New Southgate Gas Works

New Southgate is a largely residential suburb of North London that has portions in each of three London boroughs - Barnet, Enfield and Haringey. It broadly aligns with what used to be called Colney Hatch. 

The new name was adopted in order to distance the district from the lunatic asylum, built in 1851, with which Colney Hatch was once synonymous. There was little here until the arrival of the Great Northern Railway.

To the south of this was built, in 1858, the New Southgate Gas Works. The works ultimately included three gas holders, the largest of which (pictured) was built in 1912, hard by the North Circular Road (opened 1910, completed about 1930). 

The works closed in 1972, and the two smaller gas holders were dismantled. The remaining holder was decommissioned in 2001, but survived until 2020, when it was dismantled by Erith Demolition, for National Grid.

Falkirk Wheel

The Forth and Clyde Canal (built 1768 to 1790) and the Union Canal (built 1818 to 1822) were once linked by a flight of 11 locks at Camelon, near Falkirk, that carried the former 112 feet up to the latter. These fell into disuse in 1933. When the Millennium Link project set out to restore the two canals and rejoin the Clyde and the Forth, a task achieved in just three years between 1999 and 2001, a new means of connecting them was required.

The Falkirk Wheel, built 2000 to 2002, was the solution. The world's first rotating boat lift, the wheel forms part of a £20m complex comprising a 551 feet long tunnel that carries the Union Canal under the Antonine Wall, a 341 feet long aqueduct that brings this higher canal to the wheel, and the lift down to a large basin that itself gives onto the Forth and Clyde Canal. The site is just under two miles from the original locks, and was previously home to a redundant tar works.

The wheel itself is 115 tall and 89 feet long, and bridges 82 vertical feet between the two canals. Designed by Nicoll Russell Studios, of Dundee, it employs two interlinked mechanisms that serve to keep level the rotating gondolas, and the water and boats within them, whilst using the bare minimum of power. Just 1.5kW, about that needed to boil six kettles of water, is required to turn the wheel through 180 degrees, yet the transition takes just five minutes.

The first mechanism is the ten hydraulic motors that drive the axle, 13 feet in diameter, and thereby a central cog, 26' 3" in diameter, fixed to both the axle and the end support of the aqueduct. As the axle turns, smaller rotating cogs, either side of the central cog, transfer the drive to cogs mounted inside of the propeller-like arms of the wheel, one each side. These outer cogs rotate at the same speed as the central one, being the same size as this, but in the opposite direction to the axle and the wheel as a whole.

The second mechanism, a series of bogie wheels at each end of the 82 feet long gondolas, run on curved rails mounted within the propeller arms. Gravity largely enables this second mechanism alone to keep the gondolas horizontal, but wheel friction and sudden displacements within the gondolas could jolt these out of alignment. The non-powered mechanism of five cogs keeps everything safely aligned.

From boat entry to boat departure, the trip through the lift takes just 15 minutes. Once boats have entered/departed the gondolas, paired steel gates move from a prone position to an upright one, closing off the gondolas, the aqueduct at the top, and the basin at the bottom. Rubber seals spring out along the sides and bottoms of the paired gates and the water between these is pumped out. When the half turn is completed, water is pumped back into the space between the paired gates, which then flap downwards to enable boats to depart/enter the lift.

The speed, elegance and efficiency of the wheel belie its scale. The complete structure weighs in at 1,772 tons, of which 98 tons is in the form of the two gondolas, and 492 tons in the form of the carried water and boats. In accord with Archimedes' Principle, boats entering the gondolas displace their own weight in water, although a system of sensors, valves and bypass pipes maintain the water levels in the aqueduct and basin, so as to keep those in the gondolas consistent. There's a maximum variation in water height between the paired gondolas of three inches.

The steel fabrication was undertaken by Butterley Engineering, of Ripley. The structure is bolted together, not welded, to give it greater strength. 15,000 bolts were driven through 45,000 holes, the punched-out weight of which was just under seven tons. A joint venture between Morrison Construction, of Scotland, and Bachy Soletanche, of Ormskirk, acted as main contractor. The wheel itself, fabricated offsite, was erected in just six days.

Arup Consultants and Tony Gee and Partners acted as civil engineers. Much clever materials thinking went into the engineering. The elegant hoops that support the aqueduct, for instance, are of steel-reinforced concrete up to the point that carries the weight of the trough, but of GRP (glassed-reinforced plastic) above that. The canal engineers and navvies of old would be proud.

Deflated Gas Holders

Gas holders, also incorrectly referred to as gasometers - they don't measure anything - were once a common sight in UK towns and cities. They provided a means to store gas, and to maintain the downstream supply at what is called district pressure.

The first gas holder in the UK was erected in 1798, at the Soho Manufactory, in Birmingham. The water-sealed telescopic form, which came to dominate, was invented in 1824, the first constructed in Leeds. The earliest telescopic holders had two lifts, supported by columns. Later models had up to four, frame-guided, lifts. In 1890 William Gadd, of Manchester, invented the spiral-guided gas holder, the helical runners of which obviated the need for an exoskeleton. The last of these was built in 1983.

The gas was stored at near atmospheric pressure, the necessary weight applied by the heavy cap. The tank containing the gas floated in a reservoir of water, which provided the necessary seal, and rose and fell as the volume of stored gas either increased or decreased. A lipped channel around the base of each lift picked up water from the reservoir as the gas holder rose, thus maintaining the seal.

The holders were often sited next to plants producing town gas from coal, but were steadily adapted to store natural gas. Typical volumes for the larger holders, up to 200 feet in diameter, were 1.8 million cubic feet. As a nationwide network of pressurized pipes and regulators for provision of natural gas was developed the holders increasingly became redundant. A few still serve to balance pressure in the pipe network, but in 2013 National Grid announced plans to steadily remove the gas holders of England and Wales. SGN has similar plans for those in Scotland.

The three gas holders visible from the Aston Expressway, Birmingham, were decommissioned between 2009 and 2011. The conjoined pair, erected in 1885, were once part of the Windsor Street Gas Works; sometime in the 1980s they were painted in the claret and blue colours of nearby Aston Villa Football Club. National Grid has been granted permission to demolish all three holders, which are expected to disappear in 2020.

(Second photograph by Abi Smith.)

Standedge - Longest, Deepest, Highest

The Standedge canal tunnel, on the Huddersfield Narrow Canal, is one of four parallel tunnels - the other three are railway tunnels - that run through the Pennine hills between Marsden, West Yorkshire, and Diggle, Greater Manchester. The Act of Parliament authorising the canal's construction was passed in April 1794. Benjamin Outram, acting as consulting engineer, estimated the total cost, including the tunnel, at £178,478, and the construction period at five years. Nicholas Brown undertook the necessary survey work, which foresaw a tunnel of 5,456 yards.

Outram was appointed site engineer, and Brown surveyor and superintendent. The tunnel was driven from both ends at once and from intermediate shafts. The intermediate workfaces were abandoned in the autumn of 1796. This change, greater water ingress than expected, and difficult geology, slowed progress. The rest of the canal was completed by 1799, and horses used to transship cargo over the Pennines between the completed sections. Tenders for work on the tunnel went unlet, and it was found that the headings had been driven several feet higher from the Diggle end than from the Marsden (above). In 1801 Outram resigned and Brown was dismissed.

In 1806 a new Act of Parliament provided for the raising of further finance. Thomas Telford was consulted, and in 1807 drew up a plan for completion. This corrected for the crooked workings driven from the intermediate headings: the tunnel has noticeable bends. Finally completed in March 1811, and at a cost of £123,803 for the tunnel alone, this was 5,445 yards (3.1 miles) long, 636 feet below ground at its deepest, and 643 feet above sea level. The longest, deepest and highest canal tunnel in the UK.

In 1822 the tunnel was extended 11 yards at the Marsden end, to accommodate reservoir works. In 1893 it was extended again, by 242 yards, this time at the Diggle end, so that the 1894 railway tunnel could be carried over it. These additions supposedly made the tunnel 5,698 yards long, although modern survey techniques make the total length 5,675 yards (3.2 miles).The tunnel has no towpath, which required the canal boats to be legged through. This was tough and dangerous work, not least given that large parts of the tunnel were left unlined, with the native rock jaggedly proud of the ever-changing overall profile. Some sections are lined with rough-dressed stone, and some with brick.

The Huddersfield and Manchester Railway bought the canal in 1846, which enabled the first railway tunnel, completed 1848, to be driven without the need for ventilation or extraction shafts. Drainage adits (above) drain the higher railway tunnels into the canal tunnel, and gantries (below) link the former. When the railway tunnels were driven much strengthening work of the canal tunnel was required in the form of heavy brick arches.

The tunnel officially closed in 1944, when maintenance ceased. Dilapidation prevented all but a couple of later exploratory journeys. A £5m restoration project in the 1990s set about reopening the canal in its entirety. Shotcrete and rock-bolting were used to stabilise some of the unlined sections of the tunnel. This reopened in May 2001, after 57 years of disuse. Boats were tugged through by electric tugs, but since 2009 have been able to transit the tunnel under their own power, with a pilot aboard, and chaperoned by a vehicle driven through the adjoined first railway tunnel (below). The journey takes about two hours.

Brogyntyn - Home Farm, c.1894