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6.0 Infrastructure
06 Infrastructure
6.1 Infrastructure First
6.1.1 At this stage, the site and its intricacies are well understood – as is the planning, geographical and local context. The site has been rigorously mapped giving a precise account of the land that is, and is not, available for development - as well as the ways in which various site features should be treated.
6.1.2 The final building block needed to create a cogent and comprehensive Masterplan which unifies all these features is, therefore, Infrastructure and EBC’s commitment to Infrastructure First. As Local Authority, EBC recognises that all too often, Infrastructure is an afterthought within developments – planned, designed and delivered last. One Horton Heath poses an unrivalled opportunity to do things in a different order – the correct order.
6.1.3 Infrastructure First encapsulates the commitment to ensuring infrastructure is properly planned, appropriate to the needs of the development and local area, and is delivered as early as possible and, on that basis, is a matter which must be taken into account as part of the process of establishing a Masterplan.
6.1.4 Whilst Infrastructure is a very broad term which we use here to encompass just about any component of the development which is not ‘a building.’ The terms refers to all of the aspects which are ancillary to development of this scale. For ease, we break down ‘Infrastructure’ into broad categories:
Grey Infrastructure
6.1.5 The man-made engineering features which are essential to unlock and support a new major development, such as:
• Roads and footpaths
• Bus routes, bus stops, and other sustainable transport features
Blue Infrastructure
6.1.6 Infrastructure associated with surface water – drainage features, above and below ground:
• Drainage
• SUDs features
• Watercourses
Green Infrastructure
6.1.7 Natural infrastructure installed to support the development:
• Landscape planting
• Biodiversity enhancements
• Tree corridors and hedgerows
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INFRASTRUCTURE FIRST
6.1.8 When planned naturally, as is the case here, Infrastructure often bears a ‘chicken-and-egg’ relationship to the Masterplan. Infrastructure is needed to support the Masterplan, which needs to accommodate the Infrastructure, which must be sized appropriately to fit the Masterplan – and so on and on.
6.1.9 This section does not seek to capture the full journey which has resulted in the extensive and carefully-planned infrastructure that forms a critical part of this development proposal. Rather, this section should be read alongside the One Horton Heath Infrastructure Development Plan (IDP), a significant document in its own right which captures the background, context, decision-making process and proposals for all of the key infrastructure, as well as proposing means for delivering that infrastructure as early as possible.
6.1.10 What this section does is consider the infrastructure which is a necessary precursor to any consideration of the Masterplan. Already, preceding sections have made reference to certain aspects of infrastructure such as the Link Road. There are some infrastructure requirements that are so significant that they are material considerations in preparing a Masterplan and require land or other assets to be made available in their own right.
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6.2 A New North-South Route
6.2.1 A need has long been identified for better movement infrastructure into Eastleigh Town Centre from the South and East – not just for cars and motor vehicles, but for pedestrians and cyclists. In practice, this means either (a) significant improvements to the existing road corridor through Horton Heath, Fair Oak and Bishopstoke; (b) a new road (along with pedestrian/ cycle infrastructure) altogether which bypasses these existing corridors, or (c) a combination of both.
6.2.2 One Horton Heath rests squarely in the centre of this movement corridor, and fills-in much of the desire-line. It is therefore a longstanding expectation that this site will provide a new road which bypasses the existing roads and junctions through Horton Heath; the new road should be as direct and as efficient as constraints and land ownership allow.
6.3 HGV Routing
6.3.1 In addition to the requirement for a new NorthSouth route, there is a longstanding local issue associated with Chalcroft Distribution Park. Formerly a naval railway station, this site is now a small private industrial park which is home to multiple businesses. The distribution park generates extensive HGV traffic which, at present, uses existing roads which are not really fit for purposes. The North-South route provides an excellent opportunity to remove this issue altogether – by providing a route directly from Burnetts Lane, at the access to Chalcroft Distribution Park, straight onto Bubb Lane which is large distributor road leading directly into Hedge End and the M27.
6.3.2 The previous two planning consents for the site included detailed planning consent for three roundabouts, at Bubb Lane and Burnetts Lane (along with a small section of road connecting the two) and Allington Lane – collectively, the accesses into the site.
6.3.3 These roundabouts also mark the Northern and Southern extents of the North-South route through the site, as well as the whole of the section of road which would take traffic from Chalcroft Distribution Park.
6.3.4 Given the longstanding aspiration for the infrastructure which these elements represent; the immediate benefit that could be realised through delivery of the Bubb Lane/ Burnetts Lane link road in isolation; being satisfied with their capacity and having detailed planning permission, it was decided early in the process to treat these elements as fixed and to deliver them as permitted. Construction of those elements started in April 2020 and is due to complete in early 2021.
6.4 Surface Water
6.4.1 Design of site drainage needs to respond, in part, to the Masterplan – to be informed by the location, scale and nature of development. However, it also needs to respond to the existing landscape and natural capital of the site. There are some key principles which must be considered first so that adequate provision can be made within the Masterplan to properly accommodate blue infrastructure.
6.4.2 Surface water drainage has a vital part to play in achieving the Project Brief as well as the more basic function of ensuring the site drains safely and appropriately without increasing flood risk. Drainage can also contribute to improved water quality, as well as providing opportunity for biodiversity enhancement.
6.4.3 Surface water drainage will follow a clear hierarchy which will ensure that all run-off passes through three forms of filtration; the use of naturalised filtration techniques will be preferred. This hierarchy is well demonstrated by the proposed SUDs management train diagram, which is described diagrammatically on the following pages.
6.4.4 Naturalised SUDs features will be carefully designed so as to be appropriately located – designed according to topography and to complement the site’s existing wildlife networks. Wherever possible, naturalised SUDs features such as basins and swales will be designed to contribute to good water quality and to biodiversity.
6.4.5 These important features will consist of a series of both wet and dry arrangements which, accompanied with appropriate planting, attract a variety of species. Seminatural drainage features, such as rain gardens, can also be used in more urban areas to contribute to achieving good quality and improving landscape networks.
6.5 Foul Drainage
6.5.1 Foul drainage is another critical consideration with a site of this scale. By virtue of the topography alone, it is evidently not possible to drain the entire site to a single location (i.e. a sewer connection) via gravity – some form of pump and rising main will be required. Further analysis of site levels demonstrates that, as a minimum, two pumps will be necessary.
6.5.2 Although at this stage in the project it is not necessary to design foul drainage in detail, accommodating these two pumps is critical. Foul drainage pumps built in accordance with “Sewers for Adoption” – along with any storage which may be required – are land-hungry features. Additionally, these installations have significant environmental health considerations to take into account including odour, noise and visual impact.
6.5.3 Therefore, it is vital that the Masterplan accommodates such infrastructure, from the outset, in a location that not only works in terms of topography but can also be separated from residences and amenity so as to avoid detrimental impact.
B. PARKING AREA RUN-OFF
Residential parking areas have a low pollution hazard level, and therefore benefit from modest ‘at-source’ treatment
Permeable paving will create a layer of vertical filtration, comprising a subsurface gravel matrix to filter, adsorb, biodegrade and capture sediment
C. PUBLIC ROAD RUN-OFF
Public roads areas have a medium pollution hazard level, and therefore greatly benefit from ‘at-source’ treatment
Roadside swales will create a layer of vertical and horizontal filtration as part of a site-wide conveyancing strategy
Sediment forebays provide retention for a portion of the first-flush stormwater run-off whilst dissipating the energy of incoming surges, and help to isolate sediment deposition
Micro-pools enhance attenuation capacity and improve filtration by helping to increase the pollutant removal pathway. They also enable a more practical maintenance strategy, and encourage greater biodiversity by offering more varied potential habitats
Aquatic benches are created along the edges and throughout the basins, to offer further opportunity and variety in biofiltration. Nitrogen-reducing native marginal and aquatic species will be included, as well as creating shallow wet/marshy grassland areas
Mechanical flow control measures will ensure that, once surface water has been treated and attenuated through the SUDS management train, it can be carefully released into the existing watercourses at a rate that matches the existing run-off profile. It will also be possible to control the flow of storm surges and actively prevent the current risk of downstream flooding
