the Rance River can generate up to 240 megawatts at peak production.)
The principle behind tidal barrages is quite simple. Essentially, the tide is allowed to flow through sluices into a walled-off stretch of seashore. Then the sluices are closed, and the water flows out through the system’s turbines. Quite a bit of energy can be thus generated every time the tide recedes, particularly if you have a large (and therefore more ecologically disturbing) project, and, of course, the working turbines to tap all that power.
Again, given the environmental concerns, tidal barrage systems are not to be undertaken lightly, if at all. (I prefer environmental impacts of effectively zero, myself.) But if you are confident enough in the measures you have taken to compensate for these problems, or certain enough that the coastal environment can not be effected by them (because you have, for example, already turned it into a barren waste incapable of supporting any sea life), or – let’s be blunt – you’re already desperate enough due to an energy collapse or global-warming meltdown that these potential problems fade in importance compared to the ecological and/or human devastation sweeping in your direction... well, then here is a simple blueprint for how to create this system rather cheaply.
It’s assumed most organizations undertaking the construction of a megascale seawall backed by tidal-barrage electricity have limited resources in terms of energy, assuming they are not facing some kind of global disaster (like rapidly rising sea levels). After all, if you had a great excess of energy, you would not need the tidal barrage system in the first place. In that case, start small and build your way up – walling off a very small estuary, cove or what-have-you to begin with (using sea-ment, of course), and use the energy created by the ebb and flow of that particular tide to create the sea-ment-based seawall for the next, larger stage of your project – another, even larger tidal barrage.
Eventually, you will have enough local power to handle whatever level of seawall construction you need... and if you’ve been clever, your tidal barrage seawalls can probably be included into whatever set of city or general coastal defenses you are working on.
Finally, part of the point of your megascale structures may be to protect you not only from existing sea levels, but from the risk of an extremely rapid rise brought on by a sudden glacier slide-off or an unprecedented storm surge associated with a major hurricane. How can you use sea-ment to counter such problems without falling back on the crude solution of producing slabs of the material underwater and then setting those sections on top of the primary sea-ment seawall you have already created beneath the waves? That plan may work if you have a crane and many workers, but ideally you would prefer a single powerful structure more or less grown together, not a set of slabs bolted together atop an impressive, well-integrated foundation.
Once again we turn to my hydraulic water pump system, in this case the tidal hydraulic pump, for assistance. By setting up a robust system (as described earlier in this series) that takes in a considerable amount of water and kinetic force from the incoming tide, you can then direct a portion of that water to rise to the top of your wall, spilling carbonate-saturated seawater over your structure with every movement of the ocean. A gentle but near-continuous flow of seawater should give your electrical mesh the raw materials it needs, especially if you can shape your piping and layer your mesh to slow down and break up that flow as it descends, increasing the amount of time that water spends in contact with your cathode. At worst, you should at least be able to create a partially accreted mass of seament to serve as a framework if the structure is abruptly drowned or if you have to add something manually to that above-surface mass.
I have not seen other assessments of Wolf Hilbertz’ figures for this slow-paced, low-energy accumulation of sea-ment, and would suggest experimenting on a very small scale to see how well his method works in your waters, regardless. If, for example, you have no environment to threaten with tidal barrages because tremendous acidification of your seawaters have killed off all native life... well, a further downside may be the impact of high acid levels on your sea-ment and wire meshes. Hopefully, most builders will not be in that position, but a small amount of inexpensive testing seems a wise precaution, regardless.
(Oh, and regarding the above innovation -- yes, it is a toy compared to my windpower system for free mega-scale desalination and water pumping (and extremely low-cost electrical generation), and yes, if the tidal-redirection concept doesn't work out, you'll have to move water by a more conventional (but still very simple) means, such as a reciprocating pump attached to a piece of your tidal barrage that generates no electricity, just kinetic energy. (At early stages of the project, the tide alone will be a more than adequate water source, and you will only need pumps of whatever description if you intend to build a truly towering structure.)
Oh, and if you're interested in the free mega-scale desalination system, and its associated renewable-electrical generation, feel free to contact me, if you are a government, non-profit power co-op or charity with relevant activities. Unlimited supplies of free water by reverse-osmosis desalination (it's the kinetic power that pumps that water that is free to those using the system) would do a great deal to handle global-warming-driven drought, and I have absolutely no desire to charge anyone for water.)