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.

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

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

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.

On 11/08/2018 09:23, N_Cook wrote:
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, 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


Â*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.



Sorry Nick, but I have no intention of getting into hydraulic theory in
this group. If you are really interested then I suggest you go to your
local library and get hold of one of the 1200 page tomes on the subject.

Just to put your mind at rest on one thing. Where you have the vertical
junction between the pipe and the riser, turbulent flow will be present,
and to my knowledge no one has yet come up with a set of equations (or
even a half accurate computer model) for those conditions. The equations
for laminar low in similar conditions are horrendous enough, thank you
very much.

One further point to really confuse you. If you consider an 18" circular
pipe carrying water at a depth of 6", and then consider an 18" circular
open topped channel 9" deep with 6" of water in it, the flow equations
will come up with two completely different answers due to the friction
between the air and the surface of the water because of the different
conditions affecting that air.

It's really a very simple subject made complicated by the application of
science. Basically, with no added external forces, water flows downhill.

jim

On Friday, August 10, 2018 at 11:40:14 PM UTC+1, 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, 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

An interesting point

Graham
Penzance

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

An interesting point

Graham
Penzance


Yes, I was not aware of that aspect of "Coverack" type flooding
incidents. I've circulated that to the others in our local flood action
group.
There is so much of that sort of stuff that emerges that is not on EA
sites, that is not immediately obvious.
Like spend many thousands on marine flood measures and you compound the
problem/severity of landward intense rainwater flooding from
surrounding high ground, bad storm-drain sea outlet flap-valve design,
cross-coupling of storm-drains and foul-water systems, only a certain
amount of water depth you can keep out of standard brick-built houses
before structural failure etc etc

On 11/08/2018 09:23, N_Cook wrote:
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.


For the archives, by shining some torches in the air-balance holes I can
take pics, via the remaining vent, of the inside and determine
photogrametrically the proportion of water going from .225m pipe to .3m
lamphole and height of any water rising up the lamphole and the height .
of any water in the manhole, could not get anywhere with flash. With a
bonus of a photographic record.
Curiously and usefully there was a tell-tale of the exceeded height
reached at some such event after January 2014, of a piece of toilet
paper caught on a foot-plate, not there when a CCTV crew inspected then.