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OCEAN CURRENT DIVERSION

The land around New Orleans has subsided and the sea level is higher than New Orleans. This situation is getting worse. Henry Stommel, in his book on the Gulf Stream, mentioned that the Gulf of Mexico sea level is 19 cm higher than the sea level on the Atlantic coast of Florida. This gravitational potential appears to me to be the main force responsible for the outflow of the Gulf of Mexico through the Straits of Florida into the shallow passage over the Blake Plateau on the continental shelf. The passage is confined laterally between the Bahama banks and the Florida shore downstream from Miami. The Gulf of Mexico is like a bathtub with a bad drain. We might reduce the danger of flooding New Orleans by reducing the inflow to the Gulf.

This can be accomplished by reducing the surface current through the Caribbean Sea. How would we reduce the Caribbean Current? The Caribbean Sea is separated from the Atlantic Ocean by a ring of islands. The Greater Antilles islands, Cuba, Hispaniola, and Puerto Rico, form the northern end of the ring. The Lesser Antilles form the rest of the ring, which terminates at South America. Water from the North and South Equatorial currents enters the Caribbean Sea via passages between the islands. The Trade Winds from the east are an important source of power driving these currents.

There is not much resistance to the flow through these inter-island passages. However, turbines placed in all the passages could increase this resistance. This would result in more of the Equatorial currents diverting into the Antilles Current, which flows around the Antilles Islands and joins up with the Florida Current north of the Bahamas. There would be little change in the overall circulation of the North Atlantic Subtropical Gyre or the meridional overturning of the Atlantic Ocean.

In addition to reducing the flooding danger of New Orleans, the turbines would reduce the transport of warm surface water through the Caribbean and the Gulf of Mexico. This would reduce the amount of warm water available to intensify hurricanes. The turbines would supply electric power to the island inhabitants, and also power reverse osmosis plants to desalinate sea water for domestic, industrial, and agricultural use. There might be a surplus of fresh water produced in some locations. This can be stored and barged to places where the local production is inadequate.

Turbines in these Antilles passages were proposed by writer Julian Kenny in the Trinidad and Tobago Express on August 28, 2007. He also proposed this in a column in September 2003. He mentions three locations:
1. Columbus Channel, a narrow passage between Trinidad and Venezuela.
2. Galleon's Passage between Trinidad and Tobago.
3. Grenada Passage, a wide, deep passage between the islands of Tobago and Grenada. It is 900 m deep, unlike the first two channels above, which are shallow because they are on the South American continental shelf. The mean transport through the Grenada Passage is 5.4 Sv (5.4 Sverdrups, or 5.4 million cubic meters per second.) The maximum velocity is 60 cm/s at the surface in the center of the channel. A deep core with velocity between 20 and 30 cm/s extends from 250 to 530 m depth and has an average width of 13 km.

There are two other Windward Island passages to the north of Grenada Passage. Listed in order from south to north, they are:
4. St. Vincent Passage between St. Vincent and St. Lucia. 3.0 Sv.
5. St. Lucia Channel between St. Lucia and Martinique. 1.1 Sv.

The Lesser Antilles Islands to the north of Martinique are called the Leeward Islands. The passages in this chain, listed from south to north, are:
6. Martinique Passage between Martinique and Dominica.
7. Dominica Passage between Dominica and Guadeloupe. -0.5 Sv.
8. Guadeloupe Passage between Guadeloupe and Montserrat.
9. Antigua Passage, which I cannot find on my National Geographic map.
10. Anegada Passage in the Virgin Islands. This is a deep passage that allows cold Atlantic deep water into the Venezuela and Colombia Basins.

Going toward the west, there are two passages between the Greater Antilles Islands:
11. Mona Passage between Puerto Rico and Hispaniola.
12. Windward Passage between Hispaniola and Cuba. This is the other deep passage that allows cold Atlantic deep water into the Cayman Trench, the Yucatan Basin, and the Sigsbee Deep in the Gulf of Mexico.

POSSIBLE DEVELOPMENT



Trinidad is a major exporter of liquefied natural gas (LNG) and the U.S. is an important customer. Processing facilities are being expanded and there is a shortage of fresh water. Turbines in the Grenada Passage could supply electric power to operate reverse osmosis desalination plants. The first two passages mentioned by Julian Kenny probably do not have much potential for power generation, but there may be some possibility of local exploitation. The Grenada Passage brings much of the water from the Southern Hemisphere into the Caribbean via the South Equatorial Current that splits on the east coast of South America into the Brazil Current and the North Brazil Current. The North Brazil Current is the return path to the Northern Hemisphere for the meridional overturning water that sinks in the Arctic, flows south at great depth, upwells in the Drake Passage and the Indian Ocean and reaches the South Equatorial Current via the Benguela Current up the west coast of Africa.

Power cables from turbines in the Grenada Passage would probably run to Tobago. What to do from there will require some googling and other investigations of the existing inter-island power transmission facilities and industries (if any) on Tobago. Remembering that the original motivation for this study was to divert currents around the Caribbean in order to reduce the level of the Gulf of Mexico, it will be necessary to examine the needs and resources of the entire Antilles chain in order to design a network of turbines in all of the important passages.

The total transport of the Florida Current is about 30 Sv. Most of it goes through the Gulf of Mexico. Lowering the Gulf sea level by 1 cm would result in a hydrostatic pressure decrease of 0.001 atmosphere or 100 Pa. Multiplying this by 30 Sv gives 3 GW. I think that this means that there would be 3 GW less power to dissipate in friction downstream from the Florida Straits. Perhaps this translates into turbines extracting 3 GW from the currents flowing through the Antilles passages. If this is correct, it means that we might be able to lower the Gulf sea level by 1 cm for every 3 GW we extract from the currents in the Antilles passages, until the relationship gets nonlinear.

Who would pay for this development? Many industries and people in many nations would benefit from the reduced danger of flooding, reduced hurricane activity. and reduction of fossil fuel use. The oil and gas operations in the Gulf would save much money from the reduced interference of the Loop Current with their operations.




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