All weather extremes caused mainly by Climate change
Venice meanwhile is sinking
mb-soft.com/public2/venice.htmlKeeping Venice from Sinking into the SeaSimilarly, Raising New Orleans to be back above Sea Level
The cities of Venice, Italy and New Orleans, Louisiana have a tremendous problem in common, they are build on river sediments and are slowly sinking into the sea. Venice (the old city) is currently virtually exactly at sea level (and sinking) while New Orleans is already around 6 feet BELOW sea level (and sinking) and has had to be protected by levees surrounding it which keep the Mississippi River and a large lake and the water from the Gulf of Mexico out. The concept described here suggests a possible way that either or both cities might be actually physically raised up (at the rate of around an inch per month), such that either or both cities might eventually be high enough not to have to have survival concerns regarding being inundated by water. In the case of Venice, by the year 2050, the old (historic) portion of Venice will be permanently lost under the Adriatic Sea. In the case of New Orleans, the city's future really depends on how well all the hundred miles of levees can withstand hurricanes and terrorist bombings.
During the mid-Twentieth Century, the city of Venice, Italy had sunk unusually rapidly as a result of many wells pumping out large amounts of water that had been hydrostatically contributing to support the entire region. The process is reversible! By now pumping substantial quantities of river water DOWN those wells, that hydrostatic support can be now replaced, which would act to raise the entire region gradually over months and years. VERY large amounts of water are required, and Venice has several available rivers to provide it.
This approach depends on three conditions:
Water is essentially incompressible;
Venice is build on layers of sediment and sedimentary rock;
Some of those layers are permeable to water, and at least one is impermeable.
The first is certainly true, and the other two must be true if any water wells have ever pumped water out of them, and they have. The very last condition, of the existence of an impermeable (clay) layer is nearly always true when sediments have been deposited for many thousands of years.
In November 2002, the American PBS science program NOVA aired a program on "Sinking City of Venice". The program reminded us that the city of Venice, Italy has been slowly sinking for at least the last several centuries. The level of much of the city has now gotten to the point of being critical. If nothing is done, the city will certainly be totally destroyed by tides and storm waves within a few decades. The fact that global warming has also begun to melt the polar ice caps, which causes the sea level to also be rising, compounds the problems of their sinking city.
The city leaders have gotten to the point of being desperate for a solution. In recent years, they have begun pursuing an incredibly expensive and unusual project to try to preserve their city. The concept involves the installation of enormous movable steel "gates" under the waters of their lagoon. The idea is that, when high tides are coming in, these gates would be raised to block off the Mediterranean from their lagoon, much like the concept of the doors of a lock of a canal.
Their application is very different from that of a lock, and massive engineering has been proceeding for some time. By the time they expect to be able to start installing their gates, which they hopefully expect in around ten years, they will spend at least two to three billion euros.
That approach has very serious potential problems, in addition to the enormous price tag. It still involves the city continuing to sink and the sea level rising due to global warming. Even if they pay for and install those gates, and even if they work as the promoters claim they will, few people expect them to have useful effect beyond two or three decades. At that point, Venice's problems will be even more severe, assuming it still exists, because it will be virtually entirely below the average sea level.
It is a sign of how desperate the city leaders are to be seriously pursuing this extremely expensive and unproven technology. They are extremely aware that the very existence of their city is at risk.
An Alternative Approach
I believe that there is a FAR more logical course to pursue! One that can be initiated within weeks instead of ten years, and which would cost thousands rather than billions of euros. It also does not involve the assortment of environmental problems that the gates approach is likely to cause, and actually has no environmental impact at all! In addition, it actually RAISES the entire city, ensuring the continuing existence of Venice for centuries to come!
During the NOVA program, there was a brief mention of a situation that occurred in the middle of the 20th century. From around the 1930s to the 1970s, factories in the nearby Port Marghera drilled a number of wells and pumped substantial amounts of groundwater up and out from underneath the city, for their various industrial processes. Much of that used water then ran off out into the Mediterranean Sea. The city leaders were soon horrified to find that their city had begun sinking much faster than ever before. When they suspected a relationship with the wells, they were ordered closed, and the sinking soon slowed to its normal rate. During that period, the city of Venice dropped around 9" or 22 cm.
Water is essentially incompressible, and by removing a given volume of water, that much volume of underlying supporting material no longer exists under the city. For many locations, that might just leave air-filled caves or smaller chambers between the solid particles of material. But Venice is built on sedimentary materials which tend to slowly flow to fill in such voids, as a response to gravity. That is the reason why pumping water out caused an increase in the rate of the land sinking.
THIS I believe is the secret to solving Venice's dilemma!
The technical name for the process where the land is sinking is called subsidence. During approximately that same time period, farmers in the San Joachim Valley in California pumped enormous amounts of water for irrigation. While that water had been deep in the sedimentary layers, it had acted to hydrostatically support the overlying layers. Once it had been pumped out, the land level subsided. In the case of that California Valley, so much water had been removed that the surface level dropped by around 10 meters vertically!
My suggestion is that I believe that it is possible to cause "reverse subsidence"! I believe that Venice should immediately reactivate those industrial wells, and potentially drill more wells. However, instead of drawing water FROM the wells, I propose to pump water, under standard pump pressure, INTO the wells.
The two important facts are that (1) water is incompressible; and (2) all sedimentary soils and rocks necessarily have pore spaces between the grains of the materials. It does not matter that weight has compressed the materials, the pore spaces between the grains of the material cannot be completely removed. Yes, those pore spaces under Venice are smaller than they used to be, which is why the city has sunk. But the majority of those pore spaces cannot be made to completely disappear, except by an extreme situation of metamorphosis into rock, which can only occur deeper than around 8,000 meters deep.
Any Geologist knows that around 40% of the volume of nearly any sediment is actually these pore spaces. One of the earliest things a Geophysics student learns is that a container filled with spherical ball bearings has about that much pore volume. If any sedimentary material replaces the ball bearings, the proportion of pore space remains about the same, 40% void space. The particle-to-particle contact actually supports the upper layers, but the pore spaces do not disappear! Imagine a kitchen glass filled with spherical marbles. There is a lot of space between the marbles that cannot be eliminated. If an underground layer was only 10 meters thick, and somehow ALL the pore spaces were eliminated, the land surface would have dropped by around 4 meters! The fact that the actual drop in recent centuries is less than 1/10 of that establishes that around 90% of the volume of the pore spaces are still present. They represent paths for water to again easily flow. That is essentially why water wells can work in the first place!
The specific nature of the sediment affects how rapid and easy this flow might be. A layer of sand has very large pore spaces, so water can flow very easily and rapidly. If the layer is the much finer clay materials, the pore spaces still exist and still allow water flow, but the smaller pore spaces represent smaller pathways for the water to seep through. This has the effect of allowing slower seepage flow for clay layers as compared to sand layers. When the well was first drilled, the driller must certainly have drilled it to a depth where a permeable layer was present. Otherwise, the well would not have worked in the first place. That essentially ensures that all existing wells could be "reversed".
By pumping water down into the (existing) wells, it will flow into those existing pore spaces. Since the water is incompressible, it must then necessarily take up space (volume). By adding this volume of water into those pore spaces, the particles might be slightly pushed apart, and the combined volume of soil, sediments, sedimentary rock and water is therefore increased. This necessarily requires that the land surface must rise as a direct consequence.
This is actually basic Physics, and anyone familiar with Physics can confirm this logic.
It might first seem that extremely powerful pumps would be needed. That is not the case. If the water was allowed to just flow down the wells (unpumped) the pressure in that water would rise as it went deeper. For every 10 meters in depth, it rises naturally by around 700 Pa (15 PSI). Therefore, even water that just drained into wells would arrive at the bottom at a pressure that was essentially the same as that existing in nearby areas. The (standard) water pumps would be necessary to give that water a slight additional local pressure (say 3 kPa (50 PSI), if that was the rating of the pump) such that it would quickly seep outward (due to that differential pressure) through the sedimentary materials down there. Again, if the layer was a clay layer, possibly a stronger pump might be needed, but no well driller would have first drilled the well into such an impermeable layer. Therefore, standard (economical) water pumps could certainly be used.
There are several nearby rivers that should provide adequate supplies of freshwater. Examination of the quantities of water removed during the mid-20th century should give a guideline to the quantity of water that would represent each inch of altitude for the overlying layers, and the city itself.
Let's say, for argument's sake that the entire 500 square kilometers of the land and lagoon area would be involved deep underground. Simple calculations show that 2.5 cm (1") thick of water for that huge area would be the equivalent to about 13 million cubic meters of water. Therefore, if the wells collectively pumped, say, 20 million cubic meters of water down the wells (which provides for a substantial amount of natural horizontal outward seepage), and since water is not compressible, there would be little alternative to the entire land surface rising around 2.5 cm (1") in altitude!
Even a modest sized industrial pump can pump 400 liters (about 100 gallons) per minute, or 600 cubic meters per day, down into a well. One thousand such pumps would therefore pump around 600,000 cubic meters of water down into the underground aquifer each day. In a month, that is around the desired 20 million cubic meters of water. Therefore, in just a single month, it should be very practical to raise the entire 500 square kilometer lagoon region by 2.5 cm or one inch, each month.
Additional wells and pumps, or using larger pumps, could make the effect even more rapid. Also, if the affected area happens to be less than the full 500 square kilometers we have been considering, the local rise of the land could be substantially quicker.
However, even with just this moderate effort, in one year, the entire region could be raised by around 30 cm (one foot). At whatever point when the city leaders felt the land was high enough, pumping could be slowed, to just provide for that lateral seepage, to maintain that altitude. It seems certain that even a rise of three to five feet in altitude should be reasonable.
Rather than spending several billion euros on the gates project, which may or may not work for a few decades, and which could only begin to have any productive effect ten years from now, I strongly recommend that Venice immediately attach pumps to all the existing wells and start pumping river water down into the wells. If the gates project was still to proceed, both approaches could be pursued simultaneously. Many of those pumps may already exist and only need to be reversed. Since a number of wells were already drilled, and they may still have pumps attached, there would be virtually zero expense involved in beginning this approach. Access to river or sea water would obviously be necessary, so some surface piping might be necessary, but the total cost is extremely low.
At the very most, a few thousand euros expense would be involved in reversing the plumbing on a single existing well pump, to confirm that large amounts of water can be pumped down the well. Even with such a limited experiment, modern instrumentation is so advanced as to be able to measure very small fractions of an inch rise in the surface immediately around the well.
The nearby industrial companies may even be willing to absorb the expense of doing that to wells adjacent to their factories, in order to get positive press coverage of attempting to help save Venice. In that case, the total cost to the city would be exactly zero for many of the wells!
Rather than having to wait for at least ten years before any productive effect might occur, cessation of the current sinking would occur almost immediately and reversal of it soon afterwards (for that immediate area). That would confirm the validity of this approach, in an extremely low-cost, immediate experiment.
All the experts agree that even a single inch in altitude has tremendous importance for Venice, and this proposal could certainly raise the entire city by an inch within the first month!
Again, if it was considered truly urgent to raise the city farther and faster, to better preserve the brickwork that is dissolving in the seawater, then larger pumps and additional wells could certainly be added. It does not seem to be out of the question to raise the entire region by several feet within one year, should that be desired. However, such a rapid raising might tend to be initially somewhat localized. Depending on the permeability of the sub-surface layers being affected, water flow horizontally outward from a well takes some amount of time. If extremely large quantities of water were quickly injected into a specific well, a local "bulge" would be likely to occur in the land surface in that immediate area, which would gradually spread outward. If a very rapid rise-rate was desired, injection wells would need to be drilled in a relatively uniform pattern, such that the entire region was raised at the same rate. Otherwise, differential stresses might be caused in buildings which could cause potential cracks to form in them.
At the suggested one-inch-per-month surface rise rate, this effect of differential rising would be unmeasurable, the buildings would be fine, and existing wells should perform excellently.
There are NO environmental difficulties associated with this approach! Pumping freshwater down into aquifers and subsurface sedimentary layers occurs naturally anyway, but very slowly. No bad environmental effects would occur as a result of this approach. The easy access and convenience of Adriatic seawater might encourage consideration of injecting seawater instead. Such an effort would add several complications. Pumps and piping tend to corrode faster when exposed to saltwater, and pump maintenance costs would certainly be higher. Future use of that subsurface permeable layer as a well source would be eliminated as it would have saltwater in it. Also, salt accumulations would certainly occur within the pore spaces of the permeable layer, which would likely gradually restrict the ability of water to spread outward from the well in the permeable layer.
There is also no downside to doing water injection. This activity would not affect or eliminate any other approaches that might otherwise be considered. Even if the effects would be considered less than desired (which could only occur if too large an amount of the pumped water was able to seep out without productive effect) no other alternatives would be affected. However, even if a large amount of seepage was found to occur, it is certain to be possible to pump even more water in and possibly under higher pump pressure, to always be able to accomplish the desired effect.
I am a caring person, a Physicist, in America, who is concerned about the well being of the people of Venice and the architectural and art treasures. I am not trying to get hired, or to receive any consultation fees. Actually, I believe that I have described what needs to be done very completely right here! No other significant Engineering or design work really needs to be done to begin! After a month or a year of pumping known amounts of water down the wells, the relationship should quickly become clear between the quantity of water and the amount of vertical rise, which figures to be pretty uniform over the entire region that would be filled underground. This presentation is my personal gift to the people of Venice. It is certain to work, it is very economical, and it can be begun immediately.
This same approach is likely to have similar beneficial effects for any city that is over sedimentary materials, such as perhaps, New Orleans, Louisiana, in the United States. New Orleans is a city that has subsided so much as to currently be around six feet BELOW sea level! For over a century, New Orleans has had to be surrounded by over a hundred miles of levees, earthen walls intended to keep out the (higher) River, Lake, and Gulf water. As global warming continues to melt the polar ice caps and sea levels are rising, such cities are in peril. In the case of New Orleans, being already so far beneath sea level, it is especially prone to the levees being compromised by either a major hurricane or a terrorist attack.
This approach can allow the entire city (and region) to be physically raised to a slightly higher altitude, in order to always be above sea level.
Updated News
In June 2002, I sent an e-mail to the Mayor of New Orleans, offering to oversee the installation of appropriate injector wells, at no charge, where I would have only received ANY payment based on actual measured raising of the ground in the area. The Mayor never answered my note and neither did anyone else. I also contacted a Professor who has long been known as warning about flooding disasters for New Orleans. He didn't answer my e-mail either!
Hurricane Katrina
In September 2005, Hurricane Katrina missed directly hitting New Orleans, but the storm was so strong that it still caused water to overwhelm the levees and the city of New Orleans was seriously flooded. Now that that has happened, and so seriously, there is probably little point in now trying my approach there. If New Orleans is to be rebuilt, it probably only makes sense if enough dirt and landfill is brought in to raise the entire city by around 10 feet vertically, so it would be a few feet above sea level. Even then, the city is still sinking, and within a few more decades, it would again be at or below sea level. A serious problem, which has no satisfactory solution.
