Dr. Richard LaRosa, sealevelcontrol.com
Of particular concern to Gulf of Mexico operations and the Gulf Coast are hurricanes which gain energy from deep pools of warm water collected by the Loop Current. We can weaken these hurricanes by reducing or eliminating the intrusion of the Loop Current into the Gulf. This article explains how this might be accomplished. Many municipalities, businesses, industries, and individuals of several nations would benefit. A super-agency would have to be established to secure the necessary agreements between nations, distribute the costs equitably, and manage the project.
From observation, study, calculation, consultation, speculation and guessing, I have put together a hypothesis which asserts that the Gulf of Mexico drains into the Atlantic Ocean by gravity, and that the wind-driven hydraulic head at the entrance to the Gulf is almost always greater than what is required to overcome the turbulent-flow resistance of the drain path. The extra head does not increase the volume flow rate because this water comes from long global circulation paths that impose their own limits on the flow. Instead, the Loop Current dissipates the extra power by intruding into the Gulf, sometimes well past New Orleans (as in the case of Katrina in 2005), making a right-hand U-turn, and exiting via the Florida Straits.
My hypothesis is able to explain the observed behavior of the Loop Current. For example, because it is driven by gravity, the Loop Current carves a descending path through the Gulf. The generally higher sea level outside the path provides the hydrostatic pressure required to confine the current to a narrow path, press the legs of the narrow hairpin loop together, and reverse the momentum at the U-turn. When the hydraulic head driving the loop Current decreases, the U-turn cannot retreat against the pressure gradient caused by the steric height of the warm water inside the loop. Instead, the height difference between the go and return legs of the loop facilitates short circuiting the loop and eventually pinching off a ring. The separation sometimes takes months to complete and may involve several cycles of detachment and reattachment. This allows a gradual adjustment to the changing hydraulic head at the Gulf entrance.
Instead of allowing the Loop Current to dissipate the excess hydraulic head, we can use this power to drive turbines installed on buoyant platforms in the Yucatan Channel, Florida Straits, and in the Florida Current channel formed by the Florida coast and the Bahama banks. This can eliminate the Loop Current intrusion into the Gulf.
How great is the surplus head? Leveling surveys were made across the Florida peninsula when there was interest in a canal. Henry Stommel, in his book on the Gulf Stream, mentions a 19 cm difference between the Gulf and Atlantic sea levels. But without knowing the extent of the Loop intrusion at the time of the survey, or the turbulent-flow resistance of each segment of the path, I am forced to make a worst-case guess that the Loop Current segment alone will dissipate 19 cm when it is at its maximum intrusion. For a typically-observed volume transport rate of 25 million cubic meters per second, this maximum Loop dissipates 47.7 GW.
It would be uneconomical to size the system to remove 47.7 GW because we would have excess capacity when the wind-driven head decreases. Suppose we design it to remove 32 GW. This might give acceptable protection. It would limit the maximum intrusion to a third of what it was when Katrina struck. At other times the intrusion would be completely eliminated, and there might be limited periods when the system would not operate at full output.
Assume further that when the system is removing 32 GW, about 16 GW of electric power is produced by the turbines. Most of this reaches the shore grid and the rest is dissipated in electric power losses. The other 16 GW is dissipated in mechanical losses and eddies shed by the mooring cables. If each turbine has an output of 0.25 MW we need 64,000 turbines.
If the water velocity is 1.5 m/s a rotor diameter of 20.2 m is required. The power output is proportional to the cube of the velocity so it is important to place turbines where the velocity is greatest in order to reduce rotor size or use fewer turbines. Turbines must be mounted in pairs rotating in opposite directions to balance the torque. Several pairs can be arranged on a buoyant frame without wake interference.
The foregoing describes a hypothesis and a project based on the hypothesis. The cost of the project should be weighed against the cost of devastation by and recovery from hurricanes energized by passing through warm water pools collected by the Loop Current. The goal is to protect many people and industries from hurricanes in a specific geographic area. We must be sure that people outside this area are not harmed by this project, and we must learn how to share the waterways with the animals that live there. Electric power with no CO2 emissions is a valuable by-product.
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