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I don't think the article mentions this but this is directly related to the drought in Panama. Apparently they had a huge lake reservoir for storing freshwater

I don't think the article mentions this but this is directly related to the drought in Panama. Apparently they had a huge lake reservoir for storing freshwater that was then used to fill the locks in the canal. And then subsequently release into the ocean. They haven't gotten the usual rainfall and this is causing serious issues. > https://www.cnbc.com/2023/11/03/panama-canal-drought-hits-new-crisis-level-amid-severe-el-nino.html https://www.cnbc.com/2023/11/03/panama-canal-drought-hits-ne...

TrapLord_Rhodo 3y ago
How does this make any sense? Why would you need freshwater to go through a canal that connects two bodies of water? This seems like very poor planning and infrastructure creation. why can't they pump sea water through the locks?
- ViewTrick1002 3y ago
  Why pump millions of tons of sea water when the rain does it for free? Where will you store the sea water without poisoning the lake? The new locks have added mechanisms to decrease water loss, but they do require water.
- mlyle 3y ago
  Because that's a whole lot of seawater to pump. Each ship has to be lifted 85 feet in several stages, and the ships are big. Not to mention that there are lakes in the interior part of the canal.
- yjftsjthsd-h 3y ago
  Speculation: You probably don't need it, but it could be a lot easier if the lake has some elevation (so you don't need to spend so much energy pumping), and being freshwater means less corrosion to contend with. And whatever the reasons, it was probably built like that way back when and retrofitting it now is, again, possible but hard/expensive.
  - carl_dr 3y ago
    The freshwater is because the lakes in the centre of the canal are freshwater, and you don’t want to kill the ecosystem in and around them.
- guerrilla 3y ago
  Elevation.
- michaelbuckbee 3y ago
  I was curious so I did a quick bit of googling and apparently portions of the canal are actually lakes (Gatun and Miraflores Lakes). Here is a cross-section diagram of the canal showing the lakes: https://www.marineinsight.com/wp-content/uploads/2018/09/panama-canal-1024x727.jpg https://www.marineinsight.com/wp-content/uploads/2018/09/pan...
- swashboon 3y ago
  It connects 3 - 4 main bodies of water, the lakes in the middle are a high spot compared to the oceans on either side.
  - SoftTalker 3y ago
    In the absence of the canal, did these lakes naturally drain to the sea, or are they in some sort of natural "bowl" that is higher than sea level?
    - marcosdumay 3y ago
      Very few lakes on the planted don't drain to the sea. They are usually salty, smelly water bodies that nobody wants to be around.
    - kzrdude 3y ago
      See the cross section https://kids.britannica.com/students/assembly/view/68621 https://kids.britannica.com/students/assembly/view/68621 "Natural bowl higher than sea level" could be called a lake.
- fencepost 3y ago
  They could likely retrofit to do so but there'd be a lot of ecological concerns along with the infrastructure and energy cost of pumping billions of gallons of water from sea level. Ecological concerns wouldn't just be pumping seawater into a large freshwater lake but questions of where to intake water, cross contact between the Atlantic and Pacific oceans there at a new location, etc. Not a trivial set of issues.
- FriedPickles 3y ago
  I enjoyed this well made video illustrating how it works: https://www.youtube.com/watch?v=jh79YSCC8mM https://www.youtube.com/watch?v=jh79YSCC8mM And this one explaining how reservoirs can be used to trade-off water consumption for land requirements using side ponds: https://www.youtube.com/watch?v=SBvclVcesEE https://www.youtube.com/watch?v=SBvclVcesEE
- deleted 3y ago
  [deleted]
- reliablereason 3y ago
  It would require about 14 MWh to lift a single ship to the upper level Calculating the approximate wattage to lift all that water 26m: 9.8 w/s * 200000000 Liters * 26 m /60/60/1000/1000 200 000 000 liters was reported on wikipedia as amount of water used. Its a very crude calculation probably of by quite a bit. It's allot of electricity but the cost of that electricity would be essentially nothing when compared to what they charge. So I don't know why they don't install massive pumps. Maybe they don't want to contaminate the lake with salt water, but you would get small amounts of salt water with the current system to.
  - celdon25 3y ago
    > So I don't know why they do what they do. Supply and demand?
    - marcosdumay 3y ago
      At $200/MWh, that would be around $3k by ship. The energy cost is almost irrelevant on the current supply/demand equilibrium.
  - cellis 3y ago
    Can you break this down for the mere mortal physics minds here? How did you do this calculation??
    - Faaak 3y ago
      Simple E=mgh. m = mass of displaced water h = height of displaced mass g = gravity
    - kurthr 3y ago
      I did it myself, it's about 10MW continuous assuming there are 40 ships each taking about 3000 seconds to traverse the locks. Each lock is ~30x330x10 cubic meters or 1Billion liters (conservatively). A Watt is 1 meter(lift) x 1 Newton / second. There are 30 meters of lift. Each liter is 1kg and gravity (9.8m/sec2) makes that about ~10 Newtons (9.8N due to gravity). So you get 10^9kg x 10N/kg x 30m / 3000 sec = 100MW continuous. That's about 100, 000 horsepower. Each lock would need more than 16MW of pumping. Solar/hydro power from the rain in lake Gatun is well over 100MW. Due to leakage it's probably 5-10x that or equivalent to a larger nuclear power plant.
- kurthr 3y ago
  Because the locks were built where they were over 100 years ago without the need for any pumps since there was an existing lake. The number of pumps, installation time, and power needed to run the locks (in both directions since the middle is at the top) would be huge. I could still happen, but take a decade to build out. The vertical rise is about 26meters and there are 3 10meter locks (33mx300m in size) in each direction. 40 ships travel through each day (~3ksec per fill bidirectional) and each fill is ~1Billion liters or 250Million gallons in less than an hour. Lifting 1B liters through 30m would need 100MW to power 100% efficient pumps continuously for leakless locks. The solar/hydro power of rain is significant. Also, everything in the lake would die once it was contaminated with sea water, and you would be contaminating the Pacific with Atlantic water, vice versa, or both.
  - perihelions 3y ago
    Would it be practical to integrate pumped hydroelectric energy storage into a canal lock mechanism? Pump water up to lower the water level; harness water flowing back down for electricity; and arrange the timing partly towards grid supply & demand. Maybe dig a third reservoir adjacent to the lock mechanism, as a buffer between the two levels, to give you more flexibility with the timings. [late edit]: Apparently this is in fact a thing, in some cases: - "The hydraulic cylinders enable the water used by the locks to be pumped back. Up to 48,000 cubic metres of water are displaced in a single lockage operation. In periods of low discharge on the Meuse, the screws can pump back the water lost due to the passage of a ship through the lock to the upper canal reach. In normal periods of enough discharge at the Meuse, the screws are used to to generate green electricity from hydropower." https://www.inlandnavigation.eu/power-of-water-and-wind/ https://www.inlandnavigation.eu/power-of-water-and-wind/
    - jacquesm 3y ago
      > harness water flowing back down for electricity; Too little head for good efficiency.
  - kylehotchkiss 3y ago
    > you would be contaminating the Pacific with Atlantic water Ahh that's what must be making the Drake Passage so angry.
- speed_spread 3y ago
  It's much easier to use direct hydraulic power from inland upstream fresh water bodies. That's how most locks work, you just let gravity do the work. This is super basic technology that can still reliably move up million ton cargo ships.
- Ekaros 3y ago
  Because those connecting fresh water bodies are higher than the sea. So the cheap solution is to fill progressively higher boxes with water from the fresh water, until you are at fresh water. And then do same thing in reverse. Perfectly fine when you have enough fresh water, you can even somewhat optimize by using same water multiple times. But if you run out of fresh water at high point you will have trouble.
- patmorgan23 3y ago
  Because it goes ocean -> canal -> massive fresh water lake/river system -> canal -> ocean. Just Google a video of a ship passing through the Panama canel
iav 3y ago
The locks are filled with recycled water that is stored in water saving ponds [1], but this only reuses 60% of the water and it doesn't address the other issue that if the water level in the natural lakes in Panama interior is too low, then ships will have a harder time navigating between the locks. [1] <https://maritime-executive.com/article/panama-canal-first-water-saving-basin-filled https://maritime-executive.com/article/panama-canal-first-wa...>
- gwright 3y ago
  I believe that is just the newer sets of locks. The older set doesn't have that recycling mechanism.
- pietjepuk88 3y ago
  The thing that complicates the use of the water saving basins, is that they tend to make the salt intrusion into the lake a lot worse [0]. So to limit the salt intrusion (through the new locks), they have to _not_ use the water saving basins, or flush the locks every now and then using a lot of fresh water from Gatun lake. This was (and is) not as much an issue with the old locks, as passage of ships there is ridiculously fast with the use of mules. With the new locks, it's mostly tug boats, and substantially bigger/slower ships obviously. [0] Mostly on the Agua Clara side. The Cocoli side is generally fine, as the salt wedge doesn't reach the lake. Drinking/irrigation water intakes there probably have to be (or have been) moved though.
whyenot 3y ago
It's also a little more complicated than that. A lot of the water for the canal comes from Lake Alajuela, which was formed by damming the Chagres River. Because of deforestation and rapid erosion, the lake has been filling with silt and is no longer able to hold as much water as it used to. This is a problem that has been known for the last few decades, but very little has been done to address it. This current problem is especially bad because the dry season normally begins 4-6 weeks from now and there will be little rainfall to re-fill Lake Alajuela (or the lake its water flows into, Gatun Lake, the backbone of the canal). (I previously worked for the Smithsonian Tropical Research Institute in Panama and lived on an island in the Panama Canal)
- dieselgate 3y ago
  Cool thanks for some perspective on things. Didn't know the Panama Canal is big enough to contain residential islands.
  - nickstinemates 3y ago
    It's huge. I recommend visiting it, and, zip-lining across the lakes. It's a sight.
  - trelliscoded 3y ago
    The canals are just the edges of the entire path, the part in between is enormous compared to them. Because they flooded a forest, there’s a lot going on in the intermediate lake.
- killjoywashere 3y ago
  Comments like above are why I keep coming to HN. Dam it!
- j1elo 3y ago
  > Because of deforestation and rapid erosion, the lake has been filling with silt and is no longer able to hold as much water as it used to. This is a problem that has been known for the last few decades, but very little has been done to address it. So that lake is like the small open source project that supports the weight of all internet: critical for everybody, yet neglected. The Canal moves such amounts of money every year, not to say over decades, that preserving the lake in better conditions ought to have been easy. Now the ball of mud is exploding in their faces. It's like if "we" (collectively) never learned.
dessimus 3y ago
Certainly the additional set of parallel locks opened in recent years would only serve to hasten the speed with which they are dumping the fresh water into the oceans on each side.
- happytiger 3y ago
  Nobody ever mentions this part.
- dylan604 3y ago
  Seems to me that if you forced the locks to be used in sync so that as the water was being lowered in the exiting lane, its water was being used to raise the ships in the entering lane. This is such an absurdly simple idea, that there must be a reason it is not happening. Does anyone know what the water isn't shared between the 2 lanes at each level? Is it something with different mass between the ships means the amount of water is not always equal?
  - AnimalMuppet 3y ago
    The water from the "down" ship can be used to raise the "up" ship... until it's at the same level as the down ship. Then you're stuck [Edit: unless you have] either water coming from the elevation of the top of the locks, or pumps.
    - closewith 3y ago
      Not in the Panama Canal as traffic is one way.
      - ayewo 3y ago
        Do you have a source for this claim that traffic is one-way? This article from 2003 talked about two-way traffic on the canal: https://pancanal.com/en/panama-canal-begins-tests-of-simultaneous-two-way-transits-at-canals-most-narrow-channel/ https://pancanal.com/en/panama-canal-begins-tests-of-simulta...
  - 3y ago
happytiger 3y ago
The fifth paragraph: > A queue of ships waiting to use the canal has been growing in recent months amid a deep drought. To manage the situation, the canal’s managing authority has announced increasingly drastic restrictions for the depleted thoroughfare. The Panama Canal Authority also holds auctions for those wishing to jump to the front of the line. It’s in there. :)
iambateman 3y ago
It’s wild that world shipping depends in some small part on the rainfall in Panama.
- deleted 3y ago
  [deleted]
- nomel 3y ago
  I suspect there's an SEP [1] running at at least 12V in the vicinity, most likely blocking a rather large spacecraft, that's been stationed stationed near the canal, possibly before it was built! It's the only logical explanation. 1. https://hitchhikers.fandom.com/wiki/Somebody_Else%27s_Problem_Field#:~:text=A%20Somebody%20Else%27s%20Problem%20field,field https://hitchhikers.fandom.com/wiki/Somebody_Else%27s_Proble....
paulcole 3y ago
the article in fact mentions drought in the 5th paragraph.
HomeDeLaPot 3y ago
Good article. Says they're already using some solutions that have been raised in these comments, like recovering (some of) the water used and moving some cargo by rail (to meet weight limits).

TrapLord_Rhodo 3y ago

How does this make any sense? Why would you need freshwater to go through a canal that connects two bodies of water? This seems like very poor planning and infrastructure creation. why can't they pump sea water through the locks?

ViewTrick1002 3y ago
Why pump millions of tons of sea water when the rain does it for free? Where will you store the sea water without poisoning the lake? The new locks have added mechanisms to decrease water loss, but they do require water.
mlyle 3y ago
Because that's a whole lot of seawater to pump. Each ship has to be lifted 85 feet in several stages, and the ships are big. Not to mention that there are lakes in the interior part of the canal.
yjftsjthsd-h 3y ago
Speculation: You probably don't need it, but it could be a lot easier if the lake has some elevation (so you don't need to spend so much energy pumping), and being freshwater means less corrosion to contend with. And whatever the reasons, it was probably built like that way back when and retrofitting it now is, again, possible but hard/expensive.
- carl_dr 3y ago
  The freshwater is because the lakes in the centre of the canal are freshwater, and you don’t want to kill the ecosystem in and around them.
guerrilla 3y ago
Elevation.
michaelbuckbee 3y ago
I was curious so I did a quick bit of googling and apparently portions of the canal are actually lakes (Gatun and Miraflores Lakes). Here is a cross-section diagram of the canal showing the lakes: https://www.marineinsight.com/wp-content/uploads/2018/09/panama-canal-1024x727.jpg https://www.marineinsight.com/wp-content/uploads/2018/09/pan...
swashboon 3y ago
It connects 3 - 4 main bodies of water, the lakes in the middle are a high spot compared to the oceans on either side.
- SoftTalker 3y ago
  In the absence of the canal, did these lakes naturally drain to the sea, or are they in some sort of natural "bowl" that is higher than sea level?
  - marcosdumay 3y ago
    Very few lakes on the planted don't drain to the sea. They are usually salty, smelly water bodies that nobody wants to be around.
  - kzrdude 3y ago
    See the cross section https://kids.britannica.com/students/assembly/view/68621 https://kids.britannica.com/students/assembly/view/68621 "Natural bowl higher than sea level" could be called a lake.
fencepost 3y ago
They could likely retrofit to do so but there'd be a lot of ecological concerns along with the infrastructure and energy cost of pumping billions of gallons of water from sea level. Ecological concerns wouldn't just be pumping seawater into a large freshwater lake but questions of where to intake water, cross contact between the Atlantic and Pacific oceans there at a new location, etc. Not a trivial set of issues.
FriedPickles 3y ago
I enjoyed this well made video illustrating how it works: https://www.youtube.com/watch?v=jh79YSCC8mM https://www.youtube.com/watch?v=jh79YSCC8mM And this one explaining how reservoirs can be used to trade-off water consumption for land requirements using side ponds: https://www.youtube.com/watch?v=SBvclVcesEE https://www.youtube.com/watch?v=SBvclVcesEE
deleted 3y ago
[deleted]
reliablereason 3y ago
It would require about 14 MWh to lift a single ship to the upper level Calculating the approximate wattage to lift all that water 26m: 9.8 w/s * 200000000 Liters * 26 m /60/60/1000/1000 200 000 000 liters was reported on wikipedia as amount of water used. Its a very crude calculation probably of by quite a bit. It's allot of electricity but the cost of that electricity would be essentially nothing when compared to what they charge. So I don't know why they don't install massive pumps. Maybe they don't want to contaminate the lake with salt water, but you would get small amounts of salt water with the current system to.
- celdon25 3y ago
  > So I don't know why they do what they do. Supply and demand?
  - marcosdumay 3y ago
    At $200/MWh, that would be around $3k by ship. The energy cost is almost irrelevant on the current supply/demand equilibrium.
- cellis 3y ago
  Can you break this down for the mere mortal physics minds here? How did you do this calculation??
  - Faaak 3y ago
    Simple E=mgh. m = mass of displaced water h = height of displaced mass g = gravity
  - kurthr 3y ago
    I did it myself, it's about 10MW continuous assuming there are 40 ships each taking about 3000 seconds to traverse the locks. Each lock is ~30x330x10 cubic meters or 1Billion liters (conservatively). A Watt is 1 meter(lift) x 1 Newton / second. There are 30 meters of lift. Each liter is 1kg and gravity (9.8m/sec2) makes that about ~10 Newtons (9.8N due to gravity). So you get 10^9kg x 10N/kg x 30m / 3000 sec = 100MW continuous. That's about 100, 000 horsepower. Each lock would need more than 16MW of pumping. Solar/hydro power from the rain in lake Gatun is well over 100MW. Due to leakage it's probably 5-10x that or equivalent to a larger nuclear power plant.
kurthr 3y ago
Because the locks were built where they were over 100 years ago without the need for any pumps since there was an existing lake. The number of pumps, installation time, and power needed to run the locks (in both directions since the middle is at the top) would be huge. I could still happen, but take a decade to build out. The vertical rise is about 26meters and there are 3 10meter locks (33mx300m in size) in each direction. 40 ships travel through each day (~3ksec per fill bidirectional) and each fill is ~1Billion liters or 250Million gallons in less than an hour. Lifting 1B liters through 30m would need 100MW to power 100% efficient pumps continuously for leakless locks. The solar/hydro power of rain is significant. Also, everything in the lake would die once it was contaminated with sea water, and you would be contaminating the Pacific with Atlantic water, vice versa, or both.
- perihelions 3y ago
  Would it be practical to integrate pumped hydroelectric energy storage into a canal lock mechanism? Pump water up to lower the water level; harness water flowing back down for electricity; and arrange the timing partly towards grid supply & demand. Maybe dig a third reservoir adjacent to the lock mechanism, as a buffer between the two levels, to give you more flexibility with the timings. [late edit]: Apparently this is in fact a thing, in some cases: - "The hydraulic cylinders enable the water used by the locks to be pumped back. Up to 48,000 cubic metres of water are displaced in a single lockage operation. In periods of low discharge on the Meuse, the screws can pump back the water lost due to the passage of a ship through the lock to the upper canal reach. In normal periods of enough discharge at the Meuse, the screws are used to to generate green electricity from hydropower." https://www.inlandnavigation.eu/power-of-water-and-wind/ https://www.inlandnavigation.eu/power-of-water-and-wind/
  - jacquesm 3y ago
    > harness water flowing back down for electricity; Too little head for good efficiency.
- kylehotchkiss 3y ago
  > you would be contaminating the Pacific with Atlantic water Ahh that's what must be making the Drake Passage so angry.
speed_spread 3y ago
It's much easier to use direct hydraulic power from inland upstream fresh water bodies. That's how most locks work, you just let gravity do the work. This is super basic technology that can still reliably move up million ton cargo ships.
Ekaros 3y ago
Because those connecting fresh water bodies are higher than the sea. So the cheap solution is to fill progressively higher boxes with water from the fresh water, until you are at fresh water. And then do same thing in reverse. Perfectly fine when you have enough fresh water, you can even somewhat optimize by using same water multiple times. But if you run out of fresh water at high point you will have trouble.
patmorgan23 3y ago
Because it goes ocean -> canal -> massive fresh water lake/river system -> canal -> ocean. Just Google a video of a ship passing through the Panama canel

iav 3y ago

The locks are filled with recycled water that is stored in water saving ponds [1], but this only reuses 60% of the water and it doesn't address the other issue that if the water level in the natural lakes in Panama interior is too low, then ships will have a harder time navigating between the locks. [1] <https://maritime-executive.com/article/panama-canal-first-water-saving-basin-filled https://maritime-executive.com/article/panama-canal-first-wa...>

gwright 3y ago
I believe that is just the newer sets of locks. The older set doesn't have that recycling mechanism.
pietjepuk88 3y ago
The thing that complicates the use of the water saving basins, is that they tend to make the salt intrusion into the lake a lot worse [0]. So to limit the salt intrusion (through the new locks), they have to _not_ use the water saving basins, or flush the locks every now and then using a lot of fresh water from Gatun lake. This was (and is) not as much an issue with the old locks, as passage of ships there is ridiculously fast with the use of mules. With the new locks, it's mostly tug boats, and substantially bigger/slower ships obviously. [0] Mostly on the Agua Clara side. The Cocoli side is generally fine, as the salt wedge doesn't reach the lake. Drinking/irrigation water intakes there probably have to be (or have been) moved though.

whyenot 3y ago

It's also a little more complicated than that. A lot of the water for the canal comes from Lake Alajuela, which was formed by damming the Chagres River. Because of deforestation and rapid erosion, the lake has been filling with silt and is no longer able to hold as much water as it used to. This is a problem that has been known for the last few decades, but very little has been done to address it. This current problem is especially bad because the dry season normally begins 4-6 weeks from now and there will be little rainfall to re-fill Lake Alajuela (or the lake its water flows into, Gatun Lake, the backbone of the canal). (I previously worked for the Smithsonian Tropical Research Institute in Panama and lived on an island in the Panama Canal)

dieselgate 3y ago
Cool thanks for some perspective on things. Didn't know the Panama Canal is big enough to contain residential islands.
- nickstinemates 3y ago
  It's huge. I recommend visiting it, and, zip-lining across the lakes. It's a sight.
- trelliscoded 3y ago
  The canals are just the edges of the entire path, the part in between is enormous compared to them. Because they flooded a forest, there’s a lot going on in the intermediate lake.
killjoywashere 3y ago
Comments like above are why I keep coming to HN. Dam it!
j1elo 3y ago
> Because of deforestation and rapid erosion, the lake has been filling with silt and is no longer able to hold as much water as it used to. This is a problem that has been known for the last few decades, but very little has been done to address it. So that lake is like the small open source project that supports the weight of all internet: critical for everybody, yet neglected. The Canal moves such amounts of money every year, not to say over decades, that preserving the lake in better conditions ought to have been easy. Now the ball of mud is exploding in their faces. It's like if "we" (collectively) never learned.

dessimus 3y ago

Certainly the additional set of parallel locks opened in recent years would only serve to hasten the speed with which they are dumping the fresh water into the oceans on each side.

happytiger 3y ago
Nobody ever mentions this part.
dylan604 3y ago
Seems to me that if you forced the locks to be used in sync so that as the water was being lowered in the exiting lane, its water was being used to raise the ships in the entering lane. This is such an absurdly simple idea, that there must be a reason it is not happening. Does anyone know what the water isn't shared between the 2 lanes at each level? Is it something with different mass between the ships means the amount of water is not always equal?
- AnimalMuppet 3y ago
  The water from the "down" ship can be used to raise the "up" ship... until it's at the same level as the down ship. Then you're stuck [Edit: unless you have] either water coming from the elevation of the top of the locks, or pumps.
  - closewith 3y ago
    Not in the Panama Canal as traffic is one way.
    - ayewo 3y ago
      Do you have a source for this claim that traffic is one-way? This article from 2003 talked about two-way traffic on the canal: https://pancanal.com/en/panama-canal-begins-tests-of-simultaneous-two-way-transits-at-canals-most-narrow-channel/ https://pancanal.com/en/panama-canal-begins-tests-of-simulta...
- 3y ago

happytiger 3y ago

The fifth paragraph: > A queue of ships waiting to use the canal has been growing in recent months amid a deep drought. To manage the situation, the canal’s managing authority has announced increasingly drastic restrictions for the depleted thoroughfare. The Panama Canal Authority also holds auctions for those wishing to jump to the front of the line. It’s in there. :)

iambateman 3y ago

It’s wild that world shipping depends in some small part on the rainfall in Panama.

deleted 3y ago
[deleted]
nomel 3y ago
I suspect there's an SEP [1] running at at least 12V in the vicinity, most likely blocking a rather large spacecraft, that's been stationed stationed near the canal, possibly before it was built! It's the only logical explanation. 1. https://hitchhikers.fandom.com/wiki/Somebody_Else%27s_Problem_Field#:~:text=A%20Somebody%20Else%27s%20Problem%20field,field https://hitchhikers.fandom.com/wiki/Somebody_Else%27s_Proble....

paulcole 3y ago

the article in fact mentions drought in the 5th paragraph.

HomeDeLaPot 3y ago

Good article. Says they're already using some solutions that have been raised in these comments, like recovering (some of) the water used and moving some cargo by rail (to meet weight limits).