Water supply to Primrose Hill

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1           Original Barrow Hill reservoir

In the late 18th century, when Camden Town started to develop, London was supplied by pumping from the Thames. The raw water intakes had to be sited progressively further upstream as water quality deteriorated due to pollution from growing industry and the expanding metropolis.

The Barrow Hill reservoir was constructed over 1825-28 by the West Middlesex Waterworks Company to hold 4,750,000 gallons (21,600 cu m) of water. Raw water was extracted from the Thames at Hammersmith, pumped to Barrow Hill and other reservoirs and from there distributed to customers in the area.

The original Barrow Hill reservoir was nearly rectangular in plan, measuring 95m by 57m at the top with sides sloping at about 1 in 2 to a maximum relative depth of 7.5m. The sloping sides and floor were lined with bricks laid uniformly to headers, with cast-iron inlet, overflow and outlet pipes on the sides. A bund of clay and earth retained all four sides.

Originally open to the sky, with a pumping station immediately to its east, the reservoir was roofed in about 1860 with brick barrel vaults carried on brick piers.

2            Telford Commission

By the early part of the 19C, the quality of London’s water supply was becoming notorious and the butt of satire from George Cruickshank and others. The ‘Telford’ Royal Commission was set up in 1828 to inquire into the quantity, quality and ‘salubrity’ of the water supply to the metropolis. It concluded that the complaints were well founded and that alternative sources of supply should be found

Thomas Telford, FRS, the distinguished Scottish civil engineer who is buried in Westminster Abbey, was commissioned to investigate schemes for improving supply for the Northern and Southern Districts. In his 1834 report (published shortly before his death) he proposed replacing the North Thames water companies’ source with a supply from the River Verulam at Watford. There was to be a source reservoir at Watford supplying the Barrow Hill reservoir via twin aqueducts 16 miles in length.

3            The scene in 1842

There are few paintings that feature the reservoir, but one that has recently come to light is by W. H. Penson, who was employed by the London & Birmingham Railway as a ticket collector. His painting is looking west towards Primrose Hill from the ticket office, which was located near what is now the end wall of Dumpton Place. This unusual and rather stylised view of Primrose Hill dates from around 1842.

What appears to be a kiosk on the summit of Barrow Hill is the pumping station of the reservoir constructed some fifteen years earlier. Chalk Farm Tavern is seen on the right with its fenced gardens, its attractions a destination for the Sunday stroll out of town through what had been a fine stretch of countryside. The London & Birmingham Railway, built five years before, features the Travelling Post Office heading towards Euston, and creates a jarring note as it intrudes on this scene.

The wall in the centre ground is the original boundary wall of Camden Station, set back from what is now Gloucester Avenue and separating the goods depot and railway from future residential land. The gate in the wall connected Camden Station with Chalk Farm Tavern. Staff from the depot would eat and drink at the Tavern, where pigeon was the staple lunchtime fare, pigeon shooting being a sport for which the Tavern was well-known.

The parallel lines in the foreground running towards the tracks are surface drains created by digging finger trenches for filling with gravel in the heavy clay and leading these trenches to a main drain.

4            Last days of old reservoir and historical reminders

The water supply pipework to Primrose Hill in 1956 is shown here. A number of disused pipes are shown and have been numbered.

Pipes No 1, on the side of Barrow Hill, describes  Supply to now demolished tea pavilion and Service to now demolished Lavs.

It is believed that a kiosk was transferred from the Great Exhibition to near Barrow Hill and upgraded in 1859 to tea rooms known as the Queen’s Pavilion. The tea pavilion was a tented structure, shown on Stanford’s map of 1862 as a Refreshment Lodge. It is shown in E. H. Dixon’s watercolour landscape of Primrose Hill, dating from around that time. The tea pavilion, no doubt substantially altered, and the nearby mens lavatories, were destroyed in March 1945 by the V2 rocket that landed next to the reservoir.

Pipes No. 2 (three sites) describe the supply to the wartime alotments. Pipes No. 3 (two sites) describe the supply to  wartime camp sites, including the main gun emplacement at the top of the hill and a site near the children’s playground which probably featured a water tank that could serve for fire-fighting.   

The pumping station was demolished around 1950. The roof was rebuilt in 1968, the piers being replaced by reinforced concrete columns supporting concrete beams and arches of pressed sheet aluminium.

The brick lining and roof columns showed signs of movement and, despite being repaired and reinforced, the reservoir was taken out of service in 2002 on safety grounds and stood empty awaiting the funds for rebuild. In the meantime, Thames Water relied on pumping water from other areas of London through the Thames Water Ring Main to supply the clean ­water needs of the area’s 280,000 residents, until the funds were available to replace the old reservoir.

5            New Barrow Hill reservoir

This was the first new reservoir to be built in London in over 100 years.

It was built on the site of the brick-built reservoir constructed in 1826. But, after the old reservoir was decommissioned in 2002, the land in front of the structure was sold and the Barrow Hill Estate constructed in what was valuable residential land in St John’s Wood, leaving very little space outside the reservoir’s footprint on which to build.

The reservoir consists of two separate cells formed with in situ concrete floors and walls and precast columns, beams and roof panels. The columns are on a 5m grid, and the walls are 6.5m high, although much of the construction is effectively below ground. A valve chamber sits between the two cells.

The new 28.4Ml capacity reservoir was constructed over 2013-2014 to be filled with potable water and in operation early in 2015.

As one of 26 similarly sized storage tanks around London, the Barrow Hill reservoir plays an important role in ensuring the resilience of supply, its capacity providing the ability to move water around the ring main with greater efficiency.

The new reservoir is topped by a grassed roof that uses a seed with shallow roots for the roof itself.  The green roof comprises a free-draining, nutrient-poor sand/gravel dominated growing medium with a range of particle sizes. It has been recommended by London Borough of Camden ecologist that the roof is seeded with an acid grassland and wild flower mix, using species typically found on lowland acid grassland habitats in London. Experience in the wider area has shown that self colonisation can lead to a lack of floral diversity at roof level and the encroachment of invasive species.

The sloping sides of the mound that covers the concrete structure are believed to be seeded with a neutral grassland seed mix, a grass mix found in the adjacent park, underlain by a drainage layer. The lower parts of this slope were undisturbed by construction, so remain essentially unchanged. Where there was disturbance, it is assumed that a similar free-draining, nutrient-poor sand/gravel dominated growing medium with a range of particle sizes has been adopted for the side slopes.

It should be noted that Thames Water’s landscape proposals were set out in their Landscape and Ecology Management Plan, prepared as part of the planning application (see plan). Their proposals show many scattered trees on the slopes of the reservoir, which it seems were never planted.

6            Monitoring of seepage from the reservoir

Barrow Hill Reservoir is a Statutory Reservoir under the Reservoirs Act. It is important that the grass is regularly cut to facilitate monitoring of the condition of the reservoir given the very close proximity of the surrounding population. Thames Water will have a manual for reservoir maintenance which includes keeping all embankment slopes mown.

As a rule, the slopes of embankment dams should be kept clear of trees and other vegetation that might have penetrating roots or cause uneven run-off rivulets leading to erosion channels. However, Barrow Hill is a reinforced concrete (RC) water retaining structure and it may be assumed that the earth embankments are purely cosmetic rather than having a structural function.

Monitoring of seepage varies from site to site. Ideally the slope of embankment dams should be visible to allow tracing of any cracks that might form and monitoring of damp patches indicative of seepage. Barrow Hill reservoir, however, is of RC construction and the principal means of monitoring reservoir performance is via the embankments toe drains that discharge to a well on the SW corner where seepage can be measured.

Thames Water uses an automated mechanical mower as the embankment slopes are steep. This has caused some damage to the earth cover to the reservoir.

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