By the time it gets to "flood" most of them will die before they get 10 miles out of the city. Thirst, hunger, and misadventure will claim most of them. Especially when they're on day two of three without water and start thinking "hey! RIVERS ARE FULL OF WATER!!" yet have no idea what "filtration" is.
What you're describing is the "Golden Horde Theory." We have debunked it several times.
Indeed. What I see is the "Killer Caravans" by Kurt Saxon. I copied the whole thing for posterity, but keep in mind, his "I would dos..." are not only at this point and time illegal, but are also dangerous and likely to get you killed as well.
THE KILLER CARAVANS by Kurt Saxon copyright 1979
When the collapse comes, whether from a total economic
breakdown or nuclear war, surviving city dwellers will scatter like
their cockroaches when they turn on their kitchen lights. Millions
not killed by the war, the fires, the rioting and the street
battles, will take to the countrysides.
The roads leading out of the doomed cities will be hopelessly
clogged with wrecked vehicles, looking like any foggy morning on
the San Francisco freeways. As many city vermin as will be trapped
in the jams, scads of that rubbish will make it to the main
arteries from the cities to the smaller towns.
These will be the "lucky". The provident will have left before
the chaos. But the lucky will get out by sheer luck, with little or
no gear, no extra gas, probably a gun or two, a box of canned goods
and a few bottles of booze they looted. But not meaningful survival
gear.
Until they get to the nearest town, it will be dog-eat-dog.
Every man for himself and let the devil take the hindmost. If they
stop for an overturned car ahead, it will just be to search the
passengers for any useful items and to siphon out any gas left in
the car.
Finally, dozens of individual vehicles will reach the nearest
town. In most cases, the townsmen will have the roads barricaded.
They could not hope to accomodate hordes of improvident city types,
so will, all too often, just block their way and turn them back at
gunpoint.
This method is wrong and I'll explain why in my next
editorial, "Roadblock". But at this time, I want to tell you what
will happen as a result of total roadblocking, which will be common
around most American towns.
You can easily imagine such roadblocks, made of cars strung
across the road, bristling with guns held by determined townsmen.
Signs reading, "Go Back or Get Shot!" or "Yankee Go Home!", and
suchlike, will let the refugees grouping at the roadblocks know
they are unwelcome.
Although, up to then, these refugees will have been
individuals, they will now form into mobs. Being improvident and
having no chance on their own, instant leaders will spring up
before the roadblocks and offer the mobs their protection and
guidance.
In times of catastrophe and confusion, the average person is
too often willing to follow anyone who says he has an answer.
Anyone with any sort of previous authority, or who will do the
thinking for those unable to think, will find a ready-made army to
go wherever he leads and do whatever he orders.
"Lucifer's Hammer" by Larry Niven and Jerry Pournelle,
describes two such leaders and many of their sub-leaders, all
relativelyy unqualified in times of order. But when the comet came
close to Earth, the most unlikely leadership was accepted, and like
Jim Jones of Guyana, brought savagery and death to all their
followers.
The two main leaders in "Lucifer's Hammer" were a black Army
Sergeant and a white religious fanatic. It was an interracial
group, made up mostly of a band of soldiers, black activists and
white losers picked up on the line of march.
Food was scarce so cannibalism became, not only acceptable,
but mandatory. The eating of human flesh was part of the initiation
into the band. If one would not eat, he was eaten.
This was first ordered by the Sergeant, as an immediate
alternative to starvation. It was later made a commandment by the
religious co-leader, as a sign of faith in the idea that they were
God's chosen. Only the chosen would be blessed with victory over
the surviving technologists who had brought God's wrath on a sinful
world. And God would forgive their cannibalism and any other
horrors committed while bringing His Kingdom into fruition.
His degenerate ravings are pretty much mirrored on TV by Billy
Graham, Rex Humbard, Pat Robertson and Anal Roberts. The kind of
people who swallow everything these perverts say, ended up
swallowing human flesh, just as eagerly. So, like swarms of
locusts, these cannibalistic fanatics proceed to ravage and destroy
the only hope for a future civilization.
There will indeed be such leaders as Sergeant Hooker and the
messianic Reverend Henry Armitage. There will also be bands made up
of cults living inside or outside of cities. These cults will move
out first and do what they will with the uninitiated or those who
will not convert.
But the most common bands will be groups turned back from
roadblocks. These, as well as the rest, will form Killer Caravans,
pooling their resources. The leader, whether a politician, soldier
or self-acknowledged messiah, will have a ready-made, media
brain-washed band of killers to do his bidding.
His first act will be to kill off the uncooperative and anyone
who can't see him as the rightful head. At first, the loudest will
be followed. If this loudest doesn't keep the majority on his side,
his position and/or his life will be in jeopardy.
Of course, if the loudest proves really incompetent another
might kill him without fear of the majority. Also, the loudest
might appoint a deputy or two, both to keep the malcontents in line
and to keep one of the deputies from taking his place.
So with the leadership established, the malcontents killed off
and their property confiscated by the group, the Killer Caravan is
formed. It has its leaders, either military or charismatic, or
both. It has its armed foragers and looters. It has its compliment
of women and children as dependents.
But what it lacks is a direction, a place to go, a purpose.
All it has as a social organism made up of improvident
establishment hacks, urban workers and welfare loafers, is the
collective will to survive.
With resources pooled and the unwilling either dead or driven
off, the Killer Caravan forms up. It then moves back down the road
to any promising side road giving access to a route around the
restricted town.
The side road they choose might pass your home. With too
little food to last, and nothing to lose, they will most certainly
move against you. The Killer Caravan might number from 20 to 100 or
more people.
Regardless of how much or how little you had stored away, the
Killer Caravan would strip you of everything. Nor would they feel a
need to spare your life. After commandeering your vehicles,
weapons, total food supply, they would hardly expect you to feel
anything but hatred for them. Giving in to them would be no
guarantee that they'd let you and your family live.
First, they'd camp on your place until there was nothing left.
There'd be no sense in believing they'd actually settle in on your
property and share it with you and help you work it. They wouldn't
be farmers, anyhow and since you'd have only one or two cash crops
and a subsistence garden, such a mob would have no reason to take
over your holdings on a long-term basis.
No, they'd camp on your place for a day or two and gather up
everything you had that they wanted. After a short time, there
would not be enough to feed the band and they'd move on to the next
farm, probably leaving you dead.
These are the kind of people the boondockers must prepare
against. You should set up a communications network with your
neighbors with walkie talkies. Chances are, the Killer Caravans
would attack only one farm along their route at a time. This would
give your neighbors a chance to meet at the first farm on their
route so as to meet them in force.
Fighting Killer Caravans would be different from defending
against lone refugees and their families. In the case of loners,
you might be generous, set out food enough for them to get to the
next area, and with a moderate show of force, save yourself from
all-out attack.
But with Killer Caravans, you must show deadly force at once
and keep it up until the survivors are discouraged into moving on.
First, they will have no alternative to attacking you, as they will
face chronic shortages which will halt their caravan without
replenishment. Second, their morale will depend on victories. With
the low morale of the members, the leaders might just as well pass
out the poison.
Regardless of the numbers in a caravan, there is little
likelihood that it would be made up of professionally trained
ex-servicemen. Even so, if you can impede them, and inflict a high
enough casualty rate, they will move on, even if they have to do so
on foot.
The common conception of a Killer Caravan is of a
well-organized, well-equipped, well-armed, disciplined unit. It is
said that such caravans would sweep all before them. "Lucifer's
Hammer" paints a picture of an almost overwhelming horde.
If such a group would take a few farms and stay put, they
could start their own survival community. But the Killer Caravan
would not have the quality of personnel to become a successful
survival group. They would be vulnerable, relying mainly on the
disunity and incompetence of farmers along their route.
I would have a ball eliminating a Killer Caravan. I would
plant mines at the entrance to my farm. The POOR MAN'S JAMES BOND
shows how to set them off electronically without wires. Of course,
I would not have them armed, or even implanted until the collapse
had actually occurred. But then I would implant and arm and when a
caravan vehicle entered the gate into my property; pow!, there'd be
a flaming wreck blocking the entrance.
I would also implant such mines behind trees, fences,
outbuildings, etc.; wherever a caravaner might shoot from. Then
blam, boom, splat; I'd have caravaners filling the air.
If I were stuck with a wooden house I'd install sprinklers
along the roof. And under the eaves, I'd string garden hose with
holes in it so the outside of the house would be drenched, in
anticipation of firebombs. Of course, I'd have a gas generator to
operate the well pump.
I'd cover my windows with chicken wire and open them all up;
again in anticipation of firebombs and also bullets. (No need to
get all the windows shot out.) This would be done if I had not had
time to install metal shutters with rifle ports.
In each room would be a chair with a pillow or rolled blanket
tied to the top of its back for a rifle rest. Each chair would be
slightly back from the window, seat forward, as I wouldn't want the
raiders to see any guns pointing out.
I'd rely on my 30-06 bolt action Remington 700 with the proper
scope for the distance from the house to the road and nearest
hiding places. Upon seeing the raider, I'd kneel behind a chair,
cushion the rifle on its back and shoot him in the right shoulder,
if possible. (Anyone with the minimum of practice can hit a six by
six inch target at 200 yards, almost every shot.)
You might think a clean kill would be better, but not when
you're dealing with a Killer Caravan. A body is just one less mouth
to feed. But a man with his main shoulder shot would be a useless
drain on the food and medical supplies.
Also, in the heat of an action, the others would be far less
apt to identify with a corpse than a mate screaming at them for
help. Further, a few such injuries would cause the women to bitch
and urge them to move on. Another thing about wounding a raider is
that with the scarcity of medical supplies, his suffering and
probable death would give his fellows a lot of food for thought. If
it occurred to them that the object was to wound and maim, any
number of them would be apt to vote to move on.
If, instead of moving on, they attacked in force, I'd shotgun
them. Mine holds 11 shots and shoots as fast as I can pump it.
Single ought Buck at 12 30 caliber pellets each round are quite
effective at 100 yards. Hardly aiming, I can get three pellets in a
one foot circle at that distance. That's the same as being shot
with nine .30 caliber Carbine rounds. Really sets a man down.
I would never shoot a woman or a child, unless they were
shooting at me. Dead wives and kids enrage the husbands and make
them just as intent on revenge as on taking the position.
With dogs on the place to let me know if the attack took place
at night, I would use a new tactic. I'd have already booby trapped
the entrance with a mine and so would flee upwind from the caravan,
carrying an electronic detonator. While they were making their
plans, I'd open a half-dozen one-pound containers of sodium or
potassium cyanide and place them strategically around the caravan
so the wind would blow the gas their way. (See the PMJB for making
cyanides.)
Then I'd pour in hydrochloric acid, going from one to the
other, holding my breath and staying upwind. Then I'd run and let
the generated hydrogen cyanide do its work. A few breaths of
hydrogen cyanide causes death in about a minute and it takes only
100 parts per million of the gas in the atmosphere, even with
protective clothing.
If it were a nearly windless night, I'd punch holes in the
tops of the cans. One by one, I'd pour in the acid, cap the cans,
and throw them into the group. Then I'd flee upwind and lurk around
for a couple of hours until the Killer Caravan was no more and the
gas had wafted away.
Of course, this would wipe out the women and kids. But I'd
consider them doomed anyway. Even so, would you rather it had been
you and yours? Just imagine if Rev. Jim Jones had led his 900
crazies against your homestead. Would you care what happened to any
segment of that weird pack? If you would, you don't have a chance.