Ever since the "Thames Gateway" project was created in 1995, the river entry to London has changed considerably. This long-term scheme aimed to redevelop a combination of brownfield sites, farmland, and marshes lining the Thames Estuary into hundreds of thousands of new homes, new businesses and, in some cases, completely new towns. The area stretches from Docklands and Stratford in the west, to Southend-on-Sea and the Isle of Sheppey in the east.
As far as North West Kent is concerned, both the Bluewater Shopping Centre and Channel Tunnel Rail Link (CTRL - now "High Speed 1") have been catalysts for major development in the region. The commissioning of Ebbsfleet International station was the first stage of the "Ebbsfleet Garden City" project which, if current figures are to be believed, will create around 15,000 residential properties over a fifteen year period. This is further compounded by plans unveiled on 8th October 2012 for a theme park on the Swanscombe Peninsula, occupying land formerly used by one of the country's largest cement works. The pressures on existing infrastructure these schemes will bring, in light of the significant increase in the local population, has given rise to various transport proposals, one of which is the "Ebbsfleet Southern Link".
The "Ebbsfleet Southern Link" forms part of Network Rail's "Kent Route Study", published in 2017. This considers a series of infrastructure projects and rolling stock improvements which could boost long-term railway capacity in Kent and South East London. The scope of the study is from 2024 to 2044, which extends far enough into the future to account for when today's proposed developments - residential and commercial - have been completed and matured. The primary role of the "Ebbsfleet Southern Link" is to provide Ebbsfleet International station with a second direct line to London. Based on projected passenger growth figures, there will not be enough capacity on an improved high speed domestic service to St Pancras to completely absorb the increased demand for travel between the capital and Ebbsfleet. The passenger growth will not only stem from Ebbsfleet residents heading to London for work, but will also include visitors to the garden city, whether this be for the planned theme park on the Swanscombe Peninsula, or even for job opportunities. Additionally, South London has been identified as being the potential source of a large proportion of future travel demand to Ebbsfleet, but is an area which is bypassed by "High Speed 1" (HS1).
The key to forming a direct link between Ebbsfleet International and South London lies with the "Waterloo Connection", a disused 3½-mile stretch of double-track line. This connects the "Chatham" main line via Swanley to its south (Fawkham Junction) with HS1 to its north (Southfleet Junction) and, from September 2003 to November 2007, was used by "Eurostar" services running between Waterloo International, Paris, and Brussels. After this time, there was a brief episode of a weekly empty stock "Javelin" working over the line and a couple of rail tours in 2014 comprising these same electric multiple units. However, the connection was soon after decommissioned as a through line and, in 2016, it became a dumping ground for withdrawn Class 373 stock.
The line now known as the "Waterloo Connection" has the distinction of opening and closing twice. It was originally commissioned in 1886 as part of a double-track passenger branch line to the water's edge at Gravesend; ultimate closure of the last operational section between Fawkham Junction and Southfleet came in 1976. It was re-opened in 2003 as the "Waterloo Connection", subsequently closing to regular through traffic in 2007 on the commissioning of the CTRL's "Section 2". The line will open for a third time should the "Ebbsfleet Southern Link" go ahead.
Three ways of how to re-use the "Waterloo Connection" are being considered:
On the below diagram, your author has surmised the form Options 1 and 3 could possibly take, whilst not completely ignoring major structural obstacles which currently exist. If any viewers know otherwise on routing, your author would be happy to hear alternative suggestions - this is merely my personal speculation.
For Option 1, your author has input a flying junction between the "Waterloo Connection" and HS1, which is marked on the diagram by the fictitious name of "Southfleet Tunnel Junction". Conversely, a flat junction has been made to the south, marked by the name "Southfleet West Junction". A flat junction has been assumed here, given that this part of the line is not high speed and there will be no interaction with non-stop Eurostar services at this point.
Option 2 involves no physical connection with HS1 nor the North Kent Line, and the Kent Route Study mentions a car park location where the extended "Waterloo Connection" could terminate. Your author suspects the terminating platforms will be upon the area marked as "Car Park D" on the map in the Ebbsfleet International section.
Option 3 has been the most interesting to ponder. On the northern side of the A2 still exists ¾-mile of double-track capacity railway cutting of the 1886 line to Gravesend, which has escaped redevelopment. Perhaps the plan here is to re-use this cutting for a link to the North Kent Line, a London-facing connection with the latter being made east of Northfleet (marked on the diagram as "Blue Lake Junction").
Option 3 seems to hold the most operational flexibility, perhaps countered by requiring the greatest civil engineering works out of the three possibilities to commission. In theory, this scheme would allow trains from Swanley to directly access both the North Kent Line and Ebbsfleet International, the latter via Springhead Road Junction to reach the "high level" platforms.
There then exists the question of electrification: third rail or overhead wires? Depending on how far into the future this scheme is realised - whether nearer 2024 or 2044 - may determine which way this goes. Based on the height new footbridges are being built to on Kent lines, the long-term goal would appear to be that of electrification across the county to the 25 kV AC overhead system. Putting that aside, however, the retention of overhead wires for the "Waterloo Connection" seems natural for Option 1, given that HS1 is so equipped. As for Options 2 and 3, assuming county-wide overhead wire aspirations are still distant, then maybe the logic will be an extension of the third rail network. Regardless of whether or not the "Ebbsfleet Southern Link" becomes a reality, allowing 12-car trains to run between the "Chatham" main line and HS1, it certainly does make an interesting case study.