2021

SP1976 : Bottom Lock Cottage, Knowle locks

taken 3 years ago, near to Knowle, Solihull, England

Bottom Lock Cottage, Knowle locks
Bottom Lock Cottage, Knowle locks
On the Grand Union Canal. The bridge to right of centre crosses over the remains of one of the original narrow locks that were replaced by five wide locks.
Bench Mark

Bench marks LinkExternal link were historically used to record the height above sea level of a location as surveyed against the Mean Sea Level data (taken at Clarendon Dock, Belfast, for Northern Ireland data, Newlyn in Cornwall for data in Great Britain and Portmoor Pier, Malin Head, for data relating to the Republic of Ireland). They were used as part of a greater surveying network by the UK Ordnance Survey, Ordnance Survey Northern Ireland (OSNI) and the Ordnance Survey Ireland (OSI). If the exact height of one bench mark is known then the exact height of the next can be found by measuring the difference in heights, through a process of spirit levelling. In this way hundreds of thousands of bench marks were sited all around the UK & Ireland from the mid 19th to late 20th centuries. There are several distinct types of bench mark:

- Fundamental bench marks have been constructed at selected sites where foundations can be set on stable strata such as bedrock. Each FBM consists of a buried chamber with a brass bolt set in the top of a granite pillar. See NG8825 : Dornie fundamental bench mark for an example. FBMs were used in Ireland as well as GB but those in Ireland do not have any surface markers, nor are they marked on standard maps.
- Flush brackets consist of metal plates about 90 mm wide and 175 mm long. Each bracket has a unique serial number. They are most commonly found on most Triangulation Pillars, some churches or on other important civic buildings. See J3270 : Flush Bracket, Belfast for an example.
- Cut bench marks are the commonest form of mark. They consist of a horizontal bar cut into a wall or brickwork and are found just about anywhere. A broad arrow is cut immediately below the centre of the horizontal bar. See J3372 : Bench Mark, Belfast for an example. The horizontal mark may be replaced by or contain a bolt - see J1486 : Bench Mark, Antrim.
Other marks include:
- Projecting bench marks such as SD8072 : Projecting Bracket Benchmark on St Oswald's Tower
- Bolt bench marks such as SJ1888 : OSBM bolt on Hilbre Island
- Rivet bench marks such as J3978 : Bench Mark, Holywood
- Pivot bench marks such as SJ2661 : Pivot bench mark on Leeswood Bridge

Bench marks are commonly found on older buildings or other semi-permanent features such as stone bridges or walls. Due to updated mapping techniques and technological advances such as GPS, bench marks are no longer maintained. Many are still in existence and the markers will probably remain until they are eventually destroyed by redevelopment or erosion.

Knowle Locks on the Grand Union Canal

There are five wide locks in the flight at Knowle on the Grand Union Canal. They provide a total rise of 41ft 10in (12·75 metres).
Originally there were six narrow locks here. During the extensive upgrading of the Grand Union Canal in the early 1930s these were replaced by the five wide locks in which pairs of boats could navigate together, side by side. Remnants of the original structures can still be seen to the east of several of the current locks.
Side ponds were installed alongside each lock in order to optimise efficiency in the use of water. Pairs of ground paddles can still be seen by each lock, though the sideponds are no longer in use.

The locks are numbered 47 to 51 starting from the bottom of the flight.


Creative Commons Licence [Some Rights Reserved]   © Copyright Chris Allen and licensed for reuse under this Creative Commons Licence.
Geographical Context: Canals Canal: Grand Union Canal Place: Knowle Primary Subject: Canal other tags: Flight of Locks Lock Cottage Click a tag, to view other nearby images.
1:50,000 Modern Day Landranger(TM) Map © Crown Copyright
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1:50,000 Modern Day Landranger(TM) Map © Crown Copyright
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Grid Square
SP1976, 46 images   (more nearby 🔍)
Photographer
Chris Allen   (more nearby)
Date Taken
Saturday, 24 July, 2021   (more nearby)
Submitted
Saturday, 24 July, 2021
Subject Location
OSGB36: geotagged! SP 1904 7604 [10m precision]
WGS84: 52:22.9240N 1:43.3019W
Camera Location
OSGB36: geotagged! SP 1902 7602
View Direction
Northeast (about 45 degrees)
Clickable map
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Image Type (about): geograph 
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