Sverdrups & Brine

A “Sverdrup,” named after the famed Norwegian geologist who defined this unit of measure, is the largest quantity commonly used to express volumes of water flow. Naturally, the highest volumes of water flowing on this planet are ocean currents, such as the Gulf Stream, which warms Europe and flows at a rate of of 30 to 150 Sverdrups, depending on latitude.

So how much water is in a Sverdrup, after all? Apparently, one Sverdrup is equivalent to “one million cubic meters of water per second.” In practical terms this is equivalent to delivering one cubic kilometer of water (weighing exactly one gigaton) in just under seventeen minutes. That is one heck of a lot of water. That is a very big pipeline.

And what do Sverdrups have to do with brine? It has to do with whether or not to approve construction of desalination plants, which if built using modern technology all over the world, would eliminate world water scarcity. Apparently environmentalist conventional wisdom says it’s ok to install marine current turbines and offshore windmills and tidal hydro installations, but one cannot lay a pipeline capable of transporting tens of cubic kilometers per year of brine into an ocean current, because it will make the ocean saltier. But this objection completely overlooks the volume of offshore marine currents, expressed in Sverdrups.

Brine comes from desalination plants. “Brine” is a painfully misleading word, since normally a desalination plant returns seven parts of slightly saltier water, referred to as brine, to the ocean for each unit of fresh water that is extracted from the seawater. At less than 20% saltier than the ocean, it doesn’t take much current to easily disburse this volume of brine.

A cubic kilometer (km3) of fresh water can easily sustain 3.0 million people in residential urban and suburban settings, since one cubic kilometer is sufficient to provide 241 gallons per day per person to a million people – 913 liters per day per person! This would work in places such as greater Los Angeles, since with seven km3 of brine for every km3 of recovered fresh water, desalinating water for sixty million residents would only require 140 km3 per year of water to get dumped into the California channel. Wow! 140 cubic kilometers of brine discharge per year! 34 cubic miles! That’s a lot of seawater, 16% saltier, going into any ocean, isn’t it?

No. Just one Sverdrup of current volume is equal to 31,558 cubic kilometers per year. This means in a one Sverdrup current the brine discharge pipes from desalination plants servicing 60 million people would disburse brine that, per year, would increase the salinity of the current by a mere seven one-hundredths of one percent. And in the California current which is at least several Sverdrups even fairly close to shore, the impact of brine from 60 million people’s water desalination would probably be at most a tenth of that, or seven one-thousandths of one percent, especially when one considers the subsurface to surface upwellings, different currents, which also move Sverdrup volumes of water per year off the coast of California.

As for power requirements, a cubic kilometer of fresh water can be extracted from the sea for less energy than it takes to pump this water over the Tehachapi Mountains. So if you like wave and current and tidal energy, break out the underwater bulldozers and while you’re at it, desalinate water for Southern California, and turn off the pumps.

One Response to “Sverdrups & Brine”
  1. Brian Hayes says:

    In July 2007, the public utility branch of the Singapore government reported the world’s lowest cost to desalinate part of its water supply at US53 cents per cubic meter. They’ve replaced the conventional 8 inch process pipe with a new 16 inch reverse osmosis system. Singapore imports more than half it’s water under expiring contracts from Malaysia and is looking toward water independence.

    Does this new cost factor reflect your impressive challenge? I call it “The Tehachapi Calculation”!!


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