(Presuming a global flood, the rain is not necessarily overwhelming.)
(Apologies for the roundabout method of calculation)
I fail to see what's so overwhelming about 15 feet per hour, unless those 15
feet all come at once every hour! Let's turn this into metric, for convenience: 15 feet
per hour is equivalent to 15*30 = 450 cm per hour, which is 7.5 cm per minute, or .125 cm per second.
Considering that the biggest raindrops have a terminal speed of 8 meters per second
(I read it on the Internet, it must be true :-) ), and a
mL of water is exactly a gram (by definition, apparently), we can use simple math and physics
to show the force
needed to hold up a roof under the impact of the rain.
Let's use a 10cm by 10cm square as our sample area, and use 1 second for our sample time. If we give it a height equal
to the height of rain falling in one second, we can find the volume of rain that
falls on that square for that second. So, take 10cm*10cm*0.125cm, which gives us 12.5 cm^3 in volume.
Conveniently, 1 cm^3 = 1 mL, and 1 mL of water = 1 g. So, 12.5 cm^3 translates
to 12.5 grams, or 0.0125 kg.
The rain falls at 8 meter per second. Next, we find the momentum.
P = mv = (0.0125 kg)(8 m/s) = 0.1 kgm/s. Momentum is also
force times time (P = Ft), which is equivalent to F = P/t. Since we are using a 1 second interval,
we get 0.1 newtons for every 10cm by 10cm area, or 1/100th of a meter squared.
Multiply by 100, we and get
10 newtons for every meter squared (those of you who know physics can already tell
by now that this force is not overwhelming). Now, the Bible states the dimensions of
the presumably rectangular ark. The roof is 135x22.5 meters (Genesis 6:15), assuming it's flat.
This makes an area of about 3040 meters squared.
So, 10 newtons times 3040 gives us about 30400 newtons applied to the entire ark. Divide this
by 9.8 (how many Newtons a 1-kg object weighs on Earth), and we can see
what equivalent mass sitting on the ship would exert that force. The answer
is 3100 kg. Even with the upper limit of 20 000 feet over the 40 days, it is 4300 kg.
These extra "weights" are not very significant (A few extra elephants' worth on a large ark).
However, I don't know enough about
the shape of the roof (top surface) to remark on the layer of water that hasn't run off yet. If it's a flat
roof, I suppose you'd get some sort of parabola-shaped blob of water on top, which
might put a considerable extra strain on the structure. If it's a pointed roof, you
could expect a quick run-off, and the ark could then easily survive that load. In addition,
the rain would be deflected off a pointed roof instead of hitting head-on, which would lessen the vertical
load created from impact.
Erosion probably isn't a problem, since it is only rain (perhaps the layer of water that
has not yet run off would also serve to cushion impacts). The pitch that the ark was
covered with would probably keep the wood from getting waterlogged. Yes, I know that
buildings and vehicles have problems with only one foot of water per hour. Then
again, buildings and vehicles don't float. :-)
In addition, I have assumed that all the flood's water is rain. This isn't true, because
at least some water came from the "springs of the great deep", which I would interpret
as aquifers or something, but definitely not rain.
In conclusion, I would say that John Allen Paulos may be a victim of Innumeracy himself.
However, although excessive rainfall may be an invalid point against a global flood, I do have other reasons
for rejecting it (the global flood), namely:
- The Bible allows for a local flood.
See http://www.reasons.org/resources/books/genesisquestion/gq18.html
- I believe that God has stopped creating lifeforms (we are still in the seventh creation day of rest),
which
fits with an old earth creation view. There is no way that rapid
speciation could have happened in the short time after the flood if God didn't do it. Even
evolutionists aren't that optimistic about natural speciation. :-)