On 10/08/2018 16:46, N_Cook wrote:
On 10/08/2018 14:04, wrote:
Ominous dark cunims, gusty winds, heavy bursts of showery rain - the
weather has changed in the south-east at last!

Molesey, SurreyÂ*Â* 2pm BST - very dark even though only 7 oktas, heavy
rain just starting, thunder to south.

The view westwards from The Shard is often informative weatherwise and
here's the link, either for live views or select previous times.

https://www.theviewfromtheshard.com/...shard-london-3


The eastward view is obviously best for departing showers / storms today.

If drought stricken trees could smile..... autumn beckons?

Julian

Molesey,Â* Surrey.


And the seemier side in Southampton of an intense rainstorm this
afternoon, of 8mm of rain in 15min at the local rain-gauge.
The pressure hence height rise in the local sewers
Time, depth of water (sewer diameter 0.45m)
13:58 BST, 0.22m
14:00, 1.41m
14:02, 1.35m
14:04, 0.58m
14:06 , 0.41m
rise of about 1.2m in 2 minutes, another 0.6m rise and the level of the
bogpan U-bends locally.
29 May this year measured 1.34m rise for a similar storm


From your figures, I assume the depth was measured at a manhole, and
that at 14:00 the water was above the top of the pipe.

Just for information, a concrete pipe (most 18 inch pipes these days are
concrete) will carry less water when it is full that it does when only
three-quarters full. This is due to the friction exerted on the full
circumference of water in the pipe in contact with the pipe wall itself.
At three-quarters full, less water is in contact with the pipe, and the
top of the water experiences virtually no friction from the air above
it. That is why flood waters rise so quickly, but take a lot longer to
drain away.

jim