Issues facing the Mayor of Greater London, regarding underground tunnels and clay and chalk ‘water tables’ of London and the Home Counties
1) Water Supply
First any Mayor has to note that after an Ice Age which saw glaciers from the Arctic as far south as Luton to St Albans, the Thames / Isis River ran further North from its Oxfordshire / Cotswold start and the Thames, if it existed, had less tributaries, mainly within the current Thames basin of Greater London (Colne, Crane, Misbourne, Fleet, Walbrook, Brent, Pinn etc).
From the Tudors the industrialisation of London at sites such as near Kew and Chiswick for coal mining and brewing reduced the water table levels which made it easier for the tunnels of the Metropolitan Railway to be cut and cover built and later the tube tunnels to be excavated by tunnelling machines (The Greathead shield) and laid with cast Iron segments.
As such the current Thames Valley Park has a water supply that has been greater than its capacity, prior to the Twentieth century Resorvoirs it is why during the past 1000 years the Thames has been gradually tamed, first by Locks and then canals for bringing Water supply from the Cotswolds and Wales and for the carrying of Cargo / freight prior to the Railways and twentieth century main road network (The Grand Union Paddington /Slough Canals, Kennet and Avon and Lea Navigation). Without these (and the rerouting of theCOlne / Misbourne and Frasy Rivers in West Bucks and South West Herts, the underground part of terminal 5 would be even more prone to water flooding, and even now there is still the need to return sewage treatment capacity that was previously on the Terminal 5 site (the Perry Oaks sewage farm).
However as well as water extraction, where there is habitation there is also excretion. Since the nineteenth century there has been under both sides of the Thames sewers to Beckton and Thamesmead for Sewage, part transported by water from the smaller tributaries, flushing toilets and the used bathwater from baths with drains.
This is now at capacity and over the past two terms of office the incumbent Mayors have, in partnership with the Assembly and Greater London Water companies (such as Thames and Three Valleys) been examining the possibility of another ‘Deep Super Sewer’ from near Hammersmith by The A4 and behind Latimer School and the Hammersmith and Fulham town hall where it would extract some ‘clean river Thames water’ to push along its length the sewage it would take from London’s nineteenth century ‘sub surface Thames Relief’ sewers.
However its implementation could lose control of Hammersmith and Fulham Council by the current Mayor Johnsons Conservative Party in the 2014 ‘borough mid terms’ to his own four year term of office owing to the popularity of that park amongst other reasons. Yet not to do so risks a rising water table corroding Gas and Electricity and Rail / Road tunnels lower down the Thames or nearer the river itself with resultant pollution of the Thames that could cost him his mayoralty in 2016.
2) Railway tunnel maintenance
The tunnels under the Thames are at most 150 -160 years old and are made of Iron rings or brick cut and cover. However aside from maintenance of the under river Bakerloo and northern Line tunnels (done during the 1990s and 2000s as part of the Hungerford Bridge footbridge millennium improvements) and the new Waterloo and London Bridge station infrastructure for the Jubillee Line extensions, current issues are:
1) Can the proposed northern Line extension to Battersea Power Station site from Kennington be further extended to Clapham Junction main Line station
2) Could The Waterloo and City Line be further extended to Battersea Power Station and Clapham Junction so that it can have better Depot facilities under the Battersea Development, similar to the Central Line at White City. Since the Bankl platyforms would need to be extended, the spoil extraction point for the original building to the West of Mansion House station (Circle and District) might have to be used owing to the River Walbrook running to its East under the road Walbrook in the City by St Stephens Walbrook and Mansion House.
3) Can this be done without preventing further transfer of the Balham, Streatham and Mitcham Junction loops via Clapham Junction inner suburban to London Overground so as to increase capacity of Outer Suburban and South Coast services as part of Thameslink 2020, Crossrail 1, Crossrail 2 and the proposed Brighton Main Line 2 as part of ‘Gatwick 2’ on the South Downs if Boris Island is an idea that is too much at risk of flooding owing to rsing sea levels as part of climate change?