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Anatomy of a Junction: One

The King’s Scholars’ Pond Sewer: St. John’s Wood

When a fellow underground aficionado first ventured into a London sewer his planned journey began in St. John’s Wood, in an unremarkable section of the King’s Scholars’ Pond Sewer (K.S.P.S.). Unremarkable as it was the 5.5ft x 3.5ft egg shaped sewer bombarded John with curious new sights, sounds and smells. He later remarked “There is a fatal fascination about sewers, and whenever an entrance is opened, a crowd is sure to gather . .” (Hollingshead, John. Underground London. 1862). Pic. 1 – The junction as seen in 2010, looking downstream to the inspection gallery.

The same section of tunnel where John Hollingshead began his virgin sewer expedition in 1860 has seen considerable alteration over the past 150 years; in 2010 there’s certainly more to remark upon, and more so to bombard the senses. This short text goes some way to unravelling a complex and compact sewer junction. The K.S.P.S. runs for approx. five miles in a south-easterly direction from Hampstead to the Thames. Located within the most northerly portion of this five mile run, the section we’re looking at did not receive any attention during the groundbreaking overhaul of London’s Main Drainage, under Joseph Bazalgette, Chief Engineer of the Metropolitan Board of Works. For an eighty five year period, from it’s construction c.1825 (Fig.1) to the construction of the London County Council’s Middle Level Sewer No.2 (Fig.2) in 1910, it remained unaltered. The timing of Hollingshead’s visit did in fact mean he travelled the entire route of the K.S.P.S. prior to any of Bazalgette’s major alteration works. Fig. 1 – The original sewer tunnel pre alterations. Fig. 2 – 1910 interceptor works creating the first phase of the junction.

The connection to the MID LVL SWR No.2 was the first stage of works forming the basis of the junction as it appears today. This first junction was a relatively simple set up where dam boards were installed in the K.S.P.S. tunnel immediately downstream of a new connection which diverted the sewage flow into a circular brick pipe measuring 5.6ft in diameter. The diversion pipe dropped the flow down a series of steps (Tumbling bay) to the intercepting sewer passing beneath the K.S.P.S., as seen in Fig.2. Fig. 3 – 1940s Penstock works. Fig. 4 – 1980s works, being the last to date.

A further thirty years passed with no works in the immediate vicinity of the junction, then in 1940 a penstock chamber was built on the downstream side of the dam boards. This allowed the K.S.P.S. tunnel to be entirely sealed off no matter what the volume of flow, diverting all its content into the intercepting sewer. The new penstock could be operated from street level via a manual gear mechanism. Also at this time a new local sewer was connected to the K.S.P.S. at the same juncture, see Fig.3 above. Fig. 5 – Plan detail of the junction as it exists today, with markers for photo positions.

The final phase of works that created the junction as it exists today seems to have removed almost as much as it added, and oddly appears to have been something of a step backwards in some ways. c.1980 an inspection gallery, at about 10ft above the junction invert, was installed. The extension upwards, to the new gallery, of the original dam board chase(s) allowed boards to be manually inserted from above to completely seal off either the K.S.P.S. or the diverting pipe to the MID LVL SWR No.2 (see Fig.5 above). The 1940s penstock was then removed in favour of this seemingly more arduous option. Pic. 2 – Looking upstream. Note dam board chase in foreground.

With its various phases of work this junction chamber is certainly an interesting place to photograph and was an unexpected and pleasant surprise on our first journey through this section of tunnel. No doubt Mr. Hollingshead was with us in spirit. 😉 Category: Anatomy of a junction, King's Scholar's Pond Sewer · Tags: King's Scholars' Pond sewer, London, Middle Level Sewer No.2, River Tyburn, Sewer, St. John's Wood


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