Aviation Strategy

Written Evidence from Testrad (AS 123)

 

1 Construction costs and investment

The cost estimates provided within the Testrad Limited LJIA Concept Report (Appendix 1) were indicative and based on the measurement of the key items with contingencies of 50% included. In addition a further 10% was allowed for project management, engineering, planning and the like. With a project of this scale and nature it is not considered appropriate at this preliminary concept stage to provide detailed breakdown of the sums. Inevitably there will be design developments and associated cost changes, both positive and negative, as the project moves through various stages of refinement.

The two indicative cost estimates included within the LJIA Concept Report are reproduced below. The difference between the two estimates is driven, primarily, through the cost of a bored tunnel from the Ebbsfleet Origin and Destination terminal to the airport platform as compared to the use of a surface rail system with only an immersed tube tunnel used for the final sub-sea part of the connecting route to the airport platform. The two indicative cost estimates in the version of the Concept Report in the Appendix have been reworked slightly to clarify this comparison.

It is clear that any airport development, or expansion of an existing facility, will require additional investment in surface access, which will require funding in the same way as any other road or rail investments. Public sector involvement in such investments will be essential.

As far as the airport itself is concerned, this will depend on the charges to be levied and how the basic land infrastructure is financed. We estimate that private investors would be able to get a return from much of the airport infrastructure, although some public risk capital might well be necessary at the outset

Item	Scope	Cost £m
Airport Platform	Site formation,	8,000
Airport Platform	Infrastructure (runways, concourse, cargo and services), transport connections and marine facilities	7,000
O/D Terminal	Main terminal building and transport connections	5,000
Transport Linkages	Main running tunnels. Service tunnels, emergency stations, rail and services infrastructure and trains	22,000
Existing infrastructure improvements	Upgrading of M25, Crossrail extension other minor rail works and local highway access	3,000
Logistics Centre	Creation of the logistic park infrastructure, services and utilities, administration facilities, tunnel connection for rail and road transport to the airport platform, including trains and road connections to M20	4,000
	Total	49,000

Item	Scope	Cost £m
Airport Platform	Site formation	8,000
Airport Platform	Infrastructure (runways, concourse, cargo and services), transport connections and marine facilities	6,500
O/D Terminal	Main terminal building and transport connections	4,500
Transport Linkages	Surface running tracks with tunnel connection to the Airport Platform. Rail and services infrastructure and trains.	9,500
Existing infrastructure improvements	Upgrading of M25, Crossrail extension other minor rail works and local highway access	3,000
Logistics Centre	Creation of the logistic park infrastructure, services and utilities, administration facilities, tunnel connection for rail and road transport to the airport platform, including trains and road connections to M20	4,000
	Total	35,500

As can be seen from the above tables there is no difference at the site formation level, however there is some saving for the airport platform in the second option due to the fact that the immersed tube will be coming in at a significantly shallower depth than the deeper bored tunnel in the first option. Similarly the depth of the bored tunnel at the O/D Terminal results in a saving at this location in second option. By far the most significant cost difference between the two options, £12,500m, comes through the replacement of the bored tunnels by surface running high speed rail tracks from the O/D Terminal at Ebbsfleet to the airport platform.

2. The Cost of Reclaiming Land

The Scheme as presented within the LJIA Concept Report is based on adopting a poldering approach to minimise the volume of sand required for reclamation purposes and as such minimising the potential environmental impact. To enable the poldering to take place it is necessary to introduce a cut-off wall along the perimeter of the airport platform with at least one cut-off wall across the width of the airport platform to allow accelerated construction. The cost of these works is very similar to the saving in the cost of the sand required if poldering was not adopted, however it clearly allows the site to be formed with a reduced level of disruption with associated faster construction programme. As given in the tables above the cost of forming the edge structures with the cut-off walls, cross bunds, filling to a level of +7 metres for all operationally critical areas (runways, aprons etc), and land drainage is estimated, with contingencies, to be some £8bn.

The total surface area of the airport platform amounts to some 115km2, giving a unit cost per m2 of approximately £70 to form the airport platform.

3. General Engineering Challenges

The challenges of constructing the airport platform are by no means unique and are similar to many port-related infrastructure developments. The emphasis has to be placed on creating an initial is land through normal dredging techniques which will then allow the creation of a supply base with supporting logistics, initially through marine craft and ultimately through a permanent shore link.

In the case of LJIA it is proposed that platform construction should commence at the western extremity with conventional reclamation techniques. In parallel marine accessed construction would be used to create a supply base for construction activities and which will ultimately be incorporated into the permanent works. The construction of the outer perimeter bund and its cut-off wall will be undertaken by marine-based floating craft. It is envisaged that rock from Scandinavia will be used for the protection of the outer bund in a similar manner to methods employed for many of the East Coast coastal protection schemes.

4. Specific Engineering Challenges

A specific challenge is how to make available areas of the final platform formation for the safe construction of airport infrastructure, including runways and ancillary works, without waiting for the whole proposed platform area of 115km2 to be complete. It is proposed that a cross-wall will be constructed across the full width of the platform releasing the western half of the completed reclamation area for infrastructure development. Reclamation of the eastern half of the platform will continue in parallel to the construction of infrastructure on the western half.

As noted above, it is proposed to introduce a poldering approach with the edge structure backed by a perimeter road and the runways at a reclaim level of +7m. We estimate that the edge structure will require a top level some 2m higher than runway and operational levels to further safeguard the airport from risk of overtopping allowing for climate change effects. Similarly we anticipate a significant piled cut-off wall to a depth of around -30m to ensure piping, erosion of soil through passage of water, does not undermine the edge structure. These design features have been included in our costs estimates.

In non-operationally critical areas the area of sea bed inside the bunded edge structure will be capped by a blanket layer and retained at approximately -2m. Equally it is envisaged that all buildings will be piled with their founding slab also set at -2m. As noted within the Concept Report the lower basement levels of the buildings will be used for non-critical operational activities.

A key aspect within the design development will be to ensure that the perimeter bund cannot be breached by a planned or accidental aeroplane impact, or indeed by a ship ramming the structure. The proposed perimeter arrangement with the edge structure backed by roads and runways to give a minimum depth of the order of 400m will ensure the integrity of the structure from such incidents. Equally the relatively shallow depths surrounding the airport platform, even allowing for tidal variations, will effectively limit the size of vessel reaching the structure.

5. Flooding, storm surge implications and costs

The outer Thames Estuary is subject to tidal flows driven by the interaction of tides from the North Sea and English Channel.  Flows in the northern part of the Thames Estuary are broadly aligned north east - south west whilst those in the south are orientated east-west.  Sand banks have, over time, formed and aligned themselves as a result of these tidal flows.  Swell waves generated by storms in the North Sea are generally dissipated by interaction with the banks such that waves in the outer Thames Estuary, inshore of the banks, are mostly associated with local wind conditions.  When high water levels are elevated by storm surge wave conditions can become more severe as depths of water over the banks allow propagation of waves over greater distances. 

On a mean spring tide high water levels of + 5.4m CD occur at the platform site. The Highest Astronomical tide at the site is +5.7m CD and extreme storm affected water levels for a 50 year return period is +6.9m CD.   Tidal flows are orientated east-west across the site and peak currents of about 2.5 knots occur during spring tides.  Under extreme conditions, when winds may affect the flows, peak currents of up to 3 knots may occur.  The prevailing and strongest winds at the site are from westerly and south westerly directions.  However, as the platform is sheltered from this direction, the largest waves approach from the north north east to north east sector with a significant height (Hs) of about 2.5m for the 50 year return period condition.  Wave conditions around the platform may be influenced by changes in exposure to different directions and the bund design will take this into account as well as any influence from long term trends and climate change on extreme water levels, winds and waves. 

The platform is not expected to significantly influence tide or surge propagation upstream into the Thames Estuary because at this location in the estuary the change in estuary cross section caused by the platform will be small.  A platform further upstream could have a greater impact.

In developing the concept consideration has already been given to the need for planning and design of the edge structure to resist storm surges and the sea level rises described, and indeed tectonic changes. The current cost estimate is based on providing a 1 in 1000 year level of protection. Further detailed joint probability analysis supported by in-situ wave and tide measurements will be undertaken as part of the design process. The cost of protecting against these events is already included within the estimate as they form an integral part of the structure itself. Equally further detailed design will build resilience into the structure to allow it to be extended to provide increased protection levels as and if considered necessary.

6. Implications of Coastal Erosion

Any potential development on the estuary bed will have some impact. The areas to pay attention to are the sand banks and navigation channels to the north of the platform which could be influenced by changes to flows and sediment transport that occur during the construction and operational phases. On the positive side the platform will influence wave conditions providing shelter in its lee on the inshore. 

The platform edge structure could also induce reflection from the platform potentially increasing wave conditions at some locations in proximity to the platform.  Changes to waves and currents and availability of mobile sediment may have an influence on sedimentation in navigation channels and the dynamic stability of the sandbanks in this area, as well as the potential to change the coastal morphology with a resulting impact on associated habitat, fishery and recreational use of these waters. 

However, the airport platform and its orientation (as well as suiting the runway configuration) has been planned and designed to minimise the impacts on tidal flows within the area. In essence it utilises the existing sandbank configuration and its existing deep-water channel alignments. Our preliminary numerical modelling has shown that there will be localised adjustments to the sea bed immediately outside the boundary of the airport platform as the tidal flows around the structure diverge. Equally some areas of siltation can be expected as the flows around the airport platform converge and flow velocities diminish. It should be noted that part of the land platform area already dries at low tide and thus the airport development becomes an extension of the drying area. The potential for erosion and longshore sediment transport in the coastal area may be mitigated by increased tidal velocities between the airport platform and the North Kent shoreline due to the constriction of the water area, and the reduction in the wave climate. Further investigation of this will be undertaken as part of the scheme development.

Temporary works during construction of the platform and transport links to the platform will be subject to sedimentation during the works and this will need to be managed.  Likewise dredging and placement of material into the platform will give rise to the release of some fine material into the outer Thames Estuary, and these fines may give rise to changes in suspended sediment concentrations and sedimentation.  Emphasis will be placed on a construction strategy for works activities to be carried out in such a way to minimise the release of fine material and thereby local impacts.

7. Impact on Shipping Channels

The airport platform has also been planned to have little or no impact on the existing shipping channels. The preliminary modelling undertaken predicts minimal wave or sediment implications both during and after construction. This will need more detailed analysis as the design is progressed. In addition the platform has been positioned to ensure that there are no airdraft restrictions imposed at the edge of any existing shipping channel. For these purposes an airdraft requirement of 80m has been taken which corresponds to the largest possible cruise ship. The largest container ships using ports have a lesser airdraft of 75m.

8. Platform to mainland linkages

The proposed airport platform will have a number of linkages with the shore. For passengers using the airport platform the main means of access will be either via trains running in the deep bored tunnel or through a shallow immersed tube tunnel for the surface running trains. It is also proposed that an immersed tube should be laid between the proposed logistics and cargo park on the Whitstable shoreline and the airport platform. This would be used for worker access to and from the airport, cargo transfer and maintenance operations. It is proposed that this will be a two-lane dual carriageway with a local train service running between the logistics park and the airport platform. In addition the former construction harbour will be used to allow marine access for waste transfer and the movement of loads which cannot be accommodated by the tunnel. Fuel supplies will be either piped in or barged in depending on the degree of flexibility required for supply. At the eastern side of the airport platform a cruise terminal will also be provided.

9. Settlement Requirements

The planning and design of the settlement criteria will be an important element in finalising the costs and programme for the works. Various techniques are available to accelerate the natural consolidation progress ranging from surcharging with wick drains to vibro-compaction techniques. The selected techniques will have to be considered in relation to the phased release of land for further development. The cost of ground improvements has been included in the cost estimates.