One end of the Grand Union Canal (Grand Junction Canal – Main Line) is at Brentford on the
River Thames in west London, where the canal follows the engineered course of the
Brent. The double Thames Lock at Brentford separates the
Tideway administered by the
Port of London Authority from the River Brent/Grand Union Canal, administered by the
Canal & River Trust. The locks on the canal are partially numbered: numbered consecutively south of its turn-off for Leicester, Braunston Junction. Thames Lock is lock number 101. ,
West London. Photo taken in twilight at the peak of a
spring tide For more than upstream of Thames Lock, the canal and the Brent are one and the same, and the waterway is semi-tidal until the double Gauging Lock (lock 100) at Brentford. Just upstream of the Gauging Lock was a large
canal basin, now known as
Brentford Lock, from which the canal covers more distance passing under Cornelius Bridge, Brentford Railway Bridge, and the Great West Road bridge and through two more locks. The river and canal part at the base of the
Hanwell flight of locks (92–97), after which it traverses
Three Bridges, London, Isambard Brunel's final project. Two more locks take the canal to
Norwood Green. It then heads westward over level ground through
Southall,
Hayes and
Yiewsley until it reaches the gentle valley of the
Colne. Three miles (5 km) from Norwood on this long level is Bulls Bridge Junction, once the site of the
Grand Union Canal Carrying Company's main dockyard. At Bulls Bridge, the
Paddington Arm branches off to the north and runs to join the Regents Canal at Little Venice (see below). Just before Uxbridge is
Cowley Peachey Junction, where the
Slough Arm branches off westward. At suburban Cowley, before the 1930s a rural village, the canal begins to climb the valley of the River Colne north north-west into the adjoining town of
Uxbridge. After Denham and
Harefield villages, it passes to the south of
Rickmansworth. Here it merges with the Rivers Chess, Colne and Gade. After Rickmansworth, the canal follows the valley of the
Gade, passing the site of
Croxley paper mill. The canal skirts
Watford through
Cassiobury Park, passing under the
M25 motorway as it approaches
Kings Langley. Locks become more frequent as the climb into the
Chiltern Hills steepens. The original four locks here were replaced in 1819 by five shallower ones to alleviate problems with water supply to the nearby paper mills. This realigned the canal to the south of its former course; the locks here are still referred to – without irony – as "The New 'Uns" by traditional boaters, and the term has been passed on to a new generation of canal users. After
Kings Langley and
Apsley – the site of more former paper mills – the canal passes the town
Hemel Hempstead and Boxmoor Common. From here the canal follows the course of the
River Bulbourne through
Bourne End with the well-known
swingbridge at Winkwell, and the "Port of
Berkhamsted, a small compact town". At
Cow Roast Lock the canal reaches the 3-mile (5-km) summit at
Tring in the Chiltern hills, having risen through 54 locks since Brentford. At the north-west end of the summit level is Bulbourne Works, where lock gates were manufactured until 2003 for the southern canal network. Half a mile (800 m) further on, the canal reaches the top of the Marsworth flight of seven locks, which begin the descent to the
Vale of Aylesbury. A
Wendover Arm branches off westwards from the summit level under a bridge adjacent to Marsworth Top Lock and is currently navigable for just over a mile to moorings and a
winding hole; it has restoration project to extend it back to Wendover. This part of the canal in parlance used by natives and canal staff was "the withered arm" and in fact was only really "opened" to allow the pumping station there to pump water into the uppermost level. A few hundred metres beyond the bottom lock of the flight, the
Aylesbury Arm branches off to the south west. The Grand Union descends gradually by interspersed locks, past the villages of
Cheddington, Horton and Slapton until it reaches
Leighton Buzzard. Traditionally this section of the canal is called "Slapton Fields" or just "The Fields" by boaters. A few miles further on, a flight of three locks near
Soulbury marks the descent towards the valley of the
River Great Ouse. Aqueduct, Milton Keynes A few miles further on it enters
Milton Keynes at the outskirts of
Bletchley at
Fenny Stratford Lock, which is unusual in lowering the level by only . The next stretch of is on the level. There is a modern proposal to dig
a new arm from here to the Great Ouse navigation at
Bedford. North of the centre, it traverses the modern
New Bradwell Aqueduct, the first on the Grand Union in over 100 years. Leaving Milton Keynes at
Wolverton, the canal runs on a high embankment before passing over the Great Ouse at
Cosgrove aqueduct (the "Iron Trunk aqueduct"), the first
cast-iron "trough"
aqueduct in England. After rising through Cosgrove Lock, (and passing the start of the abandoned
Buckingham Arm) another long level section brings the canal to the bottom of the
Stoke Bruerne flight of seven locks. At the top of this flight is the
Stoke Bruerne Canal Museum followed shortly by
Blisworth Tunnel, at one of the longest of UK canals. Once clear of the tunnel, the canal passes
Blisworth village and reaches
Gayton Junction where the
Northampton Arm branches off to the east. This arm has 17 narrow locks as it descends to join the navigable
River Nene (see below). The long level stretch continues past several villages including
Nether Heyford and
Weedon Bec and is very rural in character. At
Whilton, the canal reaches the bottom of the Buckby flight of seven locks which raise it to
Braunston summit the village of which
parish is away. Beyond the top lock is
Norton Junction where the Leicester line (not strictly a branch) heads off north. A few miles further on the canal passes through the 2040-yard (1865-m)
Braunston Tunnel, which pierces a low range of hills that are part of the
Northamptonshire uplands. The canal then drops down the Braunston flight of six locks until it reaches Braunston Junction having covered just over . == The Birmingham "main line" ==