The Tyburn, the Fleet and the ground between them

Primrose Hill rises to 64 metres on a mass of London clay, and for most of its history the land around it was governed by water rather than by building. Two lost rivers frame the district. The Tyburn falls from the Hampstead hills, runs south along the western side of the hill and through Regent's Park, and reaches the Thames near Pimlico. To the east lies the valley of the Fleet, draining the same high ground towards King's Cross. Camden's own account of the borough's lost rivers adds a third, the Kilburn, and records that all of them were eventually absorbed into London's sewerage system, in large part because they had become badly polluted.

The Tyburn vanished in stages rather than at a stroke. By 1670 its lower reaches had already been diverted into the King's Scholars' Pond Sewer. Water drawn from it helped to create the boating lake in Regent's Park in the early 1800s. By the 1830s the river was culverted as far north as Primrose Hill itself, and in the 1860s it was formally converted into a waste sewer running between Hampstead and Westminster — the fate of nearly every stream in inner north London.

Barrow Hill: a Georgian reservoir on the doorstep

The largest piece of water engineering in the immediate neighbourhood is not a river but a reservoir. The West Middlesex Waterworks Company, founded in 1806 to supply Marylebone and Paddington, drew from the Thames at Hammersmith and from 1808 distributed through cast-iron mains. In 1825 it began a new reservoir at Barrow Hill, immediately west of Primrose Hill.

Built over 1825-28, it held 4,750,000 gallons, or roughly 21,600 cubic metres. The basin was almost rectangular, about 95 metres by 57 metres at the top, with sides sloping at around one in two to a maximum depth of 7.5 metres, lined throughout with brick laid to headers and served by cast-iron inlet, overflow and outlet pipes. A pumping station stood immediately to its east. It was open to the sky at first, and only roofed in about 1860 with brick barrel vaults carried on brick piers.

That roof was a legal requirement as much as an improvement. The Metropolis Water Act 1852 made it unlawful for any company to take water for domestic use from the tidal Thames after 31 August 1855, and required that from the end of that year all such water be effectually filtered and stored under cover. An alternative had already been examined: Thomas Telford's report of 1834 proposed abandoning Thames water altogether and bringing supply from the River Verulam at Watford to Barrow Hill through twin aqueducts sixteen miles long. It was never built.

From nine companies to one

The supply that reached these streets passed through several hands in the space of a century:

Records of the older site also show the ordinary uses a reservoir picks up over 150 years: pipes laid to tea pavilions, lavatories, wartime allotments and camp sites, and destruction caused by a V2 rocket in March 1945.

The canal, the interceptors and the draining of the hill

The one visible waterway is entirely artificial. The Regent's Canal Act received royal assent on 13 July 1812 and cutting began on 14 October that year, with James Morgan as chief engineer and the architect John Nash — a director of the company — folding the canal into his plan for the Prince Regent's north London. The Paddington to Camden Town section opened in 1816 and the full line to Limehouse on 1 August 1820, with thirteen locks including the Hampstead Road Locks at Camden. The canal's most violent moment came on 2 October 1874, when the barge Tilbury, carrying gunpowder, exploded beneath Macclesfield Bridge near the Zoo. Four people aboard were killed, the blast was reportedly heard twenty miles away, and the episode hastened the Explosives Act 1875. When the bridge was rebuilt its cast-iron columns were re-erected the other way round.

Foul drainage was reorganised in the same generation. After the cholera outbreak of 1853 and the Great Stink of 1858, Joseph Bazalgette, as chief engineer to the Metropolitan Board of Works, laid out more than 1,300 miles of brick sewers and four pumping stations, with five interceptor sewers north of the Thames. The relevant one here is the Northern High Level Sewer, which begins on Hampstead hill and runs east past Kentish Town and Stoke Newington and beneath Victoria Park to the head of the Northern Outfall Sewer at Wick Lane. The slopes north and east of Primrose Hill drain towards that line.

The hill itself needed work too. Eton College's portion was transferred to the government in 1841 and an Act of Parliament secured the land as public open space in 1842. The Crown then drained and levelled the ground after 1851 before adding the paths and planting that turned rough pasture into a park for the people. The smooth green slope that now sheds rainwater so neatly towards Regent's Park Road is a piece of Victorian civil engineering in its own right.