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Into the Megatron (1)

Most of us known about Megatron, a Victorian-engineered labyrinth of storm drains with cathedral-like brick archways and interconnected dark tunnels to contain the overflow of water. (Although officially, the Megatron is one huge chamber further up the network).

Seemingly forgotten for years, this complex system of underground waterways, gained worldwide attention when it was “rediscovered,” becoming a favourite for urban explorers, and even attracting guided tours.

The misconception is that these subterranean drainage channels were built in the mid-1800s, an effort to channel the huge flow of water from Sheffield’s three main rivers – the Don, Sheaf and Porter, but the real story is very different.

Let’s start with the Porter Brook, with its source on Burbage Moor, descending into Sheffield before disappearing into culverts in the city centre. During the late 19th century, sections of the Porter were covered over, partly because the water supply was so poor and had become a sewer, but also to allow for the construction of factories above.

The Porter Brook joins the River Sheaf, the river that gave Sheffield its name, in the Sheaf Valley at a location that becomes evident later.

The Sheaf Valley had historically been prone to severe flooding, the areas around Pond Street and Ponds Forge, particularly susceptible when the River Sheaf burst its banks, and rendering much of the land unusable.

The River Sheaf flows through Sheffield, joining the mighty River Don at Blonk Street Bridge, near to where old Castle Markets stood, and the site of long-lost Sheffield Castle.

Our story really begins with the arrival of the Midland Railway Company, connecting Sheffield with London, which had blundered on its original route, inconveniencing passengers to change at Rotherham Masborough Station and take a branch line to The Wicker.

By the late 1850s, the company made proposals to rectify the matter, bringing the direct line into Sheffield. The site chosen for the new railway station caused disbelief as it was in the valley through which the River Sheaf flowed.

In the 1860s, after gaining Parliamentary consent, land was cleared on a site that was bounded east by Granville Street, on the west by Pond Lane, at north by Harmer Lane, and south by Turner Street.

The platforms were to be built where the River Sheaf flowed, and so the whole distance of the river between Harmer Lane and Turner Street was spanned by three arches and then covered over. The Porter Brook was spanned with two arches, also enclosed, and a portion of the nearby Bamforth Dam (now Sheaf Square) was filled in.

“For months and months past, seeming chaos has reigned in Granville Street and the region adjoining. Thick-booted, muddy-smocked navvies have laboured along in dust and mud, fine weather and wet, pulling down houses and the foundations on which they stood, tearing up banks, blasting rocks, making huge caverns which they said were to serve for tunnels, heaping up and then carting away great mounds of earth. The lines of the rails will run over the bed of the River Sheaf, which is degraded to the condition of a sewer. The work is being undertaken by Messrs. Chadwick and Thurwall for £20,000.”

The Midland Station, now Sheffield Station, opened in 1870, its passengers forgetting that the River Sheaf flowed under their feet (now Platforms 5-8), before emerging again after Harmer Lane.

It was a huge success and by the late 1890s the Midland Railway Company was planning the expansion of the station, and the widening of the tracks.

In 1899, the land in front of the station was cleared and between 1900-1903 its facade was built further forward and surrounding land used for railway business.

The River Sheaf, between Suffolk Road and the Midland Station was arched over and covered, as was a section running underneath Sheaf Street towards Commercial Street. A little-known stream, Pond Brook, between Station Road and Harmer Lane was also diverted through another large culvert.

More importantly, the confluence of the Porter Brook and Sheaf was also covered and is now underneath the south end of Platform 5, close to where Platform 2A is. Thank you to Phil Jones, who volunteers for the Sheaf and Porter Rivers Trust, for explaining that today there is a large square wooden access cover, exactly over the confluence.

As to who funded what, is a matter of debate, but it is likely that the “sewer” system, as the River Sheaf was ingloriously relegated to, was funded and built by Sheffield Corporation.

And so, the first parts of the underground maze were completed, and hereon becomes something of mystery.

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Into the Megatron (2)

We’ve already looked at the building of Sheffield’s underground tunnel system around Sheffield Station and the ingenious method of “hiding” the Porter Brook and River Sheaf. (Available to read on a separate post).

In this post, we move on from Sheffield Station (formerly Midland Station), which had doubled in size in the first few years of the twentieth century, and resulted in long stretches of the River Sheaf bidding farewell to the light of day.

After the Midland Station, the River Sheaf emerged briefly at a weir, as it does now, close to what is now the Digital Campus.

It then flowed through further culverts under the Electric Light Works (now the front of Ponds Forge International Sports Centre). The river then streamed under Commercial Street and beneath what was once the site of Sheaf Market (now the Travelodge).

Onwards it flowed under Castlefolds Markets, until being freed at Exchange Street and flowing open-air until meeting the River Don at its confluence near Blonk Street. (Remember that the River Sheaf once ran alongside Sheffield Castle).

As elaborate as the underground tunnels were underneath Sheaf Valley , the most spectacular part of the network lay underneath Exchange Street, now known as the “Megatron Chamber” – “something excellent and impressive” – a massive arched brick-lined cathedral that dwarfed any man who stood inside.

The reason for the Megatron has been provided by Heather Smith and Phil Jones from the Sheaf and Porter Rivers Trust. It seems that the giant Megatron arch was built for a very specific purpose, to carry heavy old trams across the river on Exchange Street, which rises slowly up the hill, and get them into the city.”

From the Megatron, the River Sheaf flowed out into the open-air, past the old Alexandria Theatre. This last section was culverted over in 1916 after the demolition of the theatre, another massive scheme that allowed the eventual construction of Castle Market above, the rebuilding of Blonk Street and a tunnel entrance that allowed the Sheaf to flow straight into the Don.

The underground system of tunnels is Victorian engineering at its best.

The arched roofs were built with three layers of brick, strong enough to resist the huge torrents of water that the Porter Brook and River Sheaf threw at them during times of high flood.

Alas, as good as the system is, it has failed on occasions, with stories of the old Sheaf Markets flooding at high water, and then there was the memorable Sheffield flood of 2007 when Sheffield Station found its tracks underwater for several days.

A poignant reminder from the River Sheaf that it is still around.

Mostly, the tunnels are accessible to walk through, but should never be entered without permission and expert supervision.

Underneath Sheffield Station the sound of trains can be heard rumbling overhead, and in the lower reaches, bats skim the surface of the Sheaf with fish evident.

As part of the Returning Rivers to the City Scheme, Sheffield City Council is considering reopening the last few yards of the River Sheaf from the Megatron to the River Don, in a park to be called Sheaf Field.

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Sheaf Field Park

We’ve already had a look at the series of culverts and tunnels that hide the River Sheaf underneath Sheffield city centre.

The last part of the river to be covered was the stretch from the Megatron, underneath Exchange Street, towards the confluence of the River Don at Blonk Street Bridge.

This was covered in 1916 after the demolition of the Alexandria Theatre, another massive scheme that allowed the eventual construction of Castle Market above, the rebuilding of Blonk Street and a tunnel entrance that allowed the Sheaf to flow straight into the Don.

Following the demolition of Castle Market in 2015, Sheffield City Council announced that a park would be created between Castlegate and Exchange Street.

Alas, four years down the line, the plans are still on the table, but the council is committed to delivering the project.

Sheffield Council wants to take the roof off the underground culvert, which the river currently runs through and is in a poor state of repair, and bring the waterway back into the open, surrounded by grass, flowers, trees, seating and other landscaping. The aim is to make the area more attractive to visitors, bring in new investment and reduce the risk of flooding.

The scheme would also complement the proposed Castlegate development on the site of the former market, which the council and its partners are still pursuing, and which will feature the exposed ruins of Sheffield Castle.

The park has the working title of Sheaf Field.

A waterside meadow and an elevated viewpoint would be created at the waterside and low stone walls built overlooking the river. The weir within the Sheaf culvert will be lowered, and the river channel remodelled, to improve natural habitats.

The plans also involve using way markers or pavement art to follow the River Sheaf’s course where it remains in a tunnel under Castle Square, Sheaf Street, the railway station and through Granville Square. Also, temporary art installations and ‘interactive sound experiences’ could be set up in the Megatron.

In 2019, the Sheaf and Porter Rivers Trust was set up to promote and support the deculverting and improve the environment of the River Sheaf and Porter Brook. The group’s founders aim to open the waterways and are trying to recruit as many members as possible to help make that happen. One of their hopes is to make sure that Sheaf Field comes to fruition.