On 10/08/2018 23:40, jbm wrote:
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, Surrey 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, 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


Yes a manhole that connects the local (forgetting all pre-metric) 8 inch
sytem via vertical 12 inch lamphole (goes back to Victorian method of
jecking for blockages a lamp lowered through) into the 18 inch part city
wide sewer mainly from much higher ground.

If you happen to know the hydraulics. We know there is (there should not
be but a number of delapidations) cross-coupling between tidal-water
that is always in the storm-drain system at high tides , into the
foul-water local high-level sewer (the cascade noise at this
manhole,down the lamphole, increases at spring high tides).
We can monitor at this manhole but awkward geometry.
The pipe enters into a 4 inch wide chord of 8 inch pipe set in near
level concrete mid-level base of this manhole to the central lamphole
exit, the man accessible bit.
So as the height of water rises above the chord part , it fans out.
Needed is the geometry of flow at such a point, or even the technical
term for such delta/fanning flow, to get an idea from converting simple
height at the chord to flow in the 8 inch pipe at the top of spring
tides +surge events.
To get a table of sea-water level to flow in the local system.