Case studies

Panshanger (DeHavilland Park), Welwyn Garden City

CampbellReith developed a drainage design that was sympathetic to the site’s constraints and was an integral part to the proposed landscaping.

Client: Homes England

Project value: £13.8m (Infrastructure)

Project start and finish dates: 2020 - Present

Masterplanning Lead: fabrik

Planning Lead: Luken Beck

Utilities: FLOH

Cost/Contract Management Lead: Allen Dadswell Construction Consultants

CampbellReith with EHDC-RegenCo has been appointed as multi-disciplinary Consultant taking forward the Reserved Matters Application for the spine road and supporting infrastructure to unlock the development of 650 new homes and submitting an Outline Application for Phase 2 to extend the development by 215 additional units.

To enable the submission of the RMA for an efficient and appropriately located Spine Road we revised the existing masterplan to deliver enhanced placemaking (including a re-located local centre) and land value resulting in a successful section 73 (S73) application. The team is actively working with Homes England to develop the phasing and disposal strategy by identifying a haul road to facilitate construction access and minimise impact on the main spine.

CampbellReith has undertaken a site wide cut and fill model to inform and support the drainage strategy, which has provided added value in identifying how the land parcels would link to the spine road and secondary/tertiary road network. That information would allow Homes England to derisk the site and provide enhanced information to potential future developers.

We undertook extensive consultation with statutory stakeholders (to address and resolve highways, transport, drainage, heritage, ecology and archaeology issues) and local community representatives (including ward councillors) and residents. This included extensive social media coverage as well as a Covid-compliant public exhibition at the height of the pandemic. We managed to help address residents’ concerns such that residents’ objections were removed from the S73 application and ward councillor issues adequately addressed, and their ‘call-in’ of the S73 application was removed enabling an expedited delegated approval.

As part of the Phase 2 application, CampbellReith’s Transportation team reviewed and updated the previous analysis undertaken on the local network to clearly demonstrate the likely impact in traffic terms. A Transport Assessment was submitted in support of the application, which included appropriate mitigation measures in the form of junction upgrades, along with a dedicated Residential Travel Plan to introduce measures which would reduce the reliance on the private car and encourage sustainable forms of travel.

Engaging closely with the Lead Local Flood Authority throughout the P1 RMA and P2 OPA, CampbellReith developed a drainage design that was sympathetic to the site’s constraints and formed an integral part to the proposed landscaping.

Multi-disciplinary coordination between our highways and drainage engineers allowed us to develop a site wide levels strategy that minimised the impact earthworks and maximised the use of gravity sewers across an extremely flat site. Early input into the highway layout resulted in the incorporation of a SuDS corridor for the capture and treatment of highway runoff. This along with the use of conveyance swales and multi-use basins throughout the landscaping areas of the site, resulted in a scheme where SuDS not only offered water quality, biodiversity and flood risk benefits, but played an important role in contributing to the overall characteristics of the development. 

The planning application was accompanied by an Environmental Statement, which was submitted voluntarily by Homes England. The scope of the Environmental Statement was informed by a preceding Environmental Impact Assessment (EIA) that was submitted for the approved Phase 1 development and key topic areas included traffic and transportation, landscape and visual, cultural heritage and the water environment.

The only significant residual effects predicted following the EIA process were for the changes in the landscape features of the site itself and a limited number of viewpoints at Year 1. As landscape planting matures the predicted visual effects of the Proposed Development reduced to non-significant.

Our Geotechnical and Land Quality Teams undertook desk-based reporting, followed by the design, procurement and management of ground investigation works to inform the detailed design of the spine road, and also providing preliminary design information to inform the future development of adjacent, predominately residential, land parcels. 

The investigations were tailored to investigate identified geohazards and contamination sources, including the significant subsidence risk from chalk dissolution, landfill and aviation fuel tanks, whilst also considering planning conditions associated with the re-use of sand and gravel minerals and decommissioning of exploratory holes to avoid contamination of underlying aquifers.

The works culminated in a Phase II Geo-environmental Report and Mineral Assessment and Strategy for the entire DeHavilland Park development area, with the latter informing the sustainable re-use of site won soils during future development. The Interpretative Geotechnical Report for the spine road concluded ground improvement through rapid dynamic compaction paired with grouting of identified features was required to mitigate the risk of subsidence from chalk dissolution. Additional phase specific ground summary reports were produced to support the technical information packages and their disposal to plot developers.

Key Contacts

Partners

Bava Sathan

Services

Civil

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Environmental

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Geotechnical

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Highways & Transport

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