Post by t***@smartcomsoftware.comRemember that chart datum is referred to the local sea level, and not the land level. In general, the difference between the two is measured at a tide gauge station, and interpolated between. Until recently, mapping between chart and land vertical datums has been vague and messy, but in some countries this has recently improved significantly. For more on this in the UK, google VORF, a project by the UKHO and University College London to accurately define the chart datum with respect to the GPS geoid and the Ordnance Survey datum.
Interestingly, when all the countries in the North Sea compared their datums (all nominally LAT), none of them actually matched up!
Tim
Post by N_CookLand based datum of Ordnance Survey and marine datum of the UK
hydrographic office.
A noteable local flood event in 1924 with contemporaneous newspaper
reports of land flooding to a specific height of 3 foot = 0.9m above a
still extant specific spot and other info is consistent with that depth.
That extreme tide height in 1924, converted to metric is 5.6m.
5.6m is also quoted officially as the next record high tide recorded in
Southampton in 1999, 1924 and 1999 both recorded as 5.6m.
The problem is that the water in the current marine system would have to
reach a height of 6.0m (+/- 0.1m) for the same 3 foot of flooding.
We are in the part of the world that is sinking to compensate for the
north of the UK, which is rebounding from the last Ice Age and climate
change is supposed to be increasing average sea level. The road surface
has not been increased in spot height more than 0.1m over that time.
What to believe, newspapers or hydrographic office or how to interpret
these data?
Local, to me, BBC South looks as though they will be doing a 10 minute
slot in the Inside Out program on this stuff.
Including Vectis Tavern, Cowes, "tide gauge"
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probably 17 Dec 1989 and 22 Oct 1984 and
battern part obscuring the lower one Date, probably 02 Dec 1909
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Anyone got an Infra-red camera to borrow to non-destructively discover
the covered mark/s?
It's reported to me by 3 different people that there used to be a mark
at chest high, but no one can remember the date , probably 27 Nov 1924
or 14 Nov 1931 or even 01 Jan 1877. Anyone aware of pictures showing
the inside of the Vectis Tavern before the bar was moved and anaglypta
wallpaper covered over the higher markings? (or IR camera and heat source)
Or other info concerning Cowes or IoW or Solent area dates/heights
(indirectly from pics) of flooding before 1989?
Google images surprisingly shows no functions / events inside the Vectis.
Second pillar in from the High St and on that face facing the High St,
inside the bar counter.
I've recently been researching in newspaper archives for extreme marine
floods around the Solent, ie Solent-wide , surge-type, not very
localised events. With depth overland of inundation as a measure of sea
"storminess", less now than centuries back. Two academics have come to
the same conclusion , from a different direction and different records.
The Vectis Tavern pub, Cowes, IoW used to have the levels of extreme
tides reached when it flooded the pub, marked on a pillar in the bar.
With renovations in the last 10 years or so only the bottom marks can be
seen now under the counter. The present landlord let me take these pics
a month ago.
It is of academic significance , because of confusion over measurement
datums, what these historic tide levels were, linked to one specific site.
It's reported to me by 3 different people that there used to be a mark
at chest high, but no one can remember the date , probably 27 Nov 1924
or 14 Nov 1931 or even 01 Jan 1877.
The floor of the pub has been there since 1400s (scheduled buildings
register, before becoming a pub in 1700s, why you have to go down steps
into the main bar area) and this pillar since the Victorian era .
The floor is at the level of the normal astronomic tide height of spring
tides. This central south region is supposed to be sinking (balancing
north rebound after the ice age) plus sea level rise would suggest more
extreme marine flooding.
The 1860s 25 inch scale OS map shows the VT as not including the Town
Quay half then, presumably a wall dividing then rather than a pair of
pillars , so the earliest dates noted below could not have been recorded
on the pillar.
The 1909 mark is 0.64m above the floor and the 1984 0.74m and 1989 0.95m
but which date is the topmost covered-over/erased one and its height,
should be about 1.2 to 1.4m off the floor.
Theoretical set of marks with heights determined from newspaper reports,
so only approximate
19 Jan 1804, 1.35m (reported in 1804 newspaper as highest tide for 30
years )
27 Nov 1924, 1.25m
14 Nov 1931, 1.2m
01 Jan 1877, 1.1m (Mr John White newspaper quote of Cowes tide-height
reference and 1818 one)
04 Mar 1818 , 1.05m
17 Dec 1989, 0.95m (actual mark, VT landlord comment in local press)
27 Nov 1954, 0.95m
25 Dec 1912, 0.9m
26 Dec 1999, 0.85m
08 Oct 1960 , 0.8m
22 Oct 1984, 0.74m (actual mark, VT landlord comment in local press)
02 Dec 1909, (actual mark) , 0.64m
22 Oct 1909, 0.55m
12 Jan 1978, 0.45m
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Hampshire Advertiser, 03 Jan, 1877.
So far I have more faith in the 1877 reported statements of Mr John
White of Cowes than local wrongly ascribed datums "official" historic
extreme tide records , which place the tide height reached in the 1924
flooding as being the same as 1999 flooding , when there is a 0.4m
difference, and no mention of the 0.1m higher tide in 1989 , just
because their tide guage was out of action then .
As he or his family must have had daily contact with tide and ground
level for more than 59 years he was probably the "John White of Cowes"
who built "specialised lifeboats " at Cowes and founded in 1805 what
became John Samuel White shipyard of Cowes. A lot of JS Whites records
ended up at the Beckford Rd , Cowes Library, whether this tide record
probably not, not at the Newport Record Office anyway.
Also Beken photographs of flooding , PV98 catalogued as 1899 date
has the wrong clothing for that time and no blurring of the rowers in
the boat in the High St outside the National Provincial Bank, probably
1920s to 1930s and another with Morris J van maybe 50s is undated
totally, PV117 dated 1920, number 42734 of 1960 and other
flooding pics in their catalogue of Medina Rd, sea front etc
42733,PV102,PV71,PV99/100/101, PV56,PV71.
Useful tabulation of flooding events recorded in the Times on
http://dro.dur.ac.uk/1072/1/1072.pdf
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Echo 27 Nov, 1924 and Hampshire Advertiser 29 Nov 1924.
For anyone who thinks the 1924 tide height was the same as 1999, you
need a goodly amount of flood water to cause domestic furniture to float
around, stop people leaving upper stories of houses and no reports of
houses in Adelaide Road , St Denys, flooding in living local memory.
I dropped in Southampton Archives and the "Fundamental " Fundamental
Bench Mark,
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From 1868 Series 1 252 scale map, only to 1 decimal place placed on
maps, height of bench mark then 75.6 ft
Later height on the brass plaque screwed over the original bench mark
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74.35 ft (no one has tried unscrewing these screws, perhaps because of
the notice saying damage to this is a
criminal offence).
Then the Penna Liverpool - Newlyn height difference of about .02m
from analysing the colouring, gives the error picked up in newspaper
reports as 0.40 +/-0.02m until OS reveals a 2 places of decimals First
Geodetic Levelling height for this bench mark .
http://www.cage.curtin.edu.au/~will/GJI_ODN_slope.pdf
I find it very disturbing that this error in the record is not stated
anywhere that I've found. I can only assume
the same error applies to other ports around the UK as it is independent
of Southampton using their own
local PLWD datum, as that is stated in the contemporaneous record as
being 7.48 ft below the then Newlyn
datum. So the1924 flood was 6.0m +/-0.02m , not the 5.6m recorded in the
official tide-height history of Southampton. They would not have been
using the Second Geodetic Levelling height in 1924.
No reason to believe the situation of wrongly recorded flood histories
does not apply to other ports and historic
tides.
Southampton Archives image,
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, as "SC/E/6/24/156" is indexed as flooding in Clarence St,
Northam. From another image showing what is called New Liberal Club,
Northam, shows the club
and a shop , and general house forms that match , behind the cart in
that image, and then
from street directories it is probably housing blocks, shop and Evan's
Liberal Club, 6-8 Belvedere Terrace,
Northam. Two boys in sunday best and Eton Collars, girl moved head
quarter of a turn in exposure, no ripples in the water, 10 foot away
poor focus, and people hanging out of each upstairs window on the right.
Was the interest because no one had seen a camera before and the date
was much earlier, say 1877?. Gas lighting been in southampton since
1829, same lamps were shown in a dated 1921 picture of that area. The
archivists have suggested dates of 1900 or 1910.
Then from OS street spot heights and this FGL-SGL OS correction of 0.4m
, the flooding was to 6.0m +/-0.3m , the errror range because OS maps of
the time only gave integre spot heights in feet.
If the cart in the Belvidere Terrace pic , viewing the original sepia
postcard in Southampton Central Library, shows the name CHaMberS
and larger letters below fishmonGEr (discernable placed as large letters
here, although brushes and pans on it) then John Chambers was at number
10, 1897 to 1900, maybe a bit longer but not a continuous set of Kellys.
As postcards like this were produced by professional photogtraphers ,
there was a commercial photographer AG Butler, 25 Northam Rd at that
time. So now 2.5 of 3 different pointers to
the historic datum correction for Southampton being 0.4m, if
not 1924 then another , unknown date, of similar flooding extreme height.
Another image out there of the Cooper' Arms Clarence St, William St,
shows only about a 5.6m flood
of 25 December 1912 , quote from the Echo
"Priory Road the unusual sight was witnessed of a small boat ferrying
stranded pedestrians to and fro like a gondola in Venice"
