When dealing with a drought or a bushfire, is a million tons of water overkill?

Question

The people of the Vorfall Panzer Werkstat gesellschaft build the largest aircraft in the galaxy. The pride of their fleet is currently the Gyre Explorer, which is an aircraft weighing in at 140,000 metric tons,capable of carrying 70,000 metric tons of cargo, covered with armour equivalent to the citadel armour of a WWII battleship, and capable of a constant 4g acceleration with its reactionless drives. It is used for exploration and trade.

However, VPW Gt is contemplating an even bigger aircraft, a water tanker/bomber capable of scooping, transporting and dumping a million tons of water... yes, a whole gigaliter of water, capable of accelerating at 1.5g to 2g at full load with its atomic power plants and reactionless drives.

Like any VPW aircraft, it would be capable of operating in the vacuum of space for at least a month. Its maximum atmospheric speed would be limited by the capability of its hull to withstand heating at high speeds in an atmosphere rather than the power of its drives.

This aircraft is intended to be used to collect, transport and deliver water for drought relief and fighting large scale bushfires.

My question is this: Would a gigaliter of water delivered by an aircraft capable of supersonic flight be sufficient capacity to deal decisively with large scale droughts and bushfires by the standards of modern-day Earth, or is it overkill?

Edit:

Water could be collected by lowering the VTOL aircraft into a suitable body of water and opening the valves, and delivered by opening the valves at any suitable altitude. The valves are capable of variable flow, but the full load could be collected or dumped within ten minutes or less, at a rate of up to 2.5 megaliters per second in a 1g environment.

Lower flow rates and broad dispersal are possible by partially opening valves and increasing altitude.

Edit 2

I was never proposing having this aircraft just quickly dump a gigalitre of water in one shot in order to deal with a drought or fire. A fire might be dealt with by dropping water from a high altitude at a rate just sufficient to extinguish the fire but not the trees. To deal with a drought, water might be shipped to reservoirs, not just dumped on farmland.

Answer 1

dosis sola facit venenum applies also to this case, I think.

There is so much water that soil can absorb in a given span of time, anything more than that will simply flow, and with flow comes erosion.

Now, 2.5 million liters of water dumped on a streak few hundred meters long would scourge it from soil, plants, houses and whatever else stand in its path. It would be a delivered tsunami. It's like treating a pimple with an angular grinder.

Just take a look at what happened with the Vajont Dam:

The impact displaced 115 million m3 (4,100 million cu ft) of water in approximately 25 seconds, 50 million cubic metres (1,800×106 cu ft) of which overtopped the dam in a 1⁄4-kilometre high (250 m; 820 ft) wave.

The impact with the water generated three waves. One went upwards, reached the houses of Casso, fell back onto the landslide and went to dig the basin of the pond of Massalezza. Another headed toward the shores of the lake and, through a washout action of the same, destroyed some localities in the municipality of Erto e Casso. The third (containing about 50 million cubic metres (1,800×106 cu ft) of water) climbed over the edge of the dam, which remained intact except for the ring road that led to the left side of the Vajont, and fell into the narrow valley below.

The approximately 50 million cubic metres (1,800×106 cu ft) of water that managed to climb over the work reached the stony shore of the Piave valley and swept up substantial debris, which poured into the southern sector of Longarone and destroyed the town except for the town hall, the houses north of it and other neighboring towns. The death toll was about 2,000 people (official data speaks of 1,917 victims, but it is not possible to determine with certainty the number).

While somebody suggested that to stop forest fires we should get rid of all the trees, it doesn't sound like a wise advice.

Nor I can imagine any farmer being happy seeing their farm and soil being washed away in a pile of mud to help them overcome a drought.

Answer 2

A gigaliter is 1 million cubic meters. So that much water will cover a square kilometer of land to a one-meter depth.

Dumping that much of water in ten minutes would be less "firefighting" and more "dam failure" in terms of the volume and flow rate. You wouldn't be putting out the brushfire so much as scouring it back down to bedrock. Communities downhill from your drop zone would no longer have to worry about losing their homes to the fire, since they would instead have been swept away by a flash flood wave several meters high.

So, yes, that would be overkill.

With that much tank capacity, you'd want a muuuuuch slower dispersal rate. The goal wouldn't be to bomb a single area as hard and fast as possible as much as it would be to provide enough water to as large an area as possible. Especially if your purpose is drought relief, you'd want to do many fine-dispersal passes over a large area--basically simulating rainfall--rather than just dumping it all in one spot.

Answer 3

A drought means a reasonably large area getting not enough rain. Suppose this area were 100 km x 100 km, a modest agricultural zone. This is 10,000 square km. This is something in the range of 1/10th the farm land in Minnesota.

Minnesota typically gets between 700 mm to 1000 mm of rain per year. Suppose you only need to provide 500 mm to provide for growing corn and such.

You need 0.5 m x 10,000 square km, or 5E9 cubic meters of water.

Your ship carries 1E6 cubic meters, since 1 m$^3$ of water is pretty close to one metric ton. So you need to make 5000 trips per year, predominantly in the growing season. So in-the-range-of a trip every half hour for 3 months or so. Out and back, plus filling time and drop time. If you have to go to Lake Michigan to get the water, it adds to the distance. So you are very likely to need to go supersonic to do it.

For drought relief it's tiny. And the sonic booms on the round trips are going to be seriously annoying. You are going to burn a lot of fuel doing that, even with reactionless thrusters. Probably easier, cheaper, and less annoying, to use some kind of canal system.

Note that 1 km$^3$ is 1E9 m$^3$, so you need about 5 km$^3$. Lake Michigan contains about 4,900 km$^3$, so you are probably OK on that score.

Answer 4

Oh yeah, it's overkill

I live in a small town of about 2,000 people. Our town council announced that for the 2021 year the pumps that fill our town's water tank pumped just over one million gallons of water. How much does one million gallons of water weigh?

4,170 tons

Now, granted, what we have is a small town of people, some of whom are watering gardens, others are watering lawns... this comparison is not at all against subsistence living. Honestly, this consumption could be considered closer to the lap of luxury. Still... it's a Real World example. So, how long would one million tons of water last?

239.8 years

Another way of looking at this is, what size town could you sustain for a year with this mother hubbard of an airplane?

479,616 people

Assuming infinite fuel and given the acceleration of the proposed plane, you could keep an entire nation supplied with water pretty much indefinitely. Your real problem is the time required to move that volume of water onto and off of the plane. But I can think of a couple of ways to deal with that (the Los Angeles County storm drain system, famous for water and Hollywood space shuttle landings, comes to mind).

Answer 5

A million tons of water is roughly 767 acre-feet, i.e. enough water to cover 787 acres with one foot of water, assuming fresh water with a weight of roughly 8 pounds per gallon.

You'd be hard-pressed to put that much into a spacecraft of just about any kind, at least in a single trip, as the largest aircraft carrier is roughly 4.5 acres in size. You'd need an absolutely monstrous vehicle to hold 767 acre-feet and huge amounts of delta-v if you're trying to go between worlds.

As far as whether it can relieve a drought, well, that depends on how much of an area and how many people. 767 acre-feet is enough for a small reservoir to water a town, it could certainly water a large farmland, but it probably wouldn't water more than a few tens of thousands of people.

For comparison, Beaverdam reservoir in Northern Virginia is approximately 300 acres. It has a smaller surface area than your million tons of water, but because it has an average depth of around 15 feet, it actually holds around 4500 acrefeet of water, more than 5 million tons or so.

The Beaverdam reservoir is designed to be one source of water for Fairfax county, which has a population of 1.1 million.

Using the USA's average per-capita water use of 3800 liters per day (which is actually fairly middle of the road compared to other nations), Beaverdam reservoir could provide enough water for all of Fairfax county's residents for about 1 year.

So, your million tons of water could sustain a population of 1 million people for about 2.4 months, assuming zero recycling, which would be unusual. The water doesn't just "magically disappear" after it's used, and could be treated and reused over and over so long as you have the energy to do so.

As far as bushfire control, the amount of water needed is much smaller. However, water is almost never used by itself, but is mixed instead with a fire-retardant of some kind. Bushfires aren't just doused into submission; what actually happens is that they are controlled by laying fire breaks and fire retardant in such a way that the fire's extent is limited and it burns itself out.

In that case, a million tons of water is probably enough for most common brushfires, but a large scale fire might overwhelm what's available.

Answer 6

I think you ought to do a more thorough research on Wildfire containment. I say "containment" because I even want to avoid the word "suppress". From what I've seen on the news and from this source, water availability itself is not the main problem and nowadays we already have means to deal with wildfires using local water sources. Even in the far future, local sourcing will most likely remain the most efficient choice. In addition, a wildfire has multiple "faces" and is affected by many variables of terrain and weather, such that efforts to fight it are concentrated in pockets where the fire is growing, or ahead of the fire (in strategies that eliminate fuel or dig trenches). If any aircraft is to disperse the water, it will probably be a swarm of lighter craft that can attack several spots at once and maneuver rapidly to respond to changing conditions.

All this points to a massive spaceship not being needed for either the transportation of water or its deployment.

As for fighting drought, at first glance it should be useful to fill up reservoirs in critical condition. But, then again, looking at the capacity of reservoirs near my city, they have around hundreds of millions to billion liters of capacity (sorry, the source is in Portuguese). The ship wouldn't even come close to putting a dent on the water demand in a couple of trips. You would need an entire armada to keep the necessary flow of water to replenish a reservoir. Not to mention that it's probably one of the most expensive options, even in the far future. It would be more efficient to pump water from nearby sources than to fly it. Another far cheaper technology is desalination.

The only way I see this ship being useful in water transportation is in ship to ship transactions (or station to station) out in interplanetary space.

Answer 7

For fighting forest fires a 1 million ton water carrier is MASSIVELY over kill.

The link indicates that fighting three major forest fires required 765,090 gallons of water, which is just under 2,900 cubic meters. That is, one load of your water carrier is 345 times the size required for three major fires. You could do that every day for nearly a year with one load.

By the way, the link indicates that the retardant is not all that useful. Plain old water is quite good at fighting fires. They use it because it looks good.

Answer 8

Not a whole answer, but a concern suggesting overkill.

Where is the water being sourced?

Many of the lakes and rivers that are in arid regions are unlikely to tolerate more then a few loads extracted before consequences are too severe to allow more water extracted. Which will mean longer trips to locations with more water.

Sourcing water is an issue with currently existing water bombers. Higher volumes make this worse. To the point where it may be needed to move water internationally which has lots of political problems.