Roger Chapman explained on 03/03/2010 :
FWIW I have just checked back through my records for the last few months and
we had quite a bit of rain in November. The largest 15 minute record was 0.16
inches and the biggest total over an hour 0.43 inches which included 0.14
inches in 15 minutes. However we had a cloudburst some time ago and IIRC
three quarters of an inch fell in under 10 minutes and almost an inch in 15.
The road turned into a raging river part of which overflowed onto my
neighbours drive washing away the gravel surface and flooding his garage.

Apart from the odd obvious glitch in stored data, those are fairly
similar to the peaks I have seen.

The peaks do not tend to cause the flooding, it is more a case of lots
falling and over a long period to cause the floods. Also the ability of
the ability of the ground to absorb the water. Already moist ground
soaks up water better than perfectly dry ground, just like an already
moist cloth absorbs water more easily than a dry one.

My garage floor has a tendency to suffer the slab flooding, which
happens once maybe twice a year. I have tried to correlate data from my
rain gauge to predict when it might be liable to have flooded, but
there are so many variables it is almost impossible to work out. All I
have been able to determine is that if the ground is already sodden and
is then hit by a sudden really heavy down pour, it quite possibly will
be wet next time I go in there. My occasional flood will be similar to
your tank flood.

My solution so far has been to improve the drainage around the garage
base as time permits. It used to flood much more frequently, but the
fact that it still does rarely flood means I have a little more work to
be done.



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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk