Editing Trinity House (section)

==Trinity High Water==
[[File:JosephHuddartZh.jpeg|thumb|[[Joseph Huddart|Capt. Joseph Huddart]] {{postnominals|country=GBR|size=100|FRS}}, Elder Brother, set the Trinity House stones]]
'''Trinity High Water''' (or '''High Water, Trinity Standard'''), abbreviated '''T.H.W.''', was a [[vertical datum]] used for legal purposes in the River Thames and informally over a much wider area.  Though not thus defined, it was about {{convert|12|ft|6|in}} above mean [[sea level]].<ref>{{cite journal|last=Redman|first=John Baldry|year=1877|title=The River Thames|journal=Minutes of the Proceedings of the Institution of Civil Engineers|volume=XLIX|pages=88–9|doi=10.1680/imotp.1877.22501|url=https://babel.hathitrust.org/cgi/pt?id=pst.000052356438&view=1up&seq=100|access-date=15 January 2020}}, p=88.</ref><ref>{{Cite web|url=https://www.ordnancesurvey.co.uk/benchmarks/|title=Ordnance Survey Benchmark locator|access-date=2021-12-21}}</ref>

The concept had its origin in the [[List of acts of the Parliament of Great Britain from 1800|London Dock Act 1800]] ([[39 & 40 Geo. 3]]. c. xlvii)<ref>The short title of "An Act for Making Wet Docks, Basons, Cuts, and other Works, for the greater Accommodations and Security, Commerce, and Revenue, within the Port of London" ([[39 & 40 Geo. 3]]. c. xlvii) (20 June 1800).</ref> which authorised the making of the [[Wapping|Wapping basin]] of the [[London Docks]] and specified its minimum depth ''ie.'' over the [[sill (dock)|sill]].  At that time there was no [[Ordnance Datum]] or other accepted vertical benchmark.  Therefore, the 1800 Act defined the benchmark for this dock as "the level of the river at low-water mark".  Since opinions about this might vary, it added: 

{{Blockquote|The same shall be settled and determined by two of the Elder Brothers of the Trinity House, within three calendar months next after the passing of this Act, who shall certify the same in  writing  under their hands and seals.}}

Accordingly, Trinity House — in the person of [[Captain (naval)|Captain]] [[Joseph Huddart]]<ref name="Hall1943">{{cite journal|last=Hall|first=William Bertam|year=1943|title=The Origin and History of Trinity High Water|journal=Journal of the Institution of Civil Engineers|volume=21|issue=1|pages=30–34|doi=10.1680/ijoti.1943.13961|url=https://www.icevirtuallibrary.com/doi/pdf/10.1680/ijoti.1943.13961|access-date=16 January 2021}}</ref> — set a stone in the external wing wall of the [[London Docks#Physical description|Hermitage Entrance]] to the [[London Docks]].<ref>More precisely (for the London Dock did not yet exist), in an existing wall later incorporated into the dock.</ref> It was inscribed {{blockquote|Low water mark is 17 feet 10 inches below the lower edge of this stone, settled by the Corporation of Trinity House Aug{{sup|t}}. MDCCC}} Similar stones were afterwards set for Wapping and Shadwell entrances.

This established a benchmark which was supposedly extended for further purposes ''eg.'' the sill heights of other docks and for high water also.<ref>{{cite journal|last=Redman|first=John Baldry|year=1877|title=The River Thames|journal=Minutes of the Proceedings of the Institution of Civil Engineers|volume=XLIX|pages=88–9|doi=10.1680/imotp.1877.22501|url=https://babel.hathitrust.org/cgi/pt?id=pst.000052356438&view=1up&seq=100|access-date=15 January 2020}}</ref>

Trinity High Water Mark was much used as a datum in [[London]] for legal purposes.  It was required to be marked on all drawings of property adjacent to the river when submitted to the [[Thames Conservancy]].  As another example, the minimum height of river walls were specified in feet and inches above T.H.W.<ref>{{cite book|last=Adams|first=Henry|year=1913|title=Practical Surveying and Elementary Geodesy|publisher=Macmillan|location=London|url=https://babel.hathitrust.org/cgi/pt?id=uc2.ark:/13960/t16m34740&view=1up&seq=150|access-date=15 January 2021}}, p.134</ref>  The benchmark was used in other contexts, such as "Luton is 400 feet above Trinity high-water";<ref>{{cite book|last=Prestwich|first=Joseph|title=A geological inquiry respecting the water-bearing strata of the country around London, with reference especially to the water-supply of the metropolis|publisher=Oxford|year=1851|page=141}}</ref> the elevations of water reservoirs;<ref>{{cite book|last=Cresy|first=Edward|title=An Encyclopædia of Civil Engineering: Historical, Theoretical, and Practical |volume=I|publisher=Longmans|year=1872|page=1884}}</ref> depths in the Geological Survey (London Basin);<ref>{{cite book|author=H.M. Stationery Office|title=Memoirs of the Geological Survey of Great Britain and the Museum of Economic Geology in London|volume=4|issue=1|year=1872|page=566}}</ref> the depth of an archaeological find;<ref>{{cite wikisource | last1=Owen | first1=Richard | title=Antiquity of man as deduced from the discovery of a human skeleton during the excavations for the East and West India dock-extensions at Tilbury, north Bank of the Thames | wslink=Antiquity of Man as Deduced from the Discovery of a Human Skeleton | publisher=Van Voorst | year=1884 | page=3 | firsticon=yes | noicon=yes }}</ref> and for railway elevations.<ref>{{cite book|last=Walker|first=James|title=Report ... on the Proposed Lines for a Northern Railway|year=1835|publisher=W.N. Knight|page=3}}</ref><ref>{{cite book|last=Mogg|first=Edward|year=1841|title=Mogg's Great Western Railway and Windsor, Bath, and Bristol|publisher=E. Mogg|page=23}}</ref>

Despite the importance of the Trinity Standard benchmark for legal purposes, it appears that there were discrepancies, some of them grave. Inconsistent standards purporting to be T.H.W. existed.<ref name="Hall1943"/>  Some stones set by Captain Huddart afterwards could not be found.<ref>{{cite web|title=On This Day in Trinity House History – 20 June|work=Trinity House History|date=20 June 2014|url=https://trinityhousehistory.wordpress.com/2014/06/20/on-this-day-in-trinity-house-history-20-june/#:~:text=Sir%20James%20Douglass%20Engineer-in-Chief%20Exactly%2065%20years%20later%2C,Docks%2C%20but%20only%20one%20stone%20has%20been%20found.|access-date=15 January 2021}}</ref>

Eventually, it was deemed by the [[Port of London Act 1968]] to be a level having a value of {{convert|11.4|ft}} above [[Ordnance Datum Newlyn]].<ref>*{{cite web|title=Chart Datum and Standard Levels in the Port of London|website=Port of London Authority|url=http://www.pla.co.uk/assets/PLA_TIDEBOOK__2009_30.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.pla.co.uk/assets/PLA_TIDEBOOK__2009_30.pdf |archive-date=2022-10-09 |url-status=live|access-date=15 January 2020}}</ref> and thus the connection with the Trinity House marker stones was abandoned.